Exercises

1.Which of the following are found only in plant cells?

  1. gap junctions
  2. desmosomes
  3. plasmodesmata
  4. tight junctions

2. The principal force driving movement in diffusion is the __________.

  1. temperature
  2. particle size
  3. concentration gradient
  4. membrane surface area

3. What problem is faced by organisms that live in fresh water?

  1. Their bodies tend to take in too much water.
  2. They have no way of controlling their tonicity.
  3. Only salt water poses problems for animals that live in it.
  4. Their bodies tend to lose too much water to their environment.

4. The key components of desmosomes are cadherins and __________.

  1. actin
  2. microfilaments
  3. intermediate filaments
  4. microtubules

5. How does the structure of a plasmodesma differ from that of a gap junction?

6. Explain how the extracellular matrix functions.

7. Discuss why the following affect the rate of diffusion: molecular size, temperature, solution density, and the distance that must be traveled.

8. Why does water move through a membrane?

9. Which plasma membrane component can be either found on its surface or embedded in the membrane structure?

  1. protein
  2. cholesterol
  3. carbohydrate
  4. phospholipid

10. What is the primary function of carbohydrates attached to the exterior of cell membranes?

  1. identification of the cell
  2. flexibility of the membrane
  3. strengthening the membrane
  4. channels through membrane