Chapter 4Cells and Their EnvironmentTRUE/FALSE 1. During diffusion, molecules diffuse from a region where their concentration is low to a region where their concentration is higher, until the particles are evenly dispersed. ANS: F DIF: I OBJ: 4.1.1

2. When the concentration of dissolved particles outside a cell is equal to the concentration of dissolved particles inside the cell, the cell solution is isotonic. ANS: T DIF: I OBJ: 4.1.1

3. Membranes are selectively permeable if they allow only certain substances to move across them. ANS: T DIF: II OBJ: 4.1.1

4. A cell placed in a strong salt solution would probably burst because of osmosis. ANS: F DIF: II OBJ: 4.1.2

5. Water will diffuse out of a cell when the cell is placed in a hypertonic solution. ANS: F DIF: I OBJ: 4.1.2

6. Osmosis is the diffusion of starch molecules through a selectively permeable membrane. ANS: F DIF: I OBJ: 4.1.2

7. The binding of specific molecules to ion channels controls the ability of particular ions to cross the cell membrane. ANS: T DIF: I OBJ: 4.1.3

8. To pass through a cell membrane, water requires carrier proteins. ANS: F DIF: I OBJ: 4.1.4

9. In facilitated diffusion, carrier proteins require energy to transport substances across the cell membrane. ANS: F DIF: I OBJ: 4.1.4

10. The transport of specific particles down their concentration gradient through a membrane by carrier proteins is known as facilitated diffusion. ANS: T DIF: I OBJ: 4.1.4

11. Diffusion is an active process that requires a cell to expend a great deal of energy. ANS: F DIF: I OBJ: 4.1.1

12. Diffusion through ion channels is a form of active transport. ANS: F DIF: I OBJ: 4.2.1

13. Facilitated diffusion moves molecules and ions against their concentration gradient, while active transport moves molecules and ions down their concentration gradient. ANS: F DIF: I OBJ: 4.2.1

14. Passive transport uses ATP to move molecules against their concentration gradient. ANS: F DIF: I OBJ: 4.2.1

15. In active transport, energy is required to move a substance across a cell membrane. ANS: T DIF: I OBJ: 4.2.1

16. The sodium-potassium pump requires energy to move ions across the cell membrane. ANS: T DIF: I OBJ: 4.2.2

17. The sodium-potassium pump moves sodium ions and potassium ions against their concentration gradient. ANS: T DIF: I OBJ: 4.2.2

18. The sodium-potassium pump transports sodium ions out of a cell while causing potassium ions to move into the cell. ANS: T DIF: I OBJ: 4.2.2

19. The sodium-potassium pump uses ATP. ANS: T DIF: I OBJ: 4.2.2

20. Exocytosis is a process that uses vesicles to capture substances and bring them into a cell. ANS: F DIF: I OBJ: 4.2.3

21. Exocytosis helps the cell rid itself of wastes. ANS: T DIF: I OBJ: 4.2.3

22. During the process of exocytosis, the cell membrane extends to engulf substances that are too big to pass through the cell membrane. ANS: F DIF: I OBJ: 4.2.3

23. Exocytosis does not use energy to expel proteins from the cell. ANS: F DIF: I OBJ: 4.2.3

24. Receptor proteins pump sodium ions into a cell. ANS: F DIF: I OBJ: 4.2.4

25. Receptor proteins may cause the formation of a second messenger molecule inside a cell. ANS: T DIF: I OBJ: 4.2.4

26. A receptor protein sends signals into a cell by transporting a specific molecule through the cell membrane. ANS: F DIF: I OBJ: 4.2.4

MULTIPLE CHOICE 1. As a result of diffusion, the concentration of many types of substances a. always remains greater inside a membrane. b. eventually becomes balanced on both sides of a membrane. c. always remains greater outside of a membrane. d. becomes imbalanced on both sides of a membrane. ANS: B DIF: II OBJ: 4.1.1

2. Refer to the illustration above. The process shown is called a. osmosis. c. active transport. b. facilitated diffusion. d. diffusion. ANS: D DIF: II OBJ: 4.1.1

3. Diffusion is the movement of a substance a. only through a lipid bilayer membrane. b. from an area of low concentration to an area of higher concentration. c. only in liquids. d. from an area of high concentration to an area of lower concentration. ANS: D DIF: II OBJ: 4.1.1

4. The dispersal of ink in a beaker of water is an example of a. diffusion. c. active transport. b. osmosis. d. endocytosis. ANS: A DIF: I OBJ: 4.1.1

5. The diffusion of water into or out of a cell is called

a. solubility. b. osmosis. ANS: B 6. Osmosis is a type of a. active transport. b. passive transport. ANS: B DIF: I DIF: I

c. selective transport. d. endocytosis. OBJ: 4.1.2 c. facilitated diffusion. d. endocytosis. OBJ: 4.1.2 c. isotonic solution. d. None of the above OBJ: 4.1.2

7. A cell will swell when it is placed in a(n) a. hypotonic solution. b. hypertonic solution. ANS: A DIF: I

8. The interior portion of a cell membrane forms a nonpolar zone that a. allows polar molecules to pass through the membrane. b. allows food to pass through the membrane. c. prevents ions and most large molecules from passing through the membrane. d. None of the above ANS: C DIF: II OBJ: 4.1.3 c. passive transport. d. active transport. OBJ: 4.1.3

9. Ions move through ion channels by a. endocytosis. b. diffusion. ANS: C DIF: I

10. Ion channel gates close the pores of some ion channels in response to a. stretching of the cell membrane. b. a change in electrical charge. c. the binding of specific molecules to the channel. d. All of the above ANS: D DIF: II OBJ: 4.1.3

11. Proteins that act like selective passageways in the cell membrane are known as a. marker proteins. c. receptor proteins. b. channel proteins. d. None of the above ANS: B DIF: I OBJ: 4.1.3

12. Transport proteins that allow ions to pass through the cell membrane are called a. receptor proteins. c. ion channels. b. marker proteins. d. None of the above ANS: C DIF: I OBJ: 4.1.3 c. osmosis. d. gated channels.

13. Sugar molecules cross the cell membrane by a. active transport. b. facilitated diffusion. ANS: B DIF: I

OBJ: 4.1.4

14. Proteins involved in facilitated diffusion are a. carrier proteins. b. receptor proteins. ANS: A DIF: I

c. Both (a) and (b) d. None of the above OBJ: 4.1.4

15. Sugar molecules can enter cells through the process of a. exocytosis. c. osmosis. b. facilitated diffusion. d. ion pumps. ANS: B DIF: I OBJ: 4.1.4

16. Which of the following does not require energy? a. diffusion c. active transport b. endocytosis d. sodium-potassium pump ANS: A DIF: I OBJ: 4.2.1

17. Unlike passive transport, active transport a. requires energy. b. moves substances down their concentration gradient. c. does not involve carrier proteins. d. All of the above ANS: A DIF: I OBJ: 4.2.1

18. Both active transport and facilitated diffusion involve a. ATP. b. movement against a concentration gradient. c. carrier proteins. d. All of the above ANS: C DIF: I OBJ: 4.2.1

19. Which of the following is a form of active transport? a. osmosis c. facilitated diffusion b. diffusion d. sodium-potassium pump ANS: D DIF: I OBJ: 4.2.1 c. is located in the cytoplasm of a cell. d. transports sugar molecules. OBJ: 4.2.2

20. The sodium-potassium pump a. is a carrier protein b. uses passive transport. ANS: A DIF: I

21. The sodium-potassium pump usually pumps a. potassium ions out of the cell. b. sodium ions into the cell. c. potassium ions into the cell. d. only potassium ions and sugar molecules. ANS: C DIF: II OBJ: 4.2.2

22. The sodium-potassium pump a. increases the concentration of sodium ions inside a cell.

b. decreases the concentration of sodium ions inside a cell. c. increases the concentration of potassium ions inside a cell. d. Both (b) and (c) ANS: D DIF: II OBJ: 4.2.2

23. Proteins and polysaccharides that are too large to move into a cell through diffusion or active transport move in by a. exocytosis. c. the sodium-potassium pump. b. endocytosis. d. None of the above ANS: B DIF: I OBJ: 4.2.3

24. Molecules that are too large to be moved through the membrane can be transported into the cell by a. osmosis. c. exocytosis. b. endocytosis. d. diffusion. ANS: B DIF: I OBJ: 4.2.3

25. Molecules that are too large to be moved across a cell membrane can be removed from the cell by a. diffusion. c. endocytosis. b. exocytosis. d. osmosis. ANS: B DIF: I OBJ: 4.2.3

26. Ridding the cell of materials by discharging the materials in vesicles is called a. osmosis. c. exocytosis. b. diffusion. d. endocytosis. ANS: C DIF: I OBJ: 4.2.3

27. Refer to the illustration above. What happens when the structure labeled A binds to the structure labeled B? a. Information is sent into the cell. c. The cell begins to undergo mitosis. b. Proteins enter the cell. d. None of the above ANS: A DIF: II OBJ: 4.2.4 c. receptor proteins. d. transport proteins. OBJ: 4.2.4

28. Signal molecules bind to a. carbohydrates. b. marker proteins. ANS: C DIF: I

29. When a signal molecule binds to a receptor protein, the receptor protein may

a. b. c. d.

change the permeability of the membrane. cause the formation of a second messenger molecule. catalyze certain chemical reactions in the cell. All of the above DIF: II OBJ: 4.2.4

ANS: D

30. Which of the following transmit information into a cell by binding to signal molecules? a. channel proteins c. marker proteins b. receptor proteins d. end proteins ANS: B COMPLETION 1. The random motion of particles of a substance that causes the substance to move from an area of high concentration to an area of lower concentration is called ____________________. ANS: diffusion DIF: II OBJ: 4.1.1 DIF: I OBJ: 4.2.4

2. The diffusion of ____________________ through cell membranes is called osmosis. ANS: water DIF: I OBJ: 4.1.1

3. Substances always flow from an area of high concentration to an area of ____________________ concentration. ANS: low DIF: I OBJ: 4.1.1

4. When the concentration of free water molecules is higher outside a cell than inside the cell, water will diffuse ____________________ the cell. ANS: into DIF: I OBJ: 4.1.2

5. If a cell is placed in a(n) ____________________ solution, water will flow out of the cell. ANS: hypertonic DIF: I OBJ: 4.1.2

6. If a cell is placed in a(n) ____________________ solution, water will flow into the cell. ANS: hypotonic DIF: I OBJ: 4.1.2

7. If a cell is placed in a(n) ____________________ solution, water flows into the cell at a rate that is equal to the rate at which water flows out of the cell. ANS: isotonic DIF: II OBJ: 4.1.2

8. Diffusion of ions through ion channels is a form of ____________________ transport. ANS: passive DIF: I OBJ: 4.1.3

9. If the interior of a typical cell is negatively charged, ____________________ charged ions will not require energy to diffuse into the cell using an ion channel. ANS: positively DIF: III OBJ: 4.1.3

10. In facilitated diffusion, ____________________ proteins are used to transport substances down their concentration gradient. ANS: carrier DIF: I OBJ: 4.1.4

11. In ____________________ ____________________, carrier proteins do not require energy to transport amino acids into a cell. ANS: facilitated diffusion DIF: II OBJ: 4.1.4

12. Carrier proteins ____________________ shape to transport sugars to the interior of cells. ANS: change DIF: I OBJ: 4.1.4

13. A cell does not expend ____________________ when diffusion takes place. ANS: energy DIF: I OBJ: 4.2.1

14. Active transport requires the use of ____________________ by a cell. ANS: ATP energy DIF: I OBJ: 4.2.1

15. The ____________________-____________________ pump transports ions against their concentration gradients. ANS: sodium potassium DIF: II OBJ: 4.2.2

16. The sodium-potassium pump uses energy supplied by ____________________. ANS: ATP DIF: I OBJ: 4.2.2

17. The sodium-potassium pump prevents the accumulation of ____________________ ions inside the cell. ANS: sodium DIF: I OBJ: 4.2.2

18. The movement of a substance into a cell by a vesicle is called ____________________. ANS: endocytosis DIF: I OBJ: 4.2.3

A

B

19. Refer to the illustration above. The process shown in figure B is called ____________________. ANS: exocytosis DIF: II OBJ: 4.2.3

20. Refer to the illustration above. Cells often engulf extracellular particles and fluid, as shown in figure A. This is called ____________________. ANS: endocytosis DIF: II OBJ: 4.2.3

21. Receptor proteins can change the ____________________ of the cell membrane. ANS: permeability

DIF: I

OBJ: 4.2.4

22. Receptor proteins may act as ____________________, catalyzing certain chemical reactions inside the cell. ANS: enzymes DIF: I OBJ: 4.2.4

23. In the cell membrane, proteins that transmit information into the cell by responding to signal molecules are called ____________________. ANS: receptors DIF: I PROBLEM Paramecia are unicellular protists. They have a number of characteristics also found in animals, such as the need to ingest food in order to obtain energy (they are heterotrophs), and they are surrounded by a cell membrane but not by a rigid cell wall. They have organelles found in animal cells, including a nucleus, mitochondria, ribosomes, and cilia. In addition, they have star-shaped organelles, called contractile vacuoles, that expel excess water. The illustration below depicts a paramecium. OBJ: 4.2.4

1. Refer to the illustration above. The data presented in the table below were obtained in an experiment in which paramecia were placed in different salt concentrations and the rate at which the contractile vacuole contracted to pump out excess water was recorded. Salt Very high High Medium Low Very low Rate of contractile vacuole contractions/minute 2 8 15 22 30

a. How can you explain the observed relationship between salt concentration and rate of contractile vacuole contraction?

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? Why? ANS: a. The contractile vacuole maintains water balance by pumping water out of the cell. When the salt concentration outside of the cell is very high, water will move from inside the cell to outside the cell-little or no pumping action is required. When the salt concentration outside of the cell is low, the tendency is for water to move from outside the cell to inside the cell, necessitating increased pumping action by the vacuole to move excess water out of the cell. b. If the contractile vacuole were to stop contracting, the cell would burst because water would collect in excess inside of it and the cell membrane would not be strong enough to resist rupturing. This result would be expected to occur more quickly if the organism were placed in water with a low salt concentration than it would if the organism were placed in water with a high salt concentration. This is because water accumulates inside the paramecium more rapidly when it is placed in a low salt environment. DIF: III OBJ: 4.1.2

2. 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: 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 across cell membranes by facilitated diffusion. Do you agree with his conclusion? Why or why not? ANS: Students should disagree. The information that cells can accumulate the molecule against a concentration gradient is compelling evidence that active transport is the mechanism of transport. Active transport also requires energy consumption, which was also found to be a property of transport of this molecule. DIF: III ESSAY 1. Why do dissolved particles on one side of a membrane result in the diffusion of water across the membrane? ANS: Dissolved particles reduce the number of water molecules that can move freely on that side. Water then moves by osmosis from the side where the free water molecule concentration is high to the side where the concentration is lower. DIF: III OBJ: 4.1.2 OBJ: 4.2.1

2. Why is it dangerous for humans to drink sea water?

ANS: The concentration of salt in sea water is higher than the concentration of salt in the fluids that surround the cells in the human body. Drinking sea water increases the concentration of salt in the bodys fluids. This causes water to leave the cells by osmosis, and without the proper amount of water, the cells will be harmed or will die. DIF: III OBJ: 4.1.2

3. Distinguish between facilitated diffusion and active transport. ANS: In facilitated diffusion, carrier proteins assist the diffusion of substances down their concentration gradient. Active transport, on the other hand, is the movement of substances against their concentration gradient. DIF: III OBJ: 4.2.1

A

B

4. Refer to the illustration above. Identify and explain the processes taking place in figure A and figure B. ANS: Endocytosis is the process taking place in figure A. Endocytosis is the process by which cells engulf substances that are too large to enter the cell, by enclosing the substances in vesicles. Exocytosis is the process taking place in figure B. Exocytosis is the process by which cells export substances and discharge waste from vesicles at the cells surface. DIF: III OBJ: 4.2.3

5. Describe three ways in which the binding of a signal molecule to a receptor protein can change the functioning of a cell. ANS: 1. The receptor can act as an enzyme. 2. The receptor may cause the formation of a second messenger that will have an effect in another part of the cytoplasm. 3. The receptor can cause membrane channels to open. DIF: III OBJ: 4.2.4