1. Animal Nutrition

2. Essential amino acids are
all of the amino acids required to make proteins.
those that cannot be made in the body.
those that contain nitrogen.
obtained only by eating plants.
obtained only by eating animals.
Answer: b
This question relates to Concept Essential nutrients are those that cannot be synthesized.

3. Essential amino acids are
all of the amino acids required to make proteins.
those that cannot be made in the body.
those that contain nitrogen.
obtained only by eating plants.
obtained only by eating animals. 3

4. A “complete digestive tract” differs from a gastrovascular cavity in that only the complete tract
permits extracellular digestion.
has teeth and tentacles to help with ingestion.
uses its surface area for nutrient absorption.
has specialized compartments.
allows elimination of undigested wastes.
Answer: d
This question relates to Concept 41. Options A, B, C, and E are true for both the gastrovascular cavity and complete gut. 4

5. A “complete digestive tract” differs from a gastrovascular cavity in that only the complete tract
permits extracellular digestion.
has teeth and tentacles to help with ingestion.
uses its surface area for nutrient absorption.
has specialized compartments.
allows elimination of undigested wastes. 5

6. In humans, the first opportunity for ingested food to undergo enzymatic hydrolysis is in the
mouth.
stomach.
liver.
small intestine.
large intestine.
Answer: a
This question relates to Concept Salivary amylase digests starch macromolecules into smaller molecules. 6

7. In humans, the first opportunity for ingested food to undergo enzymatic hydrolysis is in the
mouth.
stomach.
liver.
small intestine.
large intestine. 7

8. Stomach acid splits polypeptides into amino acids.
splits fats into fatty acids and glycerol.
activates pepsinogen into pepsin.
initiates the development of stomach ulcers.
inhibits the production of epithelial cells.
Answer: c
This question relates to Concept Options A and B are controlled by enzymes, not HCl; regarding option D, acid-tolerant bacteria trigger ulcers (although acid can help); and option E happens continuously and is not related to release of HCl. 8

9. Stomach acid splits polypeptides into amino acids.
splits fats into fatty acids and glycerol.
activates pepsinogen into pepsin.
initiates the development of stomach ulcers.
inhibits the production of epithelial cells. 9

10. Secretin modulates digestion by
acting as an enzyme in the duodenum.
triggering bile release into the intestine.
triggering buffer release from the pancreas.
acting as an enzyme in the stomach.
triggering acid release in the stomach.
Answer: c
In response to acidic chyme, secretin is produced in intestinal cells, circulates in the blood, and triggers the pancreas to release sodium bicarbonate (Figure 41.20). Option A does not occur; B is true of CCK, not secretin; regarding D, secretin slows down stomach activity; and E is true of gastrin, not secretin. 10

11. Secretin modulates digestion by
acting as an enzyme in the duodenum.
triggering bile release into the intestine.
triggering buffer release from the pancreas.
acting as an enzyme in the stomach.
triggering acid release in the stomach. 11

12. The bile salts function in fat digestion by
hydrolyzing fat molecules to glycerol and fatty acids.
separating individual fat molecules from each other.
dissolving fats in water.
dispersing big droplets of fats to small droplets.
triggering the secretion of pancreatic lipase.
Answer: d
This question relates to Concept When fat globules enter the small intestine, they are mixed with water and bile salts. Bile salts coat smaller fat globules, emulsifying them. Options B and C do not occur in water. 12

13. The bile salts function in fat digestion by
hydrolyzing fat molecules to glycerol and fatty acids.
separating individual fat molecules from each other.
dissolving fats in water.
dispersing big droplets of fats to small droplets.
triggering the secretion of pancreatic lipase. 13

14. A fatty acid absorbed into an intestinal cell
is hydrolyzed to smaller fragments.
enters a lacteal vessel as a carbohydrate.
becomes part of a chylomicron.
is bound to bile salts.
exits the cell to directly enter the blood.
Answer: c
This question relates to Concept Fats are insoluble in water, and fat droplets are too large to pass through the membranes of capillaries, so chylomicrons enter the lacteal vessels of the lymph system. 14

15. A fatty acid absorbed into an intestinal cell
is hydrolyzed to smaller fragments.
enters a lacteal vessel as a carbohydrate.
becomes part of a chylomicron.
is bound to bile salts.
exits the cell to directly enter the blood. 15

16. Mutualistic bacteria aid digestion in many herbivores, including those where this function resides primarily in the large intestine, as in the
cow.
sheep.
goat.
horse.
deer.
Answer: d
All other choices are ruminants (“front-end fermenters”). 16

17. Mutualistic bacteria aid digestion in many herbivores, including those where this function resides primarily in the large intestine, as in the
cow.
sheep.
goat.
horse.
deer. 17

18. Glucagon, the pancreatic hormone, functions to
stimulate hunger.
inhibit activity in the small intestine.
increase fat storage in fat cells.
reduce glucose levels in the blood.
stimulate the liver to release glucose.
Answer: e
This question relates to Concept 41.5. 18

19. Glucagon, the pancreatic hormone, functions to
stimulate hunger.
inhibit activity in the small intestine.
increase fat storage in fat cells.
reduce glucose levels in the blood.
stimulate the liver to release glucose. 19

20. Increased appetite is the typical result of increased levels in the blood of
leptin.
PYY.
ghrelin.
insulin.
secretin.
Answer: c
Ghrelin is released in greater quantities by an empty, shrunken stomach than by a full stomach. Leptin (A), PYY (B), and insulin (D) are associated with satiety, not hunger. Secretin (E) is not linked to appetite regulation. The regulation of appetite is explained in Concept 41.5. 20

21. Increased appetite is the typical result of increased levels in the blood of
leptin.
PYY.
ghrelin.
insulin.
secretin. 21

22. Increased glucose levels in blood, after a meal, trigger
glucagon release from the pancreas.
insulin release from the pancreas.
secretin release from the duodenum.
cholecystokinin release from the pancreas.
activation of amylase in the blood.
Answer: b
This question relates to Concept The main response to high blood glucose is release of pancreatic insulin, triggering its target cells to take up the excess glucose. Glucagon secretion will be reduced during this time. Secretin and cholecystokinin are digestive hormones, not related to blood glucose levels. Amylase is a digestive enzyme mainly in saliva, not in the blood. 22

23. Increased glucose levels in blood, after a meal, trigger
glucagon release from the pancreas.
insulin release from the pancreas.
secretin release from the duodenum.
cholecystokinin release from the pancreas.
activation of amylase in the blood. 23

24. In which of the following structures does absorption of water, vitamin K, and salt occur?
large intestine
small intestine
liver
stomach
pancreas
Answer: a
The final absorption of those three key elements occurs in the large intestine. This is why treatment of diarrhea, which is watered-down stool from rapid expulsion of food from the body, includes replenishing water, sodium, and potassium immediately. 24

25. In which of the following structures does absorption of water, vitamin K, and salt occur?
large intestine
small intestine
liver
stomach
pancreas 25

26. Which of the following organisms is most likely to have an extremely large cecum?
carnivore
ruminant herbivore
nonruminant herbivore
insectivore
Answer: c
Nonruminant herbivores need more surface area for digestion of cellulose in plants they consume. 26

27. Which of the following organisms is most likely to have an extremely large cecum?
carnivore
ruminant herbivore
nonruminant herbivore
insectivore 27

28. Scientific Skills Exercises
Researchers hypothesized that the wild-type ob  and db genes participate in a hormone pathway that suppresses appetite when caloric intake is sufficient. To test this hypothesis, they measured the mass of young mice (“subject mice”) of various genotypes and surgically linked the circulatory system of each subject mouse to that of another mouse. This procedure ensured that any substance circulating in the bloodstream of either mouse would be transferred to the other. All of the subject mice were given unlimited access to food and water. After eight weeks, the researchers again measured the mass of each subject mouse.

29. The table shows the data from the experiment.

30. Which of the following statements about the genotype pairings is correct?
a) Pairing (a) joined two mice that were mutants for both the ob and db genes.
b) Pairing (b) joined two mice that were mutants for the ob gene but wild-type for the db gene.
c) Pairing (c) joined a wild-type mouse with one that was a mutant for the db gene.
d) Pairing (d) joined a wild-type mouse with one that was a mutant for the db gene.
Answer: b

31. Which of the following statements about the genotype pairings is correct?
a) Pairing (a) joined two mice that were mutants for both the ob and db genes.
b) Pairing (b) joined two mice that were mutants for the ob gene but wild-type for the db gene.
c) Pairing (c) joined a wild-type mouse with one that was a mutant for the db gene.
d) Pairing (d) joined a wild-type mouse with one that was a mutant for the db gene.

32. In what way did pairing (a) serve as a unique experimental control?
a) Only in pairing (a) were the subject mice joined surgically to other mice.
b) Only in pairing (a) were both mice wild-type for both genes.
c) Only in pairing (a) were the subject mice provided with unlimited access to food and water.
d) Only in pairing (a) were changes in the body mass of the subject mice calculated.
Answer: b

33. In what way did pairing (a) serve as a unique experimental control?
a) Only in pairing (a) were the subject mice joined surgically to other mice.
b) Only in pairing (a) were both mice wild-type for both genes.
c) Only in pairing (a) were the subject mice provided with unlimited access to food and water.
d) Only in pairing (a) were changes in the body mass of the subject mice calculated.

34. Based on the data shown in the table, which of the following is a reasonable conclusion about the wild-type gene products?
a) The db+ gene product had no effect on the results of the experiment.
b) The ob+ gene product had no effect on the results of the experiment.
c) The ob+ gene product did not circulate to the mutant mice when they were paired with wild-type mice.
d) The ob+ gene product circulated between both mice in a pair, even when only one mouse was wild-type for that gene.
Answer: d

35. Based on the data shown in the table, which of the following is a reasonable conclusion about the wild-type gene products?
a) The db+ gene product had no effect on the results of the experiment.
b) The ob+ gene product had no effect on the results of the experiment.
c) The ob+ gene product did not circulate to the mutant mice when they were paired with wild-type mice.
d) The ob+ gene product circulated between both mice in a pair, even when only one mouse was wild-type for that gene.

36. Compare the result for pairing (b) with the result for pairing (c)
Compare the result for pairing (b) with the result for pairing (c). What effect does the ob+ gene product appear to have on appetite?
a) The ob+ gene product promotes appetite.
b) The ob+ gene product suppresses appetite.
c) The ob+ gene product neither promotes nor suppresses appetite.
Answer: b

37. Compare the result for pairing (b) with the result for pairing (c)
Compare the result for pairing (b) with the result for pairing (c). What effect does the ob+ gene product appear to have on appetite?
a) The ob+ gene product promotes appetite.
b) The ob+ gene product suppresses appetite.
c) The ob+ gene product neither promotes nor suppresses appetite.

38. Note that the subject mice gained much more mass in pairing (b) than in pairing (a), whereas the subject mice in pairing (d) lost mass. Which of these hypotheses could explain the result for pairing (d)?
a) The db+ gene product is the receptor for the ob+ satiety factor; the db mutant in pairing (d) cannot receive this receptor through the circulation and therefore overproduces the ob+ satiety factor.
b) The db+ gene product is the receptor for the ob+ satiety factor; the db mutant in pairing (d) receives this receptor from its partner through their shared circulatory system.
c) The db+ gene product is another satiety factor; it suppresses appetite like the satiety factor encoded by the ob+ gene.
Answer: a

39. Note that the subject mice gained much more mass in pairing (b) than in pairing (a), whereas the subject mice in pairing (d) lost mass. Which of these hypotheses could explain the result for pairing (d)?
a) The db+ gene product is the receptor for the ob+ satiety factor; the db mutant in pairing (d) cannot receive this receptor through the circulation and therefore overproduces the ob+ satiety factor.
b) The db+ gene product is the receptor for the ob+ satiety factor; the db mutant in pairing (d) receives this receptor from its partner through their shared circulatory system.
c) The db+ gene product is another satiety factor; it suppresses appetite like the satiety factor encoded by the ob+ gene.

40. If the results had been identical for pairings (a) and (b), what conclusion would you have drawn?
a) Differences in ob genotype account for the observed change in body mass.
b) Differences in db genotype account for the observed change in body mass.
c) Differences in ob genotype do not affect the change in body mass of the mice.
Answer: c

41. If the results had been identical for pairings (a) and (b), what conclusion would you have drawn?
a) Differences in ob genotype account for the observed change in body mass.
b) Differences in db genotype account for the observed change in body mass.
c) Differences in ob genotype do not affect the change in body mass of the mice.