Download Answers to Mastering Concepts Questions

Mastering Concepts
32.1
1. What are two reasons that animals must eat?
An animal must eat to obtain energy and the raw materials for building its body.
2. Explain three factors that affect an animal’s metabolic rate.
One factor determining metabolic rate is whether the organism is endothermic or
ectothermic; endotherms require more energy than ectotherms of equal size. Another
factor is body size; small animals need more energy per gram than large animals. A final
factor is physiological state; a growing animal requires more energy than an adult.
3. What are the four stages of food use in animals, and where in the human digestive tract
does each stage occur?
The four stages of food use in animals are ingestion (in the mouth); digestion (in the
mouth, stomach, and small intestine); absorption (in the small and large intestines); and
elimination (at the anus).
4. How does the mechanical breakdown of food speed chemical digestion?
The mechanical breakdown of food increases the surface area available for chemical
digestion.
4. Define the terms herbivore, carnivore, detritivore, and omnivore.
Herbivores eat plants. Carnivores eat other animals. Detritivores eat decomposing organic
matter. Omnivores eat a broad variety of foods.
32.2
1. Distinguish between intracellular and extracellular digestion.
Intracellular digestion happens in food vacuoles of individual cells. Extracellular
digestion happens in body cavities connected with the outside world.
2. How is an incomplete digestive tract different from a complete digestive tract?
An incomplete digestive tract has one opening, through which an animal both ingests
food and eliminates wastes. A complete digestive tract has two openings (mouth and
anus).
3. Compare and contrast the digestive systems of herbivores and carnivores.
Herbivores may or may not have a rumen, where microorganisms digest grass. Overall
the digestive tract is long, and the cecum is large. A carnivore has a short digestive tract
and the cecum is small.
32.3
1. Explain the action and importance of peristalsis and sphincters in digestion.
Peristalsis is the wave of muscular contraction that moves food along the digestive tract.
Sphincters are muscular rings that open and close to allow or block the passage of food
between areas of the digestive system.
2. Describe the functions of saliva, teeth, and the tongue.
Saliva moistens food and mixes it with salivary amylase, the enzyme that initiates
carbohydrate breakdown. The teeth grasp and chew food, mechanically breaking it down
to increase surface area. The tongue mixes the food with saliva and pushes the food to
the back of the mouth for swallowing.
3. Describe the digestion that occurs in the stomach.
Mechanical digestion occurs when muscle contractions in the stomach churn and further
break up the chewed food. Chemical digestion of proteins (by pepsin) begins in the
stomach.
4. What is the function of the small intestine?
The small intestine digests and absorbs the nutrients in food.
5. How does the small intestine maximize surface area?
The inner surface of the small intestine is folded into ridges, each of which is covered
with finger-like villi. In addition, the surface of each villus has hundreds of microvilli that
greatly increase the surface area for absorption.
6. How do the pancreas, liver, and gallbladder aid digestion?
The pancreas secretes the majority of the digestive enzymes and the bicarbonate that
neutralizes stomach acid in the intestine. The liver produces bile that emulsifies fats, and
the gallbladder stores and releases the bile.
7. Describe the events that occur as food passes through the large intestine.
As food passes through the large intestine, water, salts, and minerals are absorbed from
chyme. Indigestible substances, bacteria, and intestinal cells collect in the rectum as
feces.
32.4
1. Which nutrients are macronutrients and which are micronutrients?
The macronutrients are water, carbohydrates, proteins, and lipids. Micronutrients include
minerals and vitamins.
2. How does indigestible fiber contribute to a healthy diet?
Indigestible fiber provides bulk and eases movement of food in the digestive tract. Fiber
also reduces blood cholesterol and helps to regulate blood sugar.
3. Describe the relationship of body weight to calorie intake and energy expenditure.
If calories taken in are balanced by energy expenditure, then weight will remain constant.
If there is an imbalance, then weight will go up (excess intake) or go down (excess
expenditure).
4. What is body mass index?
Body mass index is one way to determine if a person’s weight is healthy. To calculate
BMI, divide a person’s weight in kilograms by his or her height in meters, squared.
32.5
1. How did the response of Spea tadpoles to shrimp differ from that of Scaphiopus?
Spea tadpoles developed a significantly shorter gut when given shrimp than when they
received fish food. In contrast, Scaphiopus tadpoles fed shrimp did not significantly differ
in gut length compared to those given fish food.
2. Why is it adaptive for gut length in amphibian tadpoles to differ from generation to
generation, depending on the environment?
Developing a gut of appropriate length optimizes energy balance. The gut is expensive to
produce and maintain, so having a too-long gut wastes energy. On the other hand, a tooshort gut could mean that some food does not get fully digested. Since some
environments, such as that of spadefoot toads, change from generation to generation, it is
adaptive for the tadpoles of these amphibians to adjust their gut length to the current food
availability.
Write It Out
1. What are the two main functions of food in an animal’s body?
Food supplies potential energy that an animal uses to generate ATP, and it supplies the
raw materials that the animal’s body needs to produce its own molecules.
2. Does an alligator require more, less, or the same amount of food as a horse of the same
size? Explain.
An alligator is ectothermic, so it would need less food than a horse of the same size. The
horse requires extra food to generate the energy needed to maintain a constant body
temperature.
3 Biologists estimate that carnivores assimilate 90% of the mass in their diet; in contrast,
most herbivores assimilate only 30% to 60% of their food. How do these differences in
assimilation efficiency relate to the structure of their digestive systems?
Plant material is harder to digest than is the meat in a carnivore’s diet. Herbivores have
longer digestive tracts and a larger cecum than do carnivores. The longer digestive tract
means the food has more time to digest. Microbes in the cecum ferment plant material
that the animal cannot digest on its own, releasing extra nutrients.
4. Trace the movement of food in the human digestive tract from mouth to anus.
Food moves from the mouth to the esophagus, to the stomach, through the pyloric
sphincter to the small intestine, to the large intestine, and then through the rectum and out
through the anus.
5. Fast food restaurants in the United States must display calorie counts for their menu
items. Speculate about whether knowing the caloric content of food will change
consumers’ food choices. If buyers did consider calories when making purchases, could
the incidence of obesity in the United States decrease?
Answers will vary. Some analysts speculate that calorie contents displayed on menus will
make the United States a healthier country, since eating more calories than are needed
causes weight gain. Others speculate that when people choose fast food restaurants, they
are planning to eat unhealthy food, so displaying the calories will not make a difference.
6. Orlistat (Alli) is a weight-loss drug that inhibits the activity of lipases in the small
intestine. Why would this be more effective than a drug that blocks absorption of proteins
or carbohydrates? Given that four essential vitamins are fat-soluble, what might be a side
effect of blocking fat absorption?
A gram of fat contains more calories than a gram of protein or carbohydrate, so a drug
that blocks fat digestion would “save” the most calories. The side effect of blocking fat
absorption would probably be oily feces and reduced absorption of fat-soluble vitamins.
7. Describe the events of starvation.
After a day without food, sugar and glycogen reserves are depleted, and the body begins
breaking down stored fat and muscle protein. As starvation continues over many days
and weeks, the body digests itself, deriving energy and protein from muscles, antibodies,
skin, stored fat, and bones. Near the end, the starving human is blind, deaf, and
emaciated.
8. Write down the foods you ate today, and use nutrition labels to determine how many
calories you consumed. Then, use calculators on the Internet to estimate how many
calories you require each day based on your age, weight, gender, and activity level. Did
you consume more or fewer calories than you needed? If you repeated these eating habits
for several weeks, would you gain or lose weight?
Answers will vary. If you consistently consume more calories than you need, then you
will gain weight. On the other hand, consuming fewer calories than required will lead to
weight loss.
9. Phytonutrients are plant-derived chemicals that are not essential to the human diet, but
they may improve health. Use the Internet to research a phytonutrient. What foods
contain the phytonutrient you selected? What diseases might consuming the nutrient help
to prevent?
Answers will vary. One example of a phytonutrient is resveratrol, which occurs in grapes
and red wine. It is an antioxidant that may reduce the risk of heart disease and cancer.
Other examples of phytonutrients include lutein, carotenoids, and flavonoids.
10. Calculate your body mass index using the formula in the text. How could you change
your BMI?
Answers will vary. The only way for an adult to change his or her BMI is to gain or lose
weight by altering food intake, exercise habits, or both.
11. Suppose you hope to determine if consuming sugary drinks each day leads to weight
gain. Design an experiment to test this prediction. How could you determine if the sugar
in the drink or simply consuming extra calories leads to weight gain?
Answers will vary; this is one example. The experiment should have at least two groups.
One group drinks the sugary beverage each day. A control group does not consume the
sugary drink. Weight changes through the experiment are measured in each group.
Standardizing the number of calories and the activity level of each participant (in both
groups) may help to determine if weight gain is due to the sugary drink or due to the
calories in the drink. It may also be useful to have a third experimental group that
consumes a drink that is high in protein and equal in calories to the sugary drink.
12. How do the circulatory and muscular systems interact with the digestive system?
The circulatory system interacts with the digestive system when blood carries nutrients
from the digestive system throughout the body. The muscular system interacts with the
digestive system as smooth muscle moves food along the digestive tract. In addition,
skeletal and smooth muscle control the mouth, tongue, esophagus, and anal sphincter.
13 Design an experiment to test the hypothesis that intestinal bacteria are essential to
nutrient absorption in mice.
A researcher could raise some mice in a microbe-free environment or use antibiotics to
kill intestinal microflora. A control group of genetically similar mice would have normal
microflora. The two groups of mice would receive the same diets, and then their blood
could be tested to determine whether they differ in nutrient absorption.
14. Many children believe that a piece of swallowed chewing gum will remain in the
body for 7 years. Chewing gum is made of an indigestible polymer that does not dissolve
in water. Since the gum cannot be digested, what happens to it after it is swallowed?
Given your answer, does the 7-year timescale make sense? Propose an alternative
prediction for how long it might take instead, and explain your reasoning.
No, this idea does not make sense. The gum may remain undigested, but it will move
with the rest of the food along the intestinal tract and out the anus with other indigestible
substances. One prediction for the time to elimination would be that the swallowed gum
would be eliminated with whatever else was ingested around the same time.
Pull it Together
1. Add the terms ingestion, digestion, absorption, elimination, chyme, bacteria, and
peristalsis to this concept map.
“Ingestion” connects with “occurs at the” to “mouth.” “Digestion” connects with “occurs
at the” to “mouth,” “stomach,” and “small intestine.” “Absorption” connects with “occurs
at the” to “small intestine” and “large intestine.” “Chyme” connects with “is partially
digested food in the” to “stomach,” “small intestine,” and “large intestine.” “Bacteria”
connects with “occupy the” to “large intestine.” “Peristalsis” connects with “propels food
along the” to “digestive system.”
2. Write a phrase that connects liver to gallbladder in the concept map. How would
removing the gallbladder affect the digestion of fats?
“Gallbladder” connects with the phrase “stores and releases bile produced by the” to
“liver.” Bile helps fat-digesting enzymes come into contact with fat; the gallbladder
stores bile until it is needed for digestion. Without the gallbladder, bile constantly trickles
into the small intestine as the liver produces it. Digesting high-fat meals may be difficult
for people that have had their gallbladder removed since bile is not released in response
to the meal.
3. In which organ(s) are carbohydrates, proteins, and fats digested?
Carbohydrates are digested in the mouth and small intestine. Proteins are digested in the
stomach and small intestine. Fats are digested in the small intestine.