1. Unit Three: Short Answer Questions
Cellular Transport
Unit Three: Short Answer Questions

2. --Beaker A contains 0.8 percent NaCl.
The cell membrane of red blood cells is permeable to water but not to sodium chloride, NaCl. Suppose that you have three beakers:
--Beaker A contains 0.8 percent NaCl.
--Beaker B contains 1.3 percent NaCl
--Beaker C contains 0.2 percent NaCl
To each beaker, you add red blood cells, which contain a solution that is 0.8 percent NaCl.
Predict what will happen to the red blood cells in Beaker A and explain why using your science vocabulary.
 The cell will remain the same size because it is in an isotonic solution and water will be moving into and out of the cell at an even rate.
Predict what will happen to the red blood cells in Beaker B and explain why using your science vocabulary.
 The cell will shrink because it was placed in a hypertonic solution and the water will water out of the cell to follow the high concentration of solute in the beaker.
Predict what will happen to the red blood cells in Beaker C and explain why using your science vocabulary.
The cell will swell because it was placed in a hypotonic solution and the water will move into the cell to follow the high concentration of solute in the cell.

3. 2. A selectively permeable membrane separates the solutions in the arms of the U-tube shown below. The membrane is permeable to water and Substance B but not to substance A. Twenty grams of substance A and forty grams of substance B have been added to the water on side 1 of the U-tube. Forty grams of substance A and ten grams of substance B have been added to the water on side 2 of the U-tube. Assume that after a period of time, the solutions on either side of the membrane have reached equilibrium. Use this information to help you answer the questions below.
How many grams of substance A will be in solution on side 1 of the U-tube? How many grams of substance A will be on side 2 of the U-tube. Explain your answer.
How many grams of substance B will be in solution on side 1 of the U-tube? How many grams of substance B will be on side 2 of the U-tube? Explain your answer.
c. What has happened to the water level in the U-tube? Explain your answer.

4. 3. A biologist conducts an experiment designed to determine whether a particular type of molecule is transported into cells by diffusion, facilitated diffusion, or active transport. He collects the following information during his study:
1. The molecule is very small.
2. The molecule is polar.
3. The molecule can accumulate inside a cell, even when its concentration inside the cell initially
is higher than it is outside the cell.
4. Cells use up more energy when the molecule is present in the environment around the cells than when it is not present.
The biologist concludes that the molecule moves cross the cell membrane by facilitated diffusion. Do you agree with his conclusion? Use the above information to explain your reasons for agreeing or disagreeing.

5. The biologist concludes that the molecule moves cross the cell membrane by facilitated diffusion. Do you agree with his conclusion? Use the above information to explain your reasons for agreeing or disagreeing.
I do not agree with the biologist that his evidence supports the molecules movement by facilitated diffusion. His first two points that the molecules is small and moves through a protein do support facilitated diffusion. However, only active transport moves from low to high and requires energy. Based on the evidence, I believe that the molecule was moving via active transport.

6. The data presented in the table below were obtained in an experiment in which paramecium were placed in different salt concentrations and the rate at which the contractile vacuole contracted to pump out excess water was recorded.
How can you explain the observed relationship between salt concentration and rate of contractile vacuole contractions in terms of what you know about osmotic solutions?
The lower the salt content the greater the number of contractions and the high the salt content the fewer the number of contractions. When placed in a hypotonic solution the contractile vacuole contracted more versus a hypertonic environment the contractile vacuole contracted less.

7. b. If something happened to a paramecium that caused its contractile vacuole to stop contracting, what would you expect to happen? Would this result occur more quickly if the paramecium was in water with a high salt concentration or in water with a low salt concentration? Explain your answer in terms of what you know about osmosis and solutions. If the paramecium was unable to contract its vacuole, it would fill up with water and be in danger of bursting. This would occur faster in a hypotonic environment because it is normally found in a hypertonic environment with less water and more solute.

8. 5. Please list and briefly describe the three types of proteins found in the membrane. Be sure you explain their functions thoroughly and give an example of each. a) Transport proteins: allow molecules to pass through a polar portion of the cell membrane. b) Receptor proteins: transfer information from one side to the other. c) Marker proteins: act as identification for the cell. (Example: Blood types).

9. 6. List three comparisons and three differences between osmosis and diffusion. Osmosis Movement of water Across a semi-permeable membrane Channel protein required to pass nonpolar region Diffusion No semi-permeable membrane required Movement of small particles Without the assistance of a channel protein Both High to Low Passive Transport Solutes move until they find equilibrium

10. 7. What is the major limitation that cells face
7. What is the major limitation that cells face? Discuss how volume versus surface area impacts a cell’s ability to function efficiently in an organism. Cells can’t be too small because they must fit all of their organelles. Cells can’t be too big because the needed to move food and wastes into and out of the cell efficiently. High surface area to volume ratio. More surfaces transport items into and out of the cell.

11. 8. What are the effects of cells when they are placed in a hypotonic solution, hypertonic solution, and isotonic solution? If a cell is placed in a hypotonic solution, it will swell. If a cell is placed in a hypertonic solution, it will shrink. If a cell is placed in an isotonic solution, it will not change shape.

12. 9. Can humans drink salt water for hydration. Why or why not
9.Can humans drink salt water for hydration? Why or why not? Humans cannot drink salt water for hydration because salt water is hypertonic to human cells and will cause their cells to shrink.

13. 10. List and describe the role of the three two molecules that cell membranes are composed of. The two molecules that the cell membrane is composed of are phospholipids and proteins. The phospholipids act as a nonpolar wall that can provide a fluid structure to the cell without dissolving in water. The proteins act as a method of transport for nonpolar molecules, receptor for cell communication, and marker for cell identification.

14. 11. How are molecules moved that are too big to fit through membrane proteins? How are molecules moved into and out of the cell? Describe both processes in terms of a cell membrane. Molecules that are too big to pass through the membrane proteins are moved into and out of the cell by active transport. Endocytosis is utilized to move food and/ or water into the cell. The item collects near the cell membrane and a vesicle begins to form to transport the item. The vesicle will pinch off and float into the cell. Exocytosis occurs when waste collects inside the cell membrane and a vesicle forms. This takes place in the opposite direction of endocytosis, budding off and moving out of the cell.

15. 12. Why would water molecules need a transport protein to move rapidly and in large quantities across a membrane? Water molecules are polar and need a transport protein to travel through the nonpolar center of the cell membrane.

16. 13. In the supermarket, produce is often sprayed with water
13. In the supermarket, produce is often sprayed with water. Explain why this makes vegetables look crisp. The water is hypotonic to the produce and thus moves into the plant cells causing them to swell. This creates the impression of crispness.