Concepts of Cellular Structure

Objectives

When you have completed this section, you should be able to

• discuss the development and modern tenets of the cell theory;
• describe the shapes and sizes of cells and their components; and
• explain how early concepts of cellular structure were revised with the advent of new technology.

Think About It

Can you conceive of some other reasons for an organ to consist of many small cells rather than fewer, larger ones?

Key Point Review

1. When was the idea of spontaneous generation of cells laid to rest? Who were some people who questioned the idea?

2. What are the tenets of the cell theory?

3. Define cytoplasm, cytosol, and organelle.

4. What is the main advantage of an electron microscope over a light microscope?

The Cell Surface

Objectives

When you have completed this section, you should be able to

• describe the structure of unit membranes, especially the plasma membrane;
• explain the functions of the protein, lipid, and carbohydrate components of the cell surface; and
• describe the structure and function of microvilli, cilia, and flagella.

Think About It

What would happen if a plasma membrane were made primarily of a hydrophilic substance such as carbohydrate? Which of the major themes at the end of chapter 1 does this exemplify?

Think About It

How would it affect mucus of the respiratory tract if cilia were equally stiff on both the power and recovery strokes?

Key Point Review

5. How does the structure of a plasma membrane depend on the amphiphilic nature of phospholipids?

6. Distinguish between integral and peripheral proteins.

7. Why is the glycocalyx important to survival?

8. How do microvilli and cilia differ in structure and function? What is one role that both of them sometimes play?

The Cell Interior

Objectives

When you have completed this section, you should be able to

• list the main organelles of a cell and state their functions;
• describe the cytoskeleton and its functions; and
• explain how cell inclusions differ from organelles and give some examples of inclusions.

Key Point Review

9. Distinguish between organelles and inclusions. Give two examples of each.

10. Briefly state how each of the following cell components can be microscopically recognized: nucleus, mitochondrion, lysosome, and centriole. What is the primary function of each?

11. Which three organelles are involved in protein synthesis?

12. In what ways do rough and smooth endoplasmic reticulum differ?

13. Define centriole, microtubule, cytoskeleton, and axoneme. How do these structures relate to each other?

Membrane Transport-Passive Mechanisms

Objectives

When you have completed this section, you should be able to

• distinguish between passive and active mechanisms of membrane transport;
• describe the passive mechanisms for moving substances through plasma membranes;
• explain how an equilibrium can arise that balances osmosis and filtration;
• explain the concepts of osmotic pressure and tonicity; and
• compare the characteristics of carrier-mediated transport with enzyme function.

Think About It

Would the fluid level on side A rise, fall, or remain the same if the concentration of albumin on side A were reduced? Why?

Key Point Review

14. How is filtration relevant to human physiology?

15. How does osmosis help maintain blood volume?

16. Why is it important that saline solutions given intravenously to a patient be isotonic?

17. How is net diffusion different from simple diffusion? In what ways are they similar?

Membrane Transport-Active Mechanisms

Objectives

When you have completed this section, you should be able to

• define active transport and explain how this process works;
• distinguish between symport and antiport systems;
• describe the functions of the sodium-potassium pump; and
• describe the different types of bulk transport.

Key Point Review

18. How is active transport similar to facilitated diffusion? How is it different?

19. How does the Na⁺-K⁺ pump exchange sodium ions for potassium ions across the plasma membrane? What is the pump used for?

20. How does phagocytosis differ from pinocytosis?

21. Distinguish between the two kinds of pinocytosis.

22. Describe the process of exocytosis. What are some of the purposes it serves?

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