Introduction – Chapter 4 Cells are the simplest collection of matter that can live. Cells were first observed by Robert Hooke in 1665. Working with more refined lenses, Antoni van Leeuwenhoek later described blood, sperm, and organisms living in pond water. © 2012 Pearson Education, Inc. 1

Introduction Since the days of Hooke and Leeuwenhoek, improved microscopes have vastly expanded our view of the cell. © 2012 Pearson Education, Inc. 2

Introduction to the Cell The Nucleus and Ribosomes Figure 4.0_1 Chapter 4: Big Ideas Introduction to the Cell The Nucleus and Ribosomes Figure 4.0_1 Chapter 4: Big Ideas The Endomembrane System Energy-Converting Organelles The Cytoskeleton and Cell Surfaces 3

Figure 4.0_2 Figure 4.0_2 Cancer cells 4

4.1 Microscopes reveal the world of the cell A variety of microscopes have been developed for a clearer view of cells and cellular structure. The most frequently used microscope is the light microscope (LM)—like the one used in biology laboratories. Light passes through a specimen, then through glass lenses, and finally light is projected into the viewer’s eye. Specimens can be magnified up to 1,000 times the actual size of the specimen. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 5

4.1 Microscopes reveal the world of the cell Magnification is the increase in the apparent size of an object. Resolution is a measure of the clarity of an image. In other words, it is the ability of an instrument to show two close objects as separate. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 6

4.1 Microscopes reveal the world of the cell Microscopes have limitations. The human eye and the microscope have limits of resolution—the ability to distinguish between small structures. Therefore, the light microscope cannot provide the details of a small cell’s structure. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 7

4.1 Microscopes reveal the world of the cell Using light microscopes, scientists studied microorganisms, animal and plant cells, and some structures within cells. In the 1800s, these studies led to cell theory, which states that all living things are composed of cells and all cells come from other cells. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 8

Figure 4.1A Figure 4.1A Light micrograph of a protist, Paramecium 9

Figure 4.1B The size range of cells and related objects 10 m Human height 1 m Length of some nerve and muscle cells 100 mm (10 cm) Chicken egg Unaided eye 10 mm (1 cm) Frog egg 1 mm Paramecium Human egg 100 m Most plant and animal cells Light microscope 10 m Nucleus Most bacteria Mitochondrion 1 m Figure 4.1B The size range of cells and related objects Smallest bacteria Electron microscope 100 nm Viruses Ribosome 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms 10

4.1 Microscopes reveal the world of the cell Beginning in the 1950s, scientists started using a very powerful microscope called the electron microscope (EM) to view the ultrastructure of cells. Instead of light, EM uses a beam of electrons. Electron microscopes can resolve biological structures as small as 2 nanometers and magnify up to 100,000 times. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 11

4.1 Microscopes reveal the world of the cell Scanning electron microscopes (SEM) study the detailed architecture of cell surfaces. Transmission electron microscopes (TEM) study the details of internal cell structure. Differential interference light microscopes amplify differences in density so that structures in living cells appear almost three-dimensional. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of 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 and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance 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 electron microscopes. Dissection microscopes are like an 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 same way a compound light microscope or TEM works! © 2012 Pearson Education, Inc. 12

Figure 4.1C Figure 4.1C Scanning electron micrograph of Paramecium 13

Figure 4.1D Figure 4.1D Transmission electron micrograph of Toxoplasma 14

Figure 4.1E Figure 4.1E Differential interference contrast micrograph of Paramecium 15

4.2 The small size of cells relates to the need to exchange materials across the plasma membrane Cell size must be large enough to house DNA, proteins, and structures needed to survive and reproduce, but remain small enough to allow for a surface-to-volume ratio that will allow adequate exchange with the environment. 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.) 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 2. Here is another way to explain surface-to-volume ratios. Have your class consider this situation. You purchase a set of eight coffee mugs, each in its own cubic box, for a wedding present. You can wrap the eight boxes together as one large cube, or wrap each of the eight boxes separately. Either way, you will be wrapping the same volume. However, wrapping the mugs separately requires much more paper. This is because the surface-to-volume ratio is greater for smaller objects. 3. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Furthermore, because of these hydrophobic properties, lipid bilayers are also self-healing. That the properties of phospholipids emerge from their organization is worth emphasizing to students. 4. You might wish to share a very simple analogy that works very well for 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 by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 16

Surface-to- volume ratio 2 6 Figure 4.2A 1 3 1 3 Total volume 27 units3 27 units3 Figure 4.2A Effect of cell size on surface area Total surface area 54 units2 162 units2 Surface-to- volume ratio 2 6 17

4.2 The small size of cells relates to the need to exchange materials across the plasma membrane The plasma membrane forms a flexible boundary between the living cell and its surroundings. Phospholipids form a two-layer sheet called a phospholipid bilayer in which hydrophilic heads face outward, exposed to water, and hydrophobic tails point inward, shielded from 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.) 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 2. Here is another way to explain surface-to-volume ratios. Have your class consider this situation. You purchase a set of eight coffee mugs, each in its own cubic box, for a wedding present. You can wrap the eight boxes together as one large cube, or wrap each of the eight boxes separately. Either way, you will be wrapping the same volume. However, wrapping the mugs separately requires much more paper. This is because the surface-to-volume ratio is greater for smaller objects. 3. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Furthermore, because of these hydrophobic properties, lipid bilayers are also self-healing. That the properties of phospholipids emerge from their organization is worth emphasizing to students. 4. You might wish to share a very simple analogy that works very well for 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 by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 18

Membrane proteins are either 4.2 The small size of cells relates to the need to exchange materials across the plasma membrane Membrane proteins are either attached to the membrane surface or embedded in the phospholipid bilayer. Some proteins form channels or tunnels that shield ions and other hydrophilic molecules as they pass through the hydrophobic center of the membrane. Other proteins serve as pumps, using energy to actively transport molecules into or out of the cell. 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.) 2. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter to a micron: 1,000 to 1. 2. Here is another way to explain surface-to-volume ratios. Have your class consider this situation. You purchase a set of eight coffee mugs, each in its own cubic box, for a wedding present. You can wrap the eight boxes together as one large cube, or wrap each of the eight boxes separately. Either way, you will be wrapping the same volume. However, wrapping the mugs separately requires much more paper. This is because the surface-to-volume ratio is greater for smaller objects. 3. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Furthermore, because of these hydrophobic properties, lipid bilayers are also self-healing. That the properties of phospholipids emerge from their organization is worth emphasizing to students. 4. You might wish to share a very simple analogy that works very well for 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 by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 19

Hydrophobic region of a protein Figure 4.2B Outside cell Hydrophilic heads Hydrophobic region of a protein Hydrophobic tails Hydrophilic region of a protein Phospholipid Figure 4.2B A plasma membrane: a phospholipid bilayer with associated proteins Inside cell Channel protein Proteins 20

4.3 Prokaryotic cells are structurally simpler than eukaryotic cells Bacteria and archaea are prokaryotic cells. All other forms of life are composed of eukaryotic cells. Prokaryotic and eukaryotic cells have a plasma membrane and one or more chromosomes and ribosomes. Eukaryotic cells have a membrane-bound nucleus and number of other organelles. Prokaryotes have a nucleoid and no true organelles. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. A visual comparison of prokaryotic and eukaryotic cells, such as that found in Figure 1.3, can be very helpful when discussing the key differences between these cell types. These cells are strikingly different in size and composition. Providing students with a visual reference point rather than simply listing these traits will help them better retain this information. 2. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter of a factor of ten translates into a much greater difference in volume. If students recall enough geometry, you may want to challenge them to calculate the difference in the volume of two cells with diameters that differ by a factor of ten (the answer is about 1,000). 3. 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). 4. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells, providing a good segue into discussion of the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html. © 2012 Pearson Education, Inc. 21

4.3 Prokaryotic cells are structurally simpler than eukaryotic cells The DNA of prokaryotic cells is coiled into a region called the nucleoid, but no membrane surrounds the DNA. The surface of prokaryotic cells may be surrounded by a chemically complex cell wall, have a capsule surrounding the cell wall, have short projections that help attach to other cells or the substrate, or have longer projections called flagella that may propel the cell through its liquid environment. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. A visual comparison of prokaryotic and eukaryotic cells, such as that found in Figure 1.3, can be very helpful when discussing the key differences between these cell types. These cells are strikingly different in size and composition. Providing students with a visual reference point rather than simply listing these traits will help them better retain this information. 2. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter of a factor of ten translates into a much greater difference in volume. If students recall enough geometry, you may want to challenge them to calculate the difference in the volume of two cells with diameters that differ by a factor of ten (the answer is about 1,000). 3. 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). 4. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells, providing a good segue into discussion of the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at http://www.pbs.org/wgbh/evolution/educators/lessons/lesson6/act1.html. © 2012 Pearson Education, Inc. 22

A TEM of the bacterium Bacillus coagulans Figure 4.3 Fimbriae Ribosomes Nucleoid Plasma membrane Cell wall Bacterial chromosome Capsule Figure 4.3 A diagram (left) and electron micrograph (right) of a typical prokaryotic cell Flagella A TEM of the bacterium Bacillus coagulans A typical rod-shaped bacterium 23

4.4 Eukaryotic cells are partitioned into functional compartments The structures and organelles of eukaryotic cells perform four basic functions. The nucleus and ribosomes are involved in the genetic control of the cell. The endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes are involved in the manufacture, distribution, and breakdown of molecules. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. © 2012 Pearson Education, Inc. 24

4.4 Eukaryotic cells are partitioned into functional compartments Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing. Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane, and cell wall. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. © 2012 Pearson Education, Inc. 25

4.4 Eukaryotic cells are partitioned into functional compartments The internal membranes of eukaryotic cells partition it into compartments. Cellular metabolism, the many chemical activities of cells, occurs within organelles. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. © 2012 Pearson Education, Inc. 26

4.4 Eukaryotic cells are partitioned into functional compartments Almost all of the organelles and other structures of animals cells are present in plant cells. A few exceptions exist. Lysosomes and centrioles are not found in plant cells. Plant but not animal cells have a rigid cell wall, chloroplasts, and a central vacuole. Student Misconceptions and Concerns Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.22 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.22 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. © 2012 Pearson Education, Inc. 27

Smooth endoplasmic reticulum Rough endoplasmic reticulum NUCLEUS: Figure 4.4A Smooth endoplasmic reticulum Rough endoplasmic reticulum NUCLEUS: Nuclear envelope Chromatin Nucleolus NOT IN MOST PLANT CELLS: Centriole Lysosome Peroxisome Figure 4.4A An animal cell Ribosomes Golgi apparatus CYTOSKELETON: Microtubule Mitochondrion Intermediate filament Microfilament Plasma membrane 28

Rough endoplasmic reticulum NUCLEUS: Nuclear envelope Chromatin Figure 4.4B Rough endoplasmic reticulum NUCLEUS: Nuclear envelope Chromatin Ribosomes Nucleolus Smooth endoplasmic reticulum Golgi apparatus NOT IN ANIMAL CELLS: CYTOSKELETON: Microtubule Central vacuole Intermediate filament Chloroplast Cell wall Microfilament Plasmodesma Figure 4.4B A plant cell Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell 29