Chapter 4 A Tour of the Cell By Mousumi Goswami.

Chapter 4 A Tour of the Cell By Mousumi Goswami

Biology and Society: Drugs That Target Bacterial Cells
Antibiotics were first isolated from mold in 1928. The widespread use of antibiotics drastically decreased deaths from bacterial infections. © 2010 Pearson Education, Inc.

Bacteria on human skin cells
Figure 4.0

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.

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 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Microscopes as Windows on the World 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 Lenses enlarge, or magnify, the image 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

(for viewing living cells)
Light Micrograph (LM) (for viewing living cells) LM Light micrograph of a protist, Paramecium Figure 4.1a Types of micrographs (LM)

Magnification is an increase in the specimen’s apparent size.
Resolving power is the ability of an optical instrument to show two objects as separate. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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.
The accumulation of scientific evidence led to the cell theory. All living things are composed of cells. All cells come from other cells. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Two kinds of electron microscopes reveal different parts of cells.
The electron microscope (EM) uses a beam of electrons, which results in better resolving power than the light microscope. Two kinds of electron microscopes reveal different parts of cells. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Scanning Electron Micrograph (SEM) (for viewing surface features)
Colorized SEM Scanning electron micrograph of Paramecium Figure 4.1b Figure 4.1b Types of micrographs (SEM)

Transmission Electron Micrograph (TEM)
(for viewing internal structures) Colorized TEM Transmission electron micrograph of Paramecium Figure 4.1c Figure 4.1c Types of micrographs (TEM)

The electron microscope can
Magnify up to 100,000 times Distinguish between objects 0.2 nanometers apart 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Figure 4.2 Electron microscope

Figure 4.1 Types of micrographs
Light Micrograph (LM) (for viewing living cells) Scanning Electron Micrograph (SEM) (for viewing surface features) Transmission Electron Micrograph (TEM) (for viewing internal structures) LM Colorized SEM Colorized TEM Light micrograph of a protist, Paramecium Scanning electron micrograph of Paramecium Transmission electron micrograph of Paramecium Figure 4.1 Types of micrographs

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

The Two Major Categories of Cells
The countless cells on earth fall into two categories: Prokaryotic cells — Bacteria and Archaea Eukaryotic cells — plants, fungi, and animals All cells have several basic features. They are all bound by a thin plasma membrane. All cells have DNA and ribosomes, tiny structures that build proteins. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Prokaryotic and eukaryotic cells have important differences.
Prokaryotic cells are older than eukaryotic cells. Prokaryotes appeared about 3.5 billion years ago. Eukaryotes appeared about 2.1 billion years ago. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Prokaryotes Are smaller than eukaryotic cells
Lack internal structures surrounded by membranes Lack a nucleus Have a rigid cell wall 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Eukaryotes Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions. The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

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

An Overview of Eukaryotic Cells
Eukaryotic cells are fundamentally similar. The region between the nucleus and plasma membrane is the cytoplasm. The cytoplasm consists of various organelles suspended in fluid. 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Unlike animal cells, plant cells have
Protective cell walls Chloroplasts, which convert light energy to the chemical energy of food 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 alternate 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 technology that has 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 detect or magnify wavelengths beyond our vision, etc. Students could 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, etc. 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 a SEM—both rely upon 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 relationship between a meter and a millimeter is the same as a millimeter is to a micron. Each is a difference of 1000. 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: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) 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 below. 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

Ribosomes Centriole Not in most plant cells Lysosome Cytoskeleton
Flagellum Plasma membrane Nucleus Mitochondrion Rough endoplasmic reticulum (ER) Smooth endoplasmic reticulum (ER) Golgi apparatus Idealized animal cell Figure 4.5a A view of an idealized animal cell

Cytoskeleton Central vacuole Mitochondrion Not in animal cells
Cell wall Nucleus Chloroplast Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic reticulum (ER) Channels between cells Golgi apparatus Idealized plant cell Figure 4.5b A view of an idealized plant cell

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 UN12 Summary: categories of cells

MEMBRANE STRUCTURE The plasma membrane separates the living cell from its nonliving surroundings. The membranes of cells are composed mostly of Lipids Proteins The lipids belong to a special category called phospholipids. Phospholipids form a two-layered membrane, the phospholipid bilayer. 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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) Cytoplasm (inside of cell)
Outside of cell Outside of cell Proteins Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophilic head Phospholipid bilayer Hydrophobic tail Phospholipid Cytoplasm (inside of cell) (a) Phospholipid bilayer of membrane Hydrophobic regions of protein Cytoplasm (inside of cell) (b) Fluid mosaic model of membrane Figure 4.6 Plasma membrane structure

The plasma membrane is a fluid mosaic:
Most membranes have specific proteins embedded in the phospholipid bilayer. These proteins help regulate traffic across the membrane and perform other functions. The plasma membrane is a fluid mosaic: Fluid because molecules can move freely past one another A mosaic because of the diversity of proteins in the membrane 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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 Process of Science: What Makes a Superbug?
Observation: Bacteria use a protein called PSM to disable human immune cells by forming holes in 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. 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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.)

Experiment: Researchers infected
Seven mice with normal MRSA 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. 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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.)

Conclusions: MRSA strains appear to use the membrane-destroying PSM protein, but Factors other than PSM protein contributed to the death of mice 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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.)

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

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

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

Cell Surfaces Plant cells have rigid cell walls surrounding the membrane. Plant cell walls Are made of cellulose Protect the cells Maintain cell shape Keep the cells from absorbing too much water 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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.)

Animal cells Lack cell walls Have an extracellular matrix, which Helps hold cells together in tissues Protects and supports them The surfaces of most animal cells contain cell junctions, structures that connect to other cells. 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, both membranes and our skin detect stimuli, engage in gas exchange, and 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 NUCLEUS AND RIBOSOMES: GENETIC CONTROL OF THE CELL
The nucleus is the chief executive of the cell. Genes in the nucleus store information necessary to produce proteins. Proteins do most of the work of the cell. © 2010 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

Structure and Function of the Nucleus
The nucleus is bordered 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. Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

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

Each long chromatin fiber constitutes one chromosome.
Stored in the nucleus are long DNA molecules and associated proteins that form fibers called chromatin. Each long chromatin fiber constitutes one chromosome. The number of chromosomes in a cell depends on the species. Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

DNA molecule Chromosome
Proteins Chromatin fiber Chromosome 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. Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

Computer model of a ribosome synthesizing a protein
mRNA Protein Figure 4.10 Computer model of a ribosome synthesizing a protein

Ribosomes may assemble proteins:
Suspended in the fluid of the cytoplasm or Attached to the outside of an organelle called the endoplasmic reticulum Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

Locations of ribosomes
TEM Ribosomes in cytoplasm Ribosomes attached to endoplasmic reticulum Figure 4.11 Locations of ribosomes

How DNA Directs Protein Production
DNA directs protein production 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. Student Misconceptions and Concerns 1. 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. 2. 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.) Teaching Tips 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.

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

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

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

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS
Many membranous organelles forming the endomembrane system in a cell are interconnected either Directly or Through the transfer of membrane segments between them © 2010 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

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 composed of smooth and rough ER 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

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

Rough ER The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane. These ribosomes produce membrane proteins and secretory proteins. After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles. 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

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

Smooth ER The smooth ER Lacks surface ribosomes
Produces lipids, including steroids Helps liver cells detoxify circulating drugs 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

The Golgi Apparatus The Golgi apparatus
Works in partnership with the ER Receives, refines, stores, and distributes chemical products of the cell 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

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

Lysosomes A lysosome is a sac of digestive enzymes found in animal cells. Enzymes in a lysosome can break down large molecules such as Proteins Polysaccharides Fats Nucleic acids 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

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 Lysosomes can also Destroy harmful bacteria Break down damaged organelles 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

(a) Lysosome digesting food
Plasma membrane Digestive enzymes Lysosome Lysosome Digestion Digestion Food vacuole Vesicle containing damaged organelle (a) Lysosome digesting food (b) 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

Vacuoles Vacuoles are membranous sacs that bud from the ER Golgi
Plasma membrane 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

Contractile vacuoles of protists pump out excess water in the cell.
Central vacuoles of plants Store nutrients Absorb water May contain pigments or poisons 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

Vacuole filling with water
TEM Vacuole contracting TEM (a) Contractile vacuole in Paramecium Figure 4.17a Contractile vacuole in Paramecium

(b) Central vacuole in a plant cell
Colorized TEM (b) Central vacuole in a plant cell Figure 4.17b Central vacuole in a plant cell

To review, the endomembrane system interconnects the
Nuclear envelope ER Golgi Lysosomes Vacuoles Plasma membrane 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. Some people think the Golgi apparatus looks like a stack of pita bread. 3. If you continue the factory analogy, the addition of a molecular tag is like adding address labels in the shipping department of a factory.

Transport vesicles carry enzymes and other proteins from the rough
Rough ER Transport vesicle 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. Vacuole Secretory protein Lysosome Golgi apparatus Some products are secreted from the cell. Vacuoles store some cell products. New vesicle forming Transport vesicle from the Golgi TEM Figure 4.18 Review of the endomembrane system

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION
Cells require a constant energy supply to perform the work of life. © 2010 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 wish to emphasize the presence and significance of mitochondria and chloroplasts in plant cells. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small prokaryote size of these organelles. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. 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. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. 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.

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. Chloroplasts are the organelles that perform photosynthesis. Chloroplasts have three major compartments: The space between the two membranes The stroma, a thick fluid within the chloroplast The space within grana, the structures that trap light energy and convert it to chemical energy 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 wish to emphasize the presence and significance of mitochondria and chloroplasts in plant cells. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small prokaryote size of these organelles. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. 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. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. 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.

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

Mitochondria Mitochondria are the sites of cellular respiration, which produce ATP from the energy of food molecules. Mitochondria are found in almost all eukaryotic cells. An envelope of two membranes encloses the mitochondrion. These consist of An outer smooth membrane An inner membrane that has numerous infoldings called cristae 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 wish to emphasize the presence and significance of mitochondria and chloroplasts in plant cells. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small prokaryote size of these organelles. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. 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. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. 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.

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

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. 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 wish to emphasize the presence and significance of mitochondria and chloroplasts in plant cells. 2. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small prokaryote size of these organelles. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. 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. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. 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.

Chloroplast and Mitochondrion
Light energy Chemical energy (food) CELLULAR RESPIRATION PHOTOSYNTHESIS ATP Figure UN14 Summary: chloroplast and mitochondrion

THE CYTOSKELETON: CELL SHAPE AND MOVEMENT
The cytoskeleton is a network of fibers extending throughout the cytoplasm. The cytoskeleton contains several types of fibers made from different proteins: Microtubules Are straight and hollow Guide the movement of organelles and chromosomes Intermediate filaments and microfilaments are thinner and solid The cytoskeleton Provides mechanical support to the cell Maintains its shape © 2010 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than a watery fluid, which 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 instead covered by mucus. Cilia lining our trachea do not reach the air to comb it. Instead, these cilia sweep the dirty mucus up our respiratory tracts. (See also Teaching Tip #2 below.) 3. The dynamic, web-like 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 amongst 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 reformed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reformed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies.

(a) Microtubules in the cytoskeleton (b) Microtubules and movement
LM (a) Microtubules in the cytoskeleton (b) Microtubules and movement LM Figure 4.21 The cytoskeleton

The cytoskeleton is dynamic.
Changes in the cytoskeleton contribute to the amoeboid motion of an Amoeba. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than a watery fluid, which 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 instead covered by mucus. Cilia lining our trachea do not reach the air to comb it. Instead, these cilia sweep the dirty mucus up our respiratory tracts. (See also Teaching Tip #2 below.) 3. The dynamic, web-like 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 amongst 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 reformed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reformed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies.

Cilia and Flagella Cilia and flagella aid in movement.
Flagella propel the cell in a whiplike motion. Cilia move in a coordinated back-and-forth motion. Cilia and flagella have the same basic architecture. Cilia may extend from nonmoving cells. On cells lining the human trachea, cilia help sweep mucus out of the lungs. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than a watery fluid, which 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 instead covered by mucus. Cilia lining our trachea do not reach the air to comb it. Instead, these cilia sweep the dirty mucus up our respiratory tracts. (See also Teaching Tip #2 below.) 3. The dynamic, web-like 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 amongst 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 reformed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reformed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies.

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

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 were favored. The widespread use and abuse of antibiotics continues to favor bacteria that resist antibiotics. © 2010 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often regard the fluid of the cytoplasm as little more than a watery fluid, which 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 instead covered by mucus. Cilia lining our trachea do not reach the air to comb it. Instead, these cilia sweep the dirty mucus up our respiratory tracts. (See also Teaching Tip #2 below.) 3. The dynamic, web-like 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 amongst 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 reformed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reformed repeatedly but typically rely upon the same basic design.) Thus, caution is especially warranted in such analogies.

Figure 4.23 The changing role of antibiotics

Cytoplasm (inside of cell)
Outside of cell Phospholipid Hydrophilic Protein Hydrophobic Hydrophilic Cytoplasm (inside of cell) Figure 4.UN13 Figure UN13 Summary: plasma membrane

Chapter 4 A Tour of the Cell By Mousumi Goswami.

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Chapter 4 A Tour of the Cell By Mousumi Goswami.

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