1. Chapter 4 A Tour of the Cell
Chapter 4 A Tour of the Cell

2. Introduction: Cells on the Move
Cells, the simplest collection of matter that can live, were first observed by Robert Hooke in 1665
Antoni van Leeuwenhoek later described cells that could move – bacteria
Although cell movement attracted the early scientists, we know today that not all cells move
The early microscopes provided data to establish the cell theory
That is, all living things are composed of cells and that all cells come from other cells
Leeuwenhoek was a haberdasher who developed the microscope to magnify the cloth he used to make clothing. His greatest contribution to science was his curiosity. As a result, he observed “animalcules” in a variety of liquids and reported his findings to the most prestigious science society of the day, the Royal Society of London.
Copyright © 2009 Pearson Education, Inc.

3. 4.1 Microscopes reveal the world of the cell
Describe microscopes and their importance in viewing cellular structure
The most frequently used microscope is the light microscope (LM)—like the one used in biology laboratories- to 1000X (400X)
Biologists often use a very powerful microscope called the electron microscope (EM) to view the ultrastructure of cells -100,000 X
With today’s modern light microscopes, images can be directed onto photographic film or a digital sensor, or onto a video screen.
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.
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 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 same way a compound light microscope or TEM works!
Copyright © 2009 Pearson Education, Inc.

4. Eyepiece Enlarges image formed by objective lens Ocular lens
Magnifies specimen,
forming primary
image
Objective lens
Specimen
Condenser
lens
Focuses light
through specimen
Figure 4.1A Light microscope (LM)
Light
source

5. What a plant cell looks like with a light microscope

6. 4.2 Most cells are microscopic
Most cells cannot be seen without a microscope
Cell size is variable
The surface area of a cell is important for carrying out the cell’s functions, such as acquiring adequate nutrients and oxygen
A small cell has more surface area relative to its cell volume and is more efficient
Because it is difficult to study the functions of cell components in intact cells, scientists have developed techniques to isolate specific cell components for study of functions.
For BLAST Animation Eukaryotic Cell Shape and Surface Area, go to Animation and Video Files.
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 is 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.
Copyright © 2009 Pearson Education, Inc.

7. 4.3 Prokaryotic cells are structurally simpler than eukaryotic cells
Distinguish between prokaryotic and eukaryotic cells
Bacteria and archaea are prokaryotic cells
All other forms of life are eukaryotic cells
Both prokaryotic and eukaryotic cells have a plasma membrane and one or more chromosomes and ribosomes
Eukaryotic cells have a membrane-bound nucleus and a number of other organelles, whereas prokaryotes have a nucleoid and no true organelles
Bacteria have a single chromosome that is found within the cell in the form of a circle (no free ends). They have extrachromosomal DNA called plasmids, but they are not necessary for viability of the cell.
Students should be reminded that there are possible evolutionary relationships between prokaryotic and eukaryotic cells and questioned about these relationships. Did eukaryotic cells evolve from bacteria-like organisms or perhaps Archaea?
For the BLAST Animation Prokaryotic Cell Size, go to Animation and Video Files.
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. A visual comparison of prokaryotic and eukaryotic cells, such as that found in Figure 1.4, 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.
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
Copyright © 2009 Pearson Education, Inc.

8. 10 m 1 m 100 mm Unaided eye (10 cm) 10 mm (1 cm) 1 mm 100 µm
Human height
1 m
Length of some
nerve and
muscle cells
100 mm
(10 cm)
Unaided eye
Chicken egg
10 mm
(1 cm)
Frog egg
1 mm
100 µm
Most plant
and animal
cells
Light microscope
10 µm
Nucleus
Most bacteria
Mitochondrion
1 µm
Figure 4.2A The sizes of cells and related objects.
Mycoplasmas
(smallest bacteria)
Electron microscope
100 nm
Viruses
Ribosome
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms

9. Generalized prokaryotic cell
Pili
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
Figure 4.3 A structural diagram of a typical prokaryotic cell.
Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at
Flagella
Generalized prokaryotic cell

10. 4.4 Eukaryotic cells are partitioned into functional compartments
There are four life processes in eukaryotic cells that depend upon structures and organelles
Manufacturing
Breakdown of molecules
Energy processing
Structural support, movement, and communication
Teaching Tips
1. 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.
Copyright © 2009 Pearson Education, Inc.

11. Generalized animal cell
NUCLEUS:
Generalized animal cell
Nuclear envelope
Chromosomes
Smooth endoplasmic
reticulum
Nucleolus
Rough
endoplasmic
reticulum
Lysosome
Centriole
Ribosomes
Figure 4.4A An animal cell.
Peroxisome
Golgi
apparatus
CYTOSKELETON:
Microtubule
Plasma membrane
Intermediate
filament
Mitochondrion
Microfilament

12. Generalized plant cell
NUCLEUS:
Rough endoplasmic
reticulum
Nuclear envelope
Chromosome
Ribosomes
Nucleolus
Smooth
endoplasmic
reticulum
Golgi
apparatus
CYTOSKELETON:
Central vacuole
Microtubule
Chloroplast
Intermediate
filament
Cell wall
Plasmodesmata
Microfilament
Figure 4.4B A plant cell.
Mitochondrion
Peroxisome
Plasma membrane
Generalized plant cell
Cell wall of
adjacent cell

13. 4.5 The structure of membranes correlates with their functions
Describe the structure of cell membranes and how membrane structure relates to function
The plasma membrane controls the movement of molecules into and out of the cell, a trait called selective permeability
The structure of the membrane with its component molecules is responsible for this characteristic
Membranes are made of lipids, proteins, and some carbohydrate, but the most abundant lipids are phospholipids
The plasma membrane provides a good example of the link between the structure of an organelle and its function.
One of the earliest episodes in the evolution of life may have been the formation of a membrane.
Teaching Tips
1. 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 selfhealing. That the properties of phospholipids emerge from their organization is worth emphasizing to students.
2. 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.)
Copyright © 2009 Pearson Education, Inc.

14. 4.5 The structure of membranes correlates with their functions
Phospholipids form a two-layer sheet called a phospholipid bilayer
Hydrophilic heads face outward, and hydrophobic tails point inward
Thus, hydrophilic heads are exposed to water, while hydrophobic tails are shielded from water
Proteins are attached to the surface, and some are embedded into the phospholipid bilayer
A major function of the phospholipid bilayer is selective permeability. However, because of their composition, some molecules can simply diffuse across, whereas others need help.
The hydrophobic and hydrophilic ends of a phospholipid molecule naturally 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). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing.
Teaching Tips
1. 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 selfhealing. That the properties of phospholipids emerge from their organization is worth emphasizing to students.
2. 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.)
Copyright © 2009 Pearson Education, Inc.

15. The cell membrane is a lipid bilayer with embedded proteins
Outside cell
Hydrophilic
heads
Hydrophobic
region of
protein
Hydrophobic
tails
Inside cell
Proteins
Figure 4.5B Phospholipid bilayer with associated proteins.
Hydrophilic
region of
protein

16. Cell structures involved in manufacturing and breakdown
Nucleus
Ribosomes
Endomembrane system
Discuss ways that cellular organelles are involved in the manufacture and breakdown of important cellular molecules

17. 4.6 The nucleus is the cell’s genetic control center
The nucleus controls the cell’s activities and is responsible for inheritance
Inside is a complex of proteins and DNA called chromatin, which makes up the cell’s chromosomes
DNA is copied within the nucleus prior to cell division
The DNA within the nucleus contains genetic information that must be faithfully replicated and partitioned between two daughter cells to maintain the species.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell.
2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office.
3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals.
4. 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 like making a working photocopy of an important document, keeping the original copy safely stored away.
Copyright © 2009 Pearson Education, Inc.

18. 4.7 Ribosomes make proteins for use in the cell and export
Ribosomes are involved in the cell’s protein synthesis
Ribosomes are synthesized in the nucleolus, which is found in the nucleus
Cells that must synthesize large amounts of protein have a large number of ribosomes
Some ribosomes are free ribosomes; others are bound
Free ribosomes are suspended in the cytoplasm
Bound ribosomes are attached to the endoplasmic reticulum (ER) associated with the nuclear envelope
An example of a cell that at times must make a large amount of protein is a lymphocyte, a white blood cell. Upon stimulation by infectious agents like bacteria, it pumps out a significant amount of antibody, a protein, to fight the infection.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. 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.)
Copyright © 2009 Pearson Education, Inc.

19. Endoplasmic reticulum (ER)
Ribosomes
Cytoplasm ER
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
Figure 4.7 Ribosomes.
Small
subunit
TEM showing ER
and ribosomes
Diagram of
a ribosome

20. 4.8 Overview: Many cell organelles are connected through the endomembrane system
The membranes within a eukaryotic cell are physically connected and compose the endomembrane system
The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane
Some components of the endomembrane system are able to communicate with others with formation and transfer of small membrane segments called vesicles
One important result of communication is the synthesis, storage, and export of molecules
In general, the endomembrane system regulates protein traffic and performs metabolic functions in the cell.
It accounts for more than half the total membrane in many eukaryotic cells.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Point out to your students that the endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus.
Copyright © 2009 Pearson Education, Inc.

21. 4.9 The endoplasmic reticulum is a biosynthetic factory
Smooth ER is involved in a variety of diverse metabolic processes
For example, enzymes produced by the smooth ER are involved in the synthesis of lipids, oils, phospholipids, and steroids
Rough ER makes additional membrane for itself and proteins destined for secretion
Once proteins are synthesized, they are transported in vesicles to other parts of the endomembrane system
Smooth ER processes include synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory.
Copyright © 2009 Pearson Education, Inc.

22. Nuclear envelope Ribosomes Smooth ER Rough ER
Figure 4.9A Smooth and rough endoplasmic reticulum.

23. 4.10 The Golgi apparatus finishes, sorts, and ships cell products
The Golgi apparatus functions in conjunction with the ER by modifying products of the ER
Products travel in transport vesicles from the ER to the Golgi apparatus
One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock
Products are modified as they go from one side of the Golgi apparatus to the other and travel in vesicles to other sites
The finished product can become part of the plasma membrane or other organelle, or it may move to the plasma membrane for export from the cell.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Some people think the Golgi apparatus looks like a stack of pita bread.
2. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory.
Copyright © 2009 Pearson Education, Inc.

24. Golgi apparatus “Receiving” side of Golgi Golgi apparatus apparatus
Transport
vesicle
from ER
New vesicle
forming
Figure 4.10 The Golgi apparatus.
You might tell your students that the Golgi apparatus looks like a stack of pita bread.
Transport
vesicle from
the Golgi
“Shipping” side
of Golgi apparatus

25. 4.11 Lysosomes are digestive compartments within a cell
A lysosome is a membranous sac containing digestive enzymes
The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing
The membrane serves to safely isolate these potent enzymes from the rest of the cell
One of the several functions of lysosomes is to remove or recycle damaged parts of a cell
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. As noted in Module 4.11, lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.”
Copyright © 2009 Pearson Education, Inc.

26. Lysosome fusing with a food vacuole to digest food-dude
Digestive
enzymes
Lysosome
Plasma
membrane
Digestion
Food vacuole
Figure 4.11A Lysosome fusing with a food vacuole and digesting food.

27. Lysosome breaking down and recycling a mitochondrion
Digestion
Figure 4.11B Lysosome fusing with vesicle containing damaged organelle and digesting and recycling its contents.
Vesicle containing
damaged mitochondrion

28. 4.12 Vacuoles function in the general maintenance of the cell
Vacuoles are membranous sacs that are found in a variety of cells and possess an assortment of functions
Examples are the central vacuole in plants with hydrolytic functions, pigment vacuoles in plants to provide color to flowers, and contractile vacuoles in some protists to expel water from the cell
For the BLAST Animation Vacuoles, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Challenge your students to identify animal cell organelles other than mitochondria that are not involved in the synthesis of proteins. (Vacuoles and peroxisomes are not involved in protein synthesis).
Video: Paramecium Vacuole
Copyright © 2009 Pearson Education, Inc.

29. Cell structures involved in energy conversion
Mitochondria
Chloroplast
Describe the function of each cellular organelle that is involved in energy conversion

30. 4.14 Mitochondria harvest chemical energy from food
Cellular respiration is accomplished in the mitochondria of eukaryotic cells
Cellular respiration involves conversion of chemical energy in foods to chemical energy = ATP (adenosine triphosphate)
Mitochondria have two internal compartments
The intermembrane space, which encloses the mitochondrial matrix where materials necessary for ATP generation are found
A cell may have thousands of mitochondria.
For the BLAST Animation Mitochondria, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night.
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.
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31. Mitochondrion Outer membrane Intermembrane space Inner membrane
Figure 4.14 The mitochondrion.
Inner
membrane
Cristae
Matrix

32. 4.15 Chloroplasts convert solar energy to chemical energy
Chloroplasts are the photosynthesizing organelles of plants
Photosynthesis is the conversion of light energy to chemical energy of sugar molecules
Chloroplasts are partitioned into compartments
The important parts of chloroplasts are the stroma, thylakoids, and grana
Chloroplasts contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar.
Student Misconceptions and Concerns
1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night.
Teaching Tips
1. 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.
Copyright © 2009 Pearson Education, Inc.

33. Chloroplast Stroma Inner and outer membranes Granum Intermembrane
Figure 4.15 The chloroplast.
Granum
Intermembrane
space

34. Cell structures involved in internal and external support
Cytoskeleton
Cilia/flagella
Extracellular matrix
Cell junctions
Cell wall
Describe the function of each cellular organelle that is involved in internal and external support of the cell

35. Video: Cytoplasmic Streaming
4.17 The cell’s internal skeleton helps organize its structure and activities
Cells contain a network of protein fibers, called the cytoskeleton, that functions in cell structural support and motility
Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins
Motor proteins work with cytoskeletal elements and the plasma membrane to help cells move. Also, vesicles and other organelles travel to their destinations along the cytoskeletal “monorail.”
Student Misconceptions and Concerns
1. Students often regard the cytosol as little more than a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. Module 4.17 describes the dynamic and diverse functions of the cytoskeleton.
Teaching Tips
1. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have a structural framework that is routinely constructed, deconstructed, and then reconstructed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reconstructed repeatedly, but typically rely upon the same basic design.) Thus, caution is especially warranted when using such analogies.
Video: Cytoplasmic Streaming
Copyright © 2009 Pearson Education, Inc.

36. Receptor for motor protein
Vesicle
ATP
Receptor for motor protein
Motor protein (ATP powered)
Microtubule
of cytoskeleton
(a)
Microtubule
Vesicles
0.25 µm
Campbell, Neil, and Jane Reece, Biology, 8th ed., Figure 6.21 Motor proteins and the cytoskeleton. (a) Motor proteins that attach to receptors on vesicles can “walk” the vesicles along microtubules or, in some cases, microfilaments; Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a).
(b)

37. The cytoskeleton is composed of three kinds of fibers
4.17 The cell’s internal skeleton helps organize its structure and activities
The cytoskeleton is composed of three kinds of fibers
Microfilaments (actin filaments) support the cell’s shape and are involved in motility
Intermediate filaments reinforce cell shape and anchor organelles
Microtubules (made of tubulin) shape the cell and act as tracks for motor protein
A specialized arrangement of microtubules in eukaryotes is responsible for the beating of flagella (human sperm) and cilia (cells of the human respiratory tract).
Student Misconceptions and Concerns
1. Students often regard the cytosol as little more than a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. Module 4.17 describes the dynamic and diverse functions of the cytoskeleton.
Teaching Tips
1. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have a structural framework that is routinely constructed, deconstructed, and then reconstructed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reconstructed repeatedly, but typically rely upon the same basic design.) Thus, caution is especially warranted when using such analogies
Copyright © 2009 Pearson Education, Inc.

38. Intermediate filament Microtubule
Nucleus
Nucleus
Actin subunit
Fibrous subunits
Tubulin subunit
Figure 4.17 Fibers of the cytoskeleton: microfilaments are stained red (left), intermediate filaments are stained yellow-green (center), and microtubules are stained green (right).
7 nm
10 nm
25 nm
Microfilament
Intermediate filament
Microtubule

39. 4.18 Cilia and flagella move when microtubules bend
While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons
Cells that sweep mucus out of our lungs have cilia
Animal sperm are flagellated
Student Misconceptions and Concerns
1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed.
Teaching Tips
1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach!
Video: Paramecium Cilia
Video: Chlamydomonas
Copyright © 2009 Pearson Education, Inc.

40. 4.18 Cilia and flagella move when microtubules bend
Both flagella and cilia are made of microtubules wrapped in an extension of the plasma membrane
A ring of nine microtubule doublets surrounds a central pair of microtubules
This arrangement is called the pattern and is anchored in a basal body with nine microtubule triplets arranged in a ring
Student Misconceptions and Concerns
1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed.
Teaching Tips
1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach!
Animation: Cilia and Flagella
Copyright © 2009 Pearson Education, Inc.

41. Cross sections: Outer microtubule doublet Central microtubules
Radial spoke
Dynein arms
Flagellum
Plasma
membrane
Figure 4.18C Structure of a eukaryotic flagellum or cilium.
Triplet
Basal body
Basal body

42. There has been a decline in sperm quality
4.19 CONNECTION: Problems with sperm motility may be environmental or genetic
There has been a decline in sperm quality
A group of chemicals called phthalates used in a variety of things people use every day may be the cause
On the other hand, there are genetic reasons that sperm lack motility
Primary ciliary dyskinesia (PCD) is an example
PCD is a rare disease in which there is an absence of dynein arms, which prevents microtubules from bending.
Teaching Tips
1. Primary ciliary dyskinesia results in nonmotile cilia. Module 4.19 describes infertility in males due to immotile sperm. Challenge your students to suggest reasons why this same disease might reduce fertility in an affected woman. (In the oviduct, cilia convey the egg along the oviduct toward the uterus.)
Copyright © 2009 Pearson Education, Inc.

43. 4.20 The extracellular matrix of animal cells functions in support, movement, and regulation
Cells synthesize and secrete the extracellular matrix (ECM) that is essential to cell function
The ECM is composed of strong fibers of collagen, which holds cells together and protects the plasma membrane
ECM attaches through connecting proteins that bind to membrane proteins called integrins
Integrins span the plasma membrane and connect to microfilaments of the cytoskeleton
Integrins have the function of “integrating” information from outside to inside the cell and, thus, essentially regulate a cell’s behavior.
Student Misconceptions and Concerns
1. The structure and functions of the extracellular matrix (ECM) are closely associated with the cells that it contacts. Students might suspect that like roots from a tree, cells are anchored to the matrix indefinitely. However, some cells can detach from the ECM and migrate great distances, often following molecular trails (such as fibronectin and laminin) that direct them along the journey.
Teaching Tips
1. The extracellular matrix forms a significant structural component of many connective tissues, including cartilage and bone. Many of the properties of cartilage and bone are directly related to the large quantities of material sandwiched between the bone (osteocyte) and cartilage (chondrocyte) cells.
Copyright © 2009 Pearson Education, Inc.

44. EXTRACELLULAR FLUID CYTOPLASM Glycoprotein complex with long
polysaccharide
EXTRACELLULAR FLUID
Collagen fiber
Connecting
glycoprotein
Integrin
Plasma
membrane
Figure 4.20 The extracellular matrix (ECM) of an animal cell.
Microfilaments
CYTOPLASM

45. 4.21 Three types of cell junctions are found in animal tissues
Adjacent cells communicate, interact, and adhere through specialized junctions between them
Tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells
Anchoring junctions fasten cells together into sheets
Gap junctions are channels that allow molecules to flow between cells
Teaching Tips
1. Tight junctions form a seal that prevents the movement of fluids past the region of the junction. Functionally, this is similar to the lengthy zipper-like seal at the top of plastic food storage bags.
Animation: Desmosomes
Animation: Gap Junctions
Animation: Tight Junctions
Copyright © 2009 Pearson Education, Inc.

46. Tight junctions Anchoring junction Gap junctions Plasma membranes
Figure 4.21 Three types of cell junctions in animal tissues.
Plasma membranes
of adjacent cells
Extracellular matrix

47. 4.22 Cell walls enclose and support plant cells
Plant, but not animal cells, have a rigid cell wall
It protects and provides skeletal support that helps keep the plant upright against gravity
Plant cell walls are composed primarily of cellulose
Plant cells have cell junctions called plasmodesmata that serve in communication between cells
For the BLAST Animation Signaling: Direct, go to Animation and Video Files.
For the BLAST Animation Plant Cell Wall, go to Animation and Video Files.
Teaching Tips
1. Consider challenging your students to suggest analogies to the structure and function of plasmodesmata. Critically examining the similarities and differences of their suggestions requires a careful understanding of structure and function.
2. The text in Module 4.22 compares the fibers-in-a-matrix construction of a plant cell wall to fiberglass. Students familiar with highway construction or the pouring of concrete might also be familiar with the frequent use of reinforcing bar (rebar) to similarly reinforce concrete.
Copyright © 2009 Pearson Education, Inc.

48. Walls of two adjacent plant cells Vacuole Plasmodesmata
Primary cell wall
Figure 4.22 Plant cell walls and cell junction.
Secondary cell wall
Cytoplasm
Plasma membrane

49. 4.23 Review: Eukaryotic cell structures can be grouped on the basis of four basic functions
It is possible to group cell organelles into four categories based on general functions of organelles
In each category structure is correlated with function
Student Misconceptions and Concerns
1. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.23 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 4.23 and referring to it regularly as the chapter is studied and/or discussed.
Teaching Tips
1. The chapter ends by noting the three fundamental features of all organisms. Challenge students to explain if viruses are organisms according to this definition.
2. Some students might benefit by creating a concept map integrating the information in Table Such a map would note the components of a cell interconnected by lines and relationships between these cellular components. Such techniques may also be beneficial in later chapters, depending upon the learning style of particular students.
Copyright © 2009 Pearson Education, Inc.

50. Table 4.23 Eukaryotic Cell Structures and Functions.

51. Resources for chapter 4
Using your disc that came with your text, go to Student Home, Chapter 4: A tour of the cell.
Take the pre test
Complete activities.
Test yourself
Extend your knowledge
Biofix – Tour of plant cell and tour of animal cell.
Current events –NY Times article, Antennae on cell surface if the key to development and disease, answer the five questions and to me.
We will be having a short answer quiz on this chapter.