Chapter 4 A Tour of the Cell.

Chapter 4 A Tour of the Cell

Biology and Society: Antibiotics: Drugs that Target Bacterial Cells
Antibiotics – drugs that disable or kill infectious bacteria – are a marvel of modern medicine. Most antibiotics are naturally occurring chemicals derived from microorganisms. After the isolation of penicillin from mold in 1928, a revolution in human health followed. Fatality rates from infectious diseases plummeted. © 2013 Pearson Education, Inc. 2

The goal of antibiotic treatment is to harm the invading bacterium leaving the human host safe. Most antibiotics target only the bacterium, not the human host cell. Erythromycin and streptomycin bind to the bacterial ribosome, an enzyme it uses to produce proteins. Ciprofloxacin, the antibiotic of choice to treat anflax, targets a specific enzyme in that bacterium. © 2013 Pearson Education, Inc.

Penincillin, ampicillin and bacitracin disrupt the synthesis of bacterial cell walls. This is a major part of this chapter – to learn about cells and their function. Many organisms, like bacteria, are single-celled. More complex organisms, like plants and humans, are multicelled. In this chapter we will explore the structure and function of cells. © 2013 Pearson Education, Inc.

Figure 4.0a Figure 4.0 Two kinds of cells: Bordetela pertussis and human throat cells (part 1)

Figure 4.0b Figure 4.0 Two kinds of cells: Bordetela pertussis and human throat cells (part 2)

Figure 4.0 Figure 4.0 Two kinds of cells: Bordetela pertussis and human throat cells

The Microscopic World of Cells
Organisms are either single-celled (e.g. bacteria) or multicelled (e.g. plant and animal). Three examples of human cells are muscle cells, nerve cells and red blood cells. Everything your body does is controlled by trillions of cells. © 2013 Pearson Education, Inc.

Most antibiotics kill bacteria while minimally harming the human host by binding to structures found only on bacterial cells. Some antibiotics bind to the bacterial ribosome, leaving human ribosomes unaffected. Other antibiotics target enzymes found only in the bacterial cells. © 2013 Pearson Education, Inc. 9

THE MICROSCOPIC WORLD OF CELLS
Organisms are either single-celled, such as most prokaryotes and protists, or multicelled, such as plants, animals, and most fungi. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 10

Microscopes as Windows on the World of Cells
Before the 1600’s, there were no microscopes to study the structure and function of cells. Light microscopes can be used to explore the structures and functions of cells. When scientists examine a specimen on a microscope slide, light passes through the specimen and lenses enlarge, or magnify, the image. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 11

Two important factors in microscopy are magnification and resolving power. Magnification is an increase in the object’s image size compared to its actual size. Resolving power is the ability of an optical instrument to show two objects as separate. The resolving power for your eye is 0.1 mm. The resolving power for a light microscope is 0.2um. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at

Cells were first described in 1665 by Robert Hooke who examined a slice of oak tree bark. By the mid-1800s, the accumulation of scientific evidence led to the cell theory, which states that all living things are composed of cells and all cells come from other cells. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at

Science advanced greatly in the 1950’s with the use of powerful new electron microscope. The electron microscope (EM) uses a beam of electrons, which results in 100-fold better resolution than light microscope. Two kinds of electron microscopes reveal different parts of cells. Scanning electron microscopes (SEMs) examine cell surfaces. Transmission electron microscopes (TEMs) are useful for studying the internal structure of a cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at

The most powerful modern electron microscopes can distinguish objects as small as 0.2 nm. The highest power electron microscope have magnifications of about 100,000X. However, preparing a cell for electron microscope means it has to be fixed and killed so this type of microscope does not allow us to visualize a cell in activity. © 2013 Pearson Education, Inc.

(for viewing living cells)
Figure 4.1a Light Micrograph (LM) (for viewing living cells) Light micrograph of a protist, Paramecium Figure 4.1 The protist Paramecium viewed with three different types of microscopes (part 1)

Scanning Electron Micrograph (SEM) (for viewing surface features)
Figure 4.1b Scanning Electron Micrograph (SEM) (for viewing surface features) Scanning electron micrograph of Paramecium Figure 4.1 The protist Paramecium viewed with three different types of microscopes (part 2)

Transmission Electron Micrograph (TEM)
Figure 4.1c Transmission Electron Micrograph (TEM) (for viewing internal structures) Transmission electron micrograph of Paramecium Figure 4.1 The protist Paramecium viewed with three different types of microscopes (part 3)

Figure 4.2 Figure 4.2 An electron microscope

Figure 4.3 10 m Human height 1 m Length of some nerve and muscle cells 10 cm Unaided eye Chicken egg 1 cm Frog eggs 1 mm 100 µm Plant and animal cells Light microscope 10 µm Nuclei Most bacteria Mitochondria 1 µm Smallest bacteria Electron microscope 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms Figure 4.3 The size range of cells

The Two Major Categories of Cells
The countless cells on Earth fall into two basic categories: Prokaryotic cells — Bacteria and Archaea and Eukaryotic cells — cells of the Domain Eukarya: protists, plants, fungi, and animals. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 21

All cells have several basic features. They are all bounded by a thin plasma membrane, which regulates the traffic of molecules between the inside of the cell and the surroundings Material must move across the plasma membrane. Inside all cells is a thick, jelly-like fluid called the cytosol, in which cellular components are suspended. All cells have one or more chromosomes carrying genes made of DNA. All cells have ribosomes, tiny structures that build proteins according to the instructions of genes located in the DNA. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 22

Although similar in many ways, prokaryotic cells and eukaryotic cells have several differences Prokaryotic cells are older than eukaryotic cells. Prokaryotes appeared about 3.5 billion years ago. Eukaryotes appeared about 2.1 billion years ago. Prokaryotic cells are usually smaller than eukaryotic cells and simpler in structure. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 23

Eukaryotes Only eukaryotic cells have organelles, membrane-enclosed structures that perform specific functions. The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA and is surrounded by a double membrane. Prokaryotes Do not have a nucleus or organelles. The DNA is spread out in the cytoplasm of the cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 24

A prokaryotic cell lacks a nucleus. Its DNA is coiled into a nucleus-like region called the nucleoid, which is not partitioned from the rest of the cell by membranes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 25

A eukaryotic cell is like an office building that is separated into cubicles for different functions. The organelles are the cubicles with specific roles to play. The membranes of the organelles maintain a unique chemical environment for certain tasks to be performed. © 2013 Pearson Education, Inc.

Surrounding the plasma membrane of most prokaryotic cells is a rigid cell wall which helps to protect the cell and maintain its shape. In some bacteria, a sticky outer surface called a capsule surrounds the cell wall. Capsules provide protection and help bacteria stick to certain surfaces. Some capsules prevent white blood cells in animals from engulfing the bacteria Some bacteria also have pili and flagella © 2013 Pearson Education, Inc.

Cell wall (provides rigidity)
Figure 4.4a Plasma membrane (encloses cytoplasm) Cell wall (provides rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) Figure 4.4 An idealized prokaryotic cell (detail)

Figure 4.4b Colorized TEM Figure 4.4 An idealized prokaryotic cell (TEM)

An Overview of Eukaryotic Cells
Eukaryotic cells – animals, plants, protist and fungi - are fundamentally similar. The entire region between the nucleus and plasma membrane is the cytoplasm. (This term is also used to refer to the liquid in a prokaryotic cell.) The cytoplasm consists of various organelles suspended in the liquid cytosol. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 30

Most organelles are found in BOTH plant and animal cells. However, only plants are organelles called chloroplasts which are the sites of photosynthesis Also, only animal cells have organelles called lysosomes which serve as garbage dumps and recyclers in the cell © 2013 Pearson Education, Inc.

Unlike animal cells, plant cells have chloroplasts, which convert light energy to the chemical energy of food in the process of photosynthesis, and protective cell walls. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 32

Only animal cells have lysosomes, bubbles of digestive enzymes surrounded by membranes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students typically cannot distinguish between resolution and magnification. However, pixels and resolution of digital images can help “clarify” the distinction. Consider printing the same image at high and low resolution or enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students frequently equate the functions of mitochondria and chloroplasts as alternative ways to acquire usable energy. This often leads to the conclusion that animal cells have mitochondria but not chloroplasts and that plant cells have chloroplasts but not mitochondria. Plant cells have both. Teaching Tips 1. Here is a chance to challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, and so on. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a way to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, and so on. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes. (They need not state their answers publicly, to avoid embarrassment.) 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope and a “compound” light microscope using microscope slides. The way these scopes function parallels the workings of EMs. Dissection microscopes are like an SEM—both rely on a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye—the way a compound light microscope or TEM works! 4. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 5. This is a place where a visual image comparing a prokaryotic and eukaryotic cell can be very helpful. These cells are strikingly different in size and composition. A visual reference point instead of just abstract ideas and traits will be a continual reminder for your students during your discussion of these cells. 6. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter by a factor of ten translates into a much greater difference in volume. Students might be challenged to recall enough geometry to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 7. Germs—here is a term that we learn early in our lives but that is rarely well defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (a) bacteria (prokaryotes), (b) viruses (not yet addressed), and (c) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 8. Some instructors have reported great success by challenging their students to make analogies to the functions of the many organelles discussed. Students may wish to construct one inclusive analogy between a society or factory (used in the text) and a cell or to construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and differences/exceptions. 9. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at 33

IDEALIZED ANIMAL CELL Ribosomes Centriole Cytoskeleton Lysosome Plasma
Figure 4.5a IDEALIZED ANIMAL CELL Ribosomes Centriole Cytoskeleton Lysosome Plasma membrane Nucleus Mitochondrion Rough ER Smooth ER Golgi apparatus Figure 4.5 A view of an idealized animal cell and plant cell (part 1)

Cytoskeleton Central vacuole Mitochondrion Cell wall Nucleus
Figure 4.5b Cytoskeleton Central vacuole Mitochondrion Cell wall Nucleus Chloroplast Rough ER Ribosomes Plasma membrane Channels between cells Smooth ER Golgi apparatus IDEALIZED PLANT CELL Figure 4.5 A view of an idealized animal cell and plant cell (part 2)

MEMBRANE STRUCTURE The plasma membrane separates the living cell from its nonliving surroundings. It is very thin – it would take 8,000 cell membranes to equal the thickness of a piece of paper. The plasma membrane helps to regulate what enters and leaves to cell at any given time. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 36

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins
The remarkably thin membranes of cells are composed mostly of lipids and proteins. The lipids belong to a special category called phospholipids. These molecules have two fatty acid side chains and one phosphate group making it partially hydrophobic and partially hydrophilic Phospholipids form a two-layered membrane, the phospholipid bilayer. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 37

The fatty acids intermingle with each other providing the inner part of the membrane. The hydrophilic phosphate head groups are in touch with the water on the inside and outside of the cell. The hydrophobic fatty acid tails intermingle with each other. Most membranes have specific proteins embedded in the phospholipid bilayer. These proteins help regulate traffic across the membrane and perform other functions. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.)

The plasma membrane is a fluid mosaic. Fluid because molecules can move freely past one another. A mosaic because of the diversity of proteins that float like icebergs in the membrane. Some bacteria can cause illness by penetrating the plasma membrane of the cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.)

Cytoplasm (inside of cell)
Figure 4.6a Outside of cell Hydrophilic head Hydrophobic tail Phospholipid Cytoplasm (inside of cell) (a) Phospholipid bilayer of membrane Figure 4.6 The plasma membrane structure (part 1)

(b) Fluid mosaic model of membrane
Figure 4.6b Outside of cell Proteins Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Cytoplasm (inside of cell) (b) Fluid mosaic model of membrane Figure 4.6 The plasma membrane structure (part 2)

The Process of Science: What Makes a Superbug?
Some bacterial cause disease by rupturing the plasma membranes of human immune system cells. Particularly dangerous strains of bacteria, known as Methicilin Resistant Staphylococcus Aureus (MRSA), are unaffected by several common antibiotics. These bacteria are commonly found on the skin and cause a “staph” infection Staph infections can cause serious, even life-threatening conditions. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 42

Most staph infections can be treated with antibiotics, but MRSA is resistant to the antibiotic methicillin. These infections have become more common and even show up in gyms and schools. In 2007, scientists at the National Institutes of Health (NIH) studied one deadly strain of MRSA. © 2013 Pearson Education, Inc.

Observation: Some bacteria use a protein called PSM to disable human immune cells by forming holes that rip apart the plasma membrane. Question: Does PSM play a role in MRSA infections? Hypothesis: MRSA bacteria lacking the ability to produce PSM would be less deadly than normal MRSA strains. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 44

Methicillin-resistant Staphylococcus aureus (MRSA)
Figure 4.7b Colorized SEM Methicillin-resistant Staphylococcus aureus (MRSA) Figure 4.7 How MRSA may destroy human immune cells (SEM)

Figure 4.7a-1 Colorized SEM 1 MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) Figure 4.7 How MRSA may destroy human immune cells (step 1)

Figure 4.7a-2 Colorized SEM 1 MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) 2 PSM proteins forming hole in human immune cell plasma membrane PSM protein Plasma membrane Pore Figure 4.7 How MRSA may destroy human immune cells (step 2)

Figure 4.7a-3 Colorized SEM 1 MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) 2 PSM proteins forming hole in human immune cell plasma membrane PSM protein Plasma membrane Pore 3 Cell bursting, losing its contents through the holes Figure 4.7 How MRSA may destroy human immune cells (step 3)

Experiment: Researchers infected seven mice with normal MRSA and eight mice with MRSA that does not produce PSM. Results: All seven mice infected with normal MRSA died. Five of the eight mice infected with MRSA that does not produce PSM survived. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 49

Conclusions: MRSA strains appear to use the membrane-destroying PSM protein, but factors other than PSM protein contributed to the death of mice (possibly other membrane-destroying proteins). © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 51

Cell Surfaces Plant cells have rigid cell walls surrounding the membrane. Plant cell walls are made of cellulose, protect the cells, maintain cell shape, and keep cells from absorbing too much water. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 52

Cell Surfaces Animal cells lack cell walls and
Have cell junctions – structures that connect cells together into tissues, allowing them to function in a coordinated way. typically have an extracellular matrix, which helps hold cells together in tissues and protects and supports them. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. For example, membranes and our skin (a) detect stimuli, (b) engage in gas exchange, and (c) serve as sites of excretion and absorption. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. That all of this organization naturally emerges from the properties of phospholipids is worth sharing with your students. 2. You might wish to share a very simple analogy that seems to work with some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy to find exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) 53

THE NUCLEUS AND RIBOSOMES: GENETIC CONTROL OF THE CELL
The nucleus is the chief executive of the cell. The top managers of the cell are the genes that are the instructions for the cell to make specific proteins (Example: the hemoglobin gene is a stretch of the DNA on one chromosome that tells the cell how to synthesize a hemoglobin protein.) Proteins do most of the work of the cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 54

Structure and Function of the Nucleus
The nucleus is separated from the cytoplasm by a double membrane called the nuclear envelope. Pores in the envelope allow materials to move between the nucleus and cytoplasm. The nucleus contains a nucleolus where ribosomes are made. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 55

Chromatin fiber Nuclear envelope Ribosomes Nucleolus
Figure 4.8 Chromatin fiber Nuclear envelope Ribosomes Nucleolus Nuclear pore TEM TEM Surface of nuclear envelope Nuclear pores Figure 4.8 The nucleus

Chromatin fiber Nuclear envelope
Figure 4.8a Chromatin fiber Nuclear envelope Ribosomes Nucleolus Nuclear pore Figure 4.8 The nucleus (detail)

Surface of nuclear envelope
Figure 4.8b TEM Surface of nuclear envelope Figure 4.8 The nucleus (TEM 1)

Figure 4.8c TEM Nuclear pores Figure 4.8 The nucleus (TEM 2)

Structure and Function of the Nucleus
Stored in the nucleus are long DNA molecules and associated proteins that form fibers called chromatin. Chromatin is a long stretch of a DNA molecule with proteins attached which help package the DNA into a chromosome. Each long chromatin fiber constitutes one chromosome. The number of chromosomes in a cell depends on the species. Humans have 23 pairs of chromosomes. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 60

DNA molecule Proteins Chromatin fiber Chromosome Figure 4.9
Figure 4.9 The relationship between DNA, chromatin, and a chromosome

Ribosomes Ribosomes are responsible for protein synthesis.
Ribosome components are made in the nucleolus but assembled in the cytoplasm. They are free ribosomes if the do their work in the cytoplasm of the cell. Free ribosomes will synthesize proteins that are free in the cytoplasm. They are bound ribosomes if they are attached to the nuclear membrane or the rough endoplasmic reticulum. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 62

Ribosomes They are bound ribosomes if they are attached to the nuclear membrane or the rough endoplasmic reticulum. Proteins synthesized by bound ribosomes are placed in the membranes of the organelles or secreted to the outside of the cell. © 2013 Pearson Education, Inc.

Ribosome mRNA Protein Figure 4.10
Figure 4.10 A computer model of a ribosome synthesizing a protein

Ribosomes Ribosomes may synthesize proteins while the ribosomes are
suspended in the fluid of the cytoplasm or attached to the outside of the nucleus or an organelle called the rough endoplasmic reticulum. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 65

Ribosomes in cytoplasm Ribosomes attached to endoplasmic reticulum
Figure 4.11 TEM Ribosomes in cytoplasm Ribosomes attached to endoplasmic reticulum Figure 4.11 The locations of ribosomes (TEM)

How DNA Directs Protein Production
DNA programs protein production in the cytoplasm by transferring its coded information into messenger RNA (mRNA). Messenger RNA exits the nucleus through pores in the nuclear envelope. A ribosome moves along the mRNA, translating the genetic message into a protein with a specific amino acid sequence. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often enter college with misunderstandings about the interrelationship between DNA, a chromosome, and a replicated chromosome often photographed just prior to mitosis or meiosis. Consider specifically distinguishing between these important cellular components early in your discussions of the nucleus. 2. Noting the main flow of genetic information from DNA to RNA to protein on the board will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, RNA, and proteins are produced in a cell. Teaching Tips 1. Some of your more knowledgeable students may like to guess the exceptions to 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and red blood cells in non-fetal mammals. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the doors to the boss’s office. 3. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary “working copy” of the genetic material. In some ways, this is similar to making a working photocopy of an important document, keeping the original copy safely stored away. 4. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) 67

1 DNA Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm
Figure DNA 1 Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm Figure 4.12 DNA  RNA  Protein (step 1)

1 2 DNA Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm mRNA
Figure DNA 1 Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm 2 mRNA Movement of mRNA into cytoplasm via nuclear pore Figure 4.12 DNA  RNA  Protein (step 2)

1 2 3 DNA Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm mRNA
Figure DNA 1 Synthesis of mRNA in the nucleus mRNA Nucleus Cytoplasm 2 mRNA Movement of mRNA into cytoplasm via nuclear pore Ribosome 3 Synthesis of protein in the cytoplasm Protein Figure 4.12 DNA  RNA  Protein (step 3)

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS
The cytoplasm of a eukaryotic cell is partitioned by organelle membranes. This system of membranes includes the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes and vacuoles Many membranous organelles forming the endomembrane system in a cell are interconnected either directly by their membranes or by transfer of membrane segments between them. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 71

The Endoplasmic Reticulum
The endoplasmic reticulum (ER) is one of the main manufacturing facilities in a cell. The ER produces an enormous variety of molecules, is connected to the nuclear envelope is labyrinth of sacs and tubes running throughout the cytosplasm, and is composed of smooth and rough ER. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 72

Nuclear envelope Ribosomes Rough ER Smooth ER Ribosomes Figure 4.13
TEM Ribosomes Figure 4.13 The endoplasmic reticulum (ER)

Nuclear envelope Ribosomes Rough ER Smooth ER Figure 4.13a
Figure 4.13 The endoplasmic reticulum (ER) (detail)

Rough ER Smooth ER Ribosomes TEM Figure 4.13b
Figure 4.13 The endoplasmic reticulum (ER) (TEM)

These ribosomes produce membrane proteins and secretory proteins.
Rough ER The “rough” in rough ER refers to ribosomes that stud the outside of this portion of the ER membrane. These ribosomes produce membrane proteins and secretory proteins. Phospholipids made by enzymes of the rough ER are inserted into the ER membrane. In this way, the ER membrane grows, and portions of it are transferred to other parts of the cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 76

Rough ER The ribosomes attached to the rough ER produce proteins that will be inserted into the growing ER membrane, transported to other organelles, and eventually exported from the cell. Cells that secrete a lot of protein – such as cells of your salivary glands, which secrete enzymes into your mouth – are especially rich in rough ER. © 2013 Pearson Education, Inc.

Rough ER Some products manufactured by rough ER are dispatched to other locations in the cell by transport vesicles, sacs made of membrane that bud off from the rough ER. © 2013 Pearson Education, Inc.

Vesicles bud off from the ER.
Figure 4.14 Secretory proteins depart. Vesicles bud off from the ER. Proteins are modified in the ER. Transport vesicle Ribosome A ribosome links amino acids. Protein Rough ER Polypeptide Figure 4.14 How rough ER manufactures and packages secretory proteins

Smooth ER The smooth ER lacks surface ribosomes,
have a diversity of enzymes built into the membrane that perform a variety of functions produces lipids including steroids (ovaries and testes are rich in smooth ER) © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 80

Smooth ER The smooth ER in liver cells enzymes of the smooth ER detoxify sedative drugs such as barbituates; stimulants such as amphetamines and some antibiotics. as liver cells are exposed to a drug, the amounts of smooth ER and the detoxifying enzymes increase this can increase tolerance to a drug meaning more drug will need to be given for the same effect Increased tolerance of drugs is one of the hallmarks of addiction © 2013 Pearson Education, Inc.

The Golgi Apparatus The Golgi apparatus
works in partnership with the ER and receives, refines, stores, and distributes chemical products of the cell. Products made in the ER reach the Golgi apparatus in transport vesicles. The Golgi apparatus consists of a stack of hollow membrane plates © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 82

The Golgi Apparatus One side (the receiving side) receives packages from the ER via transport vesicles Proteins within the vesicle are usually chemically modified by enzymes during their transit from the “receiving side” to the “shipping side” For example, proteins may be “tagged” for identification to be sent to a certain part of the cell. The “shipping side” is a depot from which finished products can be carried in transport vesicles or to the plasma membrane. © 2013 Pearson Education, Inc.

“Receiving” side of the
Figure 4.15 “Receiving” side of the Golgi apparatus Transport vesicle from rough ER “Receiving” side of the Golgi apparatus 1 New vesicle forming 2 Transport vesicle from the Golgi apparatus 3 Colorized SEM “Shipping” side of the Golgi apparatus Plasma membrane New vesicle forming Figure 4.15 The Golgi apparatus

Transport vesicle from rough ER “Receiving” side of
Figure 4.15a Transport vesicle from rough ER “Receiving” side of the Golgi apparatus 1 New vesicle forming 2 Transport vesicle from the Golgi apparatus 3 “Shipping” side of the Golgi apparatus Plasma membrane Figure 4.15 The Golgi apparatus (detail)

“Receiving” side of the
Figure 4.15b “Receiving” side of the Golgi apparatus Colorized SEM New vesicle forming Figure 4.15 The Golgi apparatus (SEM)

Lysosomes A lysosome is a membrane-bound sac of digestive enzymes found in animal cells. Lysosomes are absent from most plant cells. Lysosomes develop from vesicles that bud off from the Golgi apparatus Enzymes in a lysosome can break down large molecules such as proteins, polysaccharides, fats, and nucleic acids. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 87

Lysosomes Lysosomes have several types of digestive functions.
Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles. These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food. Small molecules from digestion leave the lysosome and nourish the cell. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 88

Lysosomes The lysosome provides a safe compartment where the cell can digest these molecules safely, without unleashing these digestive enzymes on the rest of the cell. They have several digestive functions. Many engulf nutrients into tiny cytoplasmic sacs called food vacuoles. Lysosomes fuse with the food vacuoles, exposing the food molecules to enzymes that digest them. © 2013 Pearson Education, Inc.

Lysosomes Lysosomes also help to destroy harmful viruses and bacteria. For example: our white blood cells ingest bacteria into vacuoles and lysosomal enzymes emptied into these vacuoles rupture the bacterial cell walls. In addition, lysosomes break down the large molecules of damaged organelles, acting as a recycler of materials © 2013 Pearson Education, Inc.

Lysosomes There are lysosome storage diseases.
A person with such a disease is lacking one or more of the digestive enzymes The abnormal lysosome becomes engorged with molecules making it unable to function. In Tay-Sachs disease, lysosomes lack lipid digesting enzymes resulting in nerve cell death causing great harm to the nervous system. © 2013 Pearson Education, Inc.

(a) A lysosome digesting food
Figure 4.16 Plasma membrane Digestive enzymes Lysosome Lysosome Digestion Digestion Food vacuole Vesicle containing damaged organelle (a) A lysosome digesting food (b) A lysosome breaking down the molecules of damaged organelles Organelle fragment Vesicle containing two damaged organelles Organelle fragment TEM Figure 4.16 Two functions of lysosomes

(a) A lysosome digesting food
Figure 4.16a Plasma membrane Digestive enzymes Lysosome Digestion Food vacuole (a) A lysosome digesting food Figure 4.16 Two functions of lysosomes (part 1)

(b) A lysosome breaking down the molecules of damaged organelles
Figure 4.16b Lysosome Digestion Vesicle containing damaged organelle (b) A lysosome breaking down the molecules of damaged organelles Figure 4.16 Two functions of lysosomes (part 2)

Vesicle containing two damaged organelles
Figure 4.16c Organelle fragment Vesicle containing two damaged organelles Organelle fragment TEM Figure 4.16 Two functions of lysosomes (TEM)

Vacuoles Vacuoles are large sacs of membrane that bud from the ER,
Golgi apparatus, or plasma membrane. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students might have trouble connecting the diverse functions to the organelles. The pathway of secretory proteins is a good process to use to introduce the primary organelle functions. The movement of information and products extends generally from the central nucleus to the interconnected rough ER, to the more peripherally located Golgi, and finally to the outer plasma membrane. Introducing the steps of this process with the central to peripheral flow may help students better see the interrelationships and recall the sequence. 2. Conceptually, some students seem to benefit from the well-developed factory-like-a-cell analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. Teaching Tips 1. The endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. 2. Students often learn that a human body can build up a tolerance to a drug. Here in chapter 4, students learn about one of the specific mechanisms of this response. Liver cells exposed to certain toxins or drugs increase the amount of smooth ER, which functions in the processing of these chemicals. Thus, there is a structural and functional explanation to the development of drug tolerance. 3. Some people think the Golgi apparatus looks like a stack of pita bread. 4. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory. 5. Lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” 96

Vacuoles Vacuoles have a variety of functions.
A food vacuole can store food for the host cell. Certain freshwater protists have contractile vacuoles that pump out excess water that flows into the cell from the outside environment. Another type is called a central vacuole, which can account for more than half of the volume of a plant cell. It can store proteins such as those found in seed cells. It can store colorful pigments in cells of flower petals to attract pollinators. It may also store poisons that protect a plant against plant-eating animals. © 2013 Pearson Education, Inc.

(a) Contractile vacuole in Paramecium
Figure 4.17a A vacuole filling with water LM A vacuole contracting LM (a) Contractile vacuole in Paramecium Figure 4.17 Two types of vacuoles (part 1)

(b) Central vacuole in a plant cell
Figure 4.17b Colorized TEM Central vacuole (b) Central vacuole in a plant cell Figure 4.17 Two types of vacuoles (part 2)

The Endomembrane System
The following figure will help you to review how organelles of the endomembrane system are related and work together. Note that a product made in one part of the endomembrane system may exit the cell entirely OR become part of another organelle. Also note that membrane made by ER can become part of the plasma membrane through the fusion of a transport vesicle. In this way, the plasma membrane is related to the endomembrane system. © 2013 Pearson Education, Inc.

Transport vesicles carry enzymes and
Figure 4.18 Rough ER Golgi apparatus Transport vesicle Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Plasma membrane Lysosomes carrying digestive enzymes can fuse with other vesicles. Golgi apparatus Secretory protein TEM Some products are secreted from the cell. Vacuoles store some cell products. New vesicle forming Transport vesicle from the Golgi apparatus Plasma membrane Figure 4.18 Review of the endomembrane system

Rough ER Golgi apparatus Transport vesicle Transport vesicles
Figure 4.18a Rough ER Golgi apparatus Transport vesicle Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Plasma membrane Lysosomes carrying digestive enzymes can fuse with other vesicles. Secretory protein Some products are secreted from the cell. Vacuoles store some cell products. Figure 4.18 Review of the endomembrane system (detail)

Transport vesicle from the Golgi apparatus
Figure 4.18b Golgi apparatus TEM New vesicle forming Transport vesicle from the Golgi apparatus Plasma membrane Figure 4.18 Review of the endomembrane system (TEM)

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION
Cells require a continuous energy supply to perform the work of life. Two organelles act as cellular power stations: chloroplasts and mitochondria. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 104

Chloroplasts Most of the living world runs on the energy provided by photosynthesis. Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar and other organic molecules. Chloroplasts are unique to the photosynthetic cells of plants and algae and the organelles that perform photosynthesis. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 105

Chloroplasts Chloroplasts are divided into three major compartments by internal membranes: the space between the two membranes, the inter-membrane space the stroma, a thick fluid within the chloroplast Disc-like compartments called thylakoids; the thylakoids are arranged in stacks called grana © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 106

Stroma (fluid in chloroplast)
Figure 4.19a Inner and outer membranes Granum Space between membranes Stroma (fluid in chloroplast) Figure 4.19 The chloroplast: site of photosynthesis (detail)

Stroma (fluid in chloroplast)
Figure 4.19b Stroma (fluid in chloroplast) Granum TEM Figure 4.19 The chloroplast: site of photosynthesis (TEM)

Mitochondria Mitochondria are the organelles of cellular respiration,
are found in almost all eukaryotic cells, and produce ATP (Adenosine triphosphate – the energy molecules of cells) from the energy of food molecules. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 110

Mitochondria An envelope of two membranes encloses the mitochondrion:
an outer smooth membrane and an inner membrane that has numerous infoldings called cristae and encloses a thick fluid called the matrix. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 111

Outer membrane Inner membrane Cristae Matrix Space between membranes
Figure 4.20 Outer membrane TEM Inner membrane Cristae Matrix Space between membranes Figure 4.20 The mitochondrion: site of cellular respiration

Figure 4.20a Outer membrane Inner membrane Cristae Matrix Space between membranes Figure 4.20 The mitochondrion: site of cellular respiration (detail)

Figure 4.20b Outer membrane TEM Inner membrane Cristae Matrix Space between membranes Figure 4.20 The mitochondrion: site of cellular respiration (TEM)

Mitochondria Mitochondria and chloroplasts contain their own DNA, which encodes some of their proteins. This DNA is evidence that mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They may falsely think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and “spent” in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. This makes sense when we consider that the outer membranes correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Biology makes sense in light of evolution. 3. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. 115

THE CYTOSKELETON: CELL SHAPE AND MOVEMENT
The cytoskeleton is a network of fibers extending throughout the cytoplasm. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 116

Maintaining Cell Shape
The cytoskeleton provides mechanical support to the cell helps a cell maintain its shape allows organelles (such as transport vesicles) to move around the cell © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 117

The cytoskeleton contains several types of fibers made from different proteins: Microtubules are straight and hollow tubes that guide the movement of organelles and chromosomes. Intermediate filaments and microfilaments are thinner and solid. The cytoskeleton provides anchorage and reinforcement for many organelles. For instance, the nucleus is held in place by a cytoskeletal cage of filaments. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 118

The microtubules form tiny “streets” that organelles can hold onto to move from one area to another. E.g. a lysosome might reach a food vacuole by taking many small “baby steps” along a microtubule tract. Microtubules also guide the movement of chromosomes when a cell undergoes cell division © 2013 Pearson Education, Inc.

The cytoskeleton is dynamic. Changes in the cytoskeleton contribute to the amoeboid (crawling) movements of the protist Amoeba and some of our white blood cells. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 120

(a) Microtubules in the cytoskeleton
Figure 4.21a LM (a) Microtubules in the cytoskeleton Figure 4.21 The cytoskeleton (part 1)

(b) Microtubules and movement
Figure 4.21b LM (b) Microtubules and movement Figure 4.21 The cytoskeleton (part 2)

Cilia and Flagella In some cells, microtubules are arranged into cilia and flagella Cilia and flagella are motile appendages that aid in movement. Flagella propel the cell through their undulating, whiplike motion. They often occur singly such as in the sperm cells of humans and other animals. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 123

Cilia and Flagella Cilia and flagella have the same basic architecture, but cilia are generally shorter and more numerous than flagella. Both cilia and flagella propel various protists through the water. Though different in number, length and beating pattern, they both have the same basic architecture with a core of microtubules wrapped in the extension of a plasma membrane.

Cilia and Flagella Some cilia extend from nonmoving cells that are part of the surface layer of a tissue. There, they can move fluid over the tissue’s surface. For example, cilia lining your trachea (windpipe) constantly clean your respiratory surface by sweeping mucus with trapped debris out of your lungs. Tobacco smoke can inhibit and destroy these cilia

Cilia and Flagella Some men who have problems with their sperm flagella also suffer from respiratory problems. The explanation lies in the similarities between flagella and cilia. Because of a defect in these structures, their sperm cannot swim normally within the female to fertilize the egg and their cilia cannot sweep mucus out of their lungs.

(a) Flagellum of a human sperm cell
Figure 4.22 Colorized SEM Colorized SEM (a) Flagellum of a human sperm cell (b) Cilia on a protist (c) Cilia lining the respiratory tract Colorized SEM Figure 4.22 Examples of flagella and cilia

(a) Flagellum of a human sperm cell
Figure 4.22a (a) Flagellum of a human sperm cell Colorized SEM Figure 4.22 Examples of flagella and cilia (part 1)

(b) Cilia on a protist Colorized SEM Figure 4.22b
Figure 4.22 Examples of flagella and cilia (part 2)

(c) Cilia lining the respiratory tract
Figure 4.22c Colorized SEM (c) Cilia lining the respiratory tract Figure 4.22 Examples of flagella and cilia (part 3)

https://www. youtube. com/watch. v=1Z9pqST72is A Tour of the Cell (14
A Tour of the Cell (14.16) Cell Structure and Function (9.06) Animal Cells (11.34) Plant Cells (10.27) Cell Organelles Part 1 (12.57)

Evolution Connection: The Evolution of Antibiotic Resistance
Many antibiotics disrupt cellular structures of invading microorganisms. Introduced in the 1940s, penicillin worked well against such infections. But over time, bacteria that were resistant to antibiotics, such as the MRSA strain, were favored. The widespread use and abuse of antibiotics continue to favor bacteria that resist antibiotics. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than cell broth, a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. 2. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. (See also Teaching Tip 1 below.) 3. The dynamic, weblike structure of the cytoskeleton is very different from the skeletons that students may already know. Their dynamic structures (see Teaching Tip 2 below) are quite unlike any human designs. Students have much to gain from vivid illustrations of cytoskeletal diversity. Consider sharing some impressive images from a Google image search or other resources. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! 2. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have their structural framework routinely constructed, deconstructed, and then re-formed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then re-formed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies. 132

Figure 4.23 Figure 4.23 The changing role of antibiotics

Figure 4.23a Figure 4.23 The changing role of antibiotics (part 1)

Figure 4.23b Figure 4.23 The changing role of antibiotics (part 2)

Figure 4.UN01 Figure 4.UN01 In-text figure, the plasma membrane, p. 60

Figure 4.UN02 Figure 4.UN02 In-text figure, the nucleus, p. 62

Figure 4.UN03 Figure 4.UN03 In-text figure, ribosomes, p. 63

Figure 4.UN04 Figure 4.UN04 In-text figure, the endoplasmic reticulum, p. 64

Figure 4.UN05 Figure 4.UN05 In-text figure, the golgi apparatus, p. 65

Figure 4.UN06 Figure 4.UN06 In-text figure, lysosomes, p. 66

Figure 4.UN07 Figure 4.UN07 In-text figure, vacuoles, p. 67

Figure 4.UN08 Figure 4.UN08 In-text figure, chloroplasts, p. 68

Figure 4.UN09 Figure 4.UN09 In-text figure, mitochondria, p. 68

Figure 4.UN10 Figure 4.UN10 In-text figure, the cytoskeleton, p. 69

CATEGORIES OF CELLS Prokaryotic Cells Eukaryotic Cells • Smaller
Figure 4.UN11 CATEGORIES OF CELLS Prokaryotic Cells Eukaryotic Cells • Smaller • Simpler • Most do not have organelles • Found in bacteria and archaea • Larger • More complex • Have organelles • Found in protists, plants, fungi, animals Figure 4.UN11 Summary of Key Concepts: The Two Major Categories of Cells

Cytoplasm (inside of cell)
Figure 4.UN12 Outside of cell Phospholipid Hydrophilic Protein Hydrophobic Hydrophilic Cytoplasm (inside of cell) Figure 4.UN12 Summary of Key Concepts: The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins

Chemical energy (food) CELLULAR RESPIRATION
Figure 4.UN13 Mitochondrion Chloroplast Light energy Chemical energy (food) CELLULAR RESPIRATION PHOTOSYNTHESIS ATP Figure 4.UN13 Summary of Key Concepts: Chloroplasts and Mitochondria

Chapter 4 A Tour of the Cell.

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