Answers to Mastering Concepts Questions

28.1
1. What does it mean for an organism to maintain homeostasis?

Homeostasis means the organism is maintaining a constant internal environment.

2. How do different habitats select for unique adaptations?

Environmental conditions vary across the globe.  In each environment, maintaining homeostasis is essential to survival.  Homeostatic processes might vary between individuals, though. For example, organisms adapted to cold weather likely have more elaborate behaviors and physiological processes to remain warm than organisms adapted to warm weather. 

28.2
1. Describe the difference between endotherms and ectotherms.

Ectotherms use the environment, not their own internal mechanisms, to regulate their body temperature.  Endotherms regulate their body temperature through internal mechanisms.

2. What are the advantages and disadvantages of endothermy and ectothermy?

Ectothermy requires less food and oxygen than does endothermy. One disadvantage of ectothermy, however, is that an animal must be able to successfully complete the behaviors needed to raise or lower its body temperature. Ectotherms also become sluggish at low temperatures. Endotherms are typically more active animals, but they require much more food and oxygen than do ectotherms.

28.3
1. What are two reasons that animals must eat?

Animals must eat to obtain energy and to obtain the raw materials for building the tissues of the body.

2. Explain the 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.

28.4
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.

28.5
1. 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).

2. What is body mass index?

Body mass index (BMI) 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.

3. Describe the events of starvation.

After day 1 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.

4. What are some of the causes and effects of obesity?

Obesity is caused by a person eating more calories than he or she uses. A diet high in sugar and fat, combined with an inactive lifestyle, leads to obesity; genes play a role as well. Obesity is related to type 2 diabetes, high blood pressure, atherosclerosis, congestive heart failure, acid reflux disease, urinary incontinence, low back pain, stroke, sleep disorders, and cancers of the colon, breast, and uterus.

28.6
1. Define the terms herbivore, carnivore, detritivore, and omnivore.

Herbivores eat only plants. Carnivores eat other animals. Detritivores eat decomposing organic matter. Omnivores eat a broad variety of foods.

2. What four processes does food undergo when an animal eats?

When an animal eats, food undergoes ingestion, digestion, absorption, and elimination.

3. Distinguish between intracellular and extracellular digestion.

Intracellular digestion happens in food vacuoles of individual cells. Extracellular digestion happens in body cavities connected to the outside world.

4. How do incomplete and complete digestive tracts differ?

An incomplete digestive tract has one opening, while a complete tract has two.

5. Compare and contrast the digestive systems of an elk and a wolf.

An elk is a ruminant. It has a rumen, where grass is digested by microorganisms. Overall the digestive tract is long, and the cecum is large. A wolf is a carnivore. Its digestive tract is short, and the cecum is small.

28.7
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 in digestion.

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. How does food move from the mouth to the stomach?

The rhythmic smooth muscle contractions of peristalsis propel food along the esophagus from the mouth to the stomach.

4. Describe the mechanical and chemical 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.

5. What is the structure and function of the small intestine?

The first segment of the small intestine is the duodenum.  It receives food from the stomach and secretes a mucus to protect the small intestine from the acid of the stomach. The small intestine digests and absorbs the nutrients in food. The small intestine maximizes surface area because the inner surface of the small intestine is folded 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 acids in the intestine.  The liver produces bile that emulsifies fats, and the gall bladder 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. Cellulose, bacteria, and intestinal cells collect in the rectum as feces.

8. How does undigested food leave the body?

Undigested food is eliminated as feces from storage in the rectum.

28.8
1. What is the main nitrogenous waste in a mammal’s urine?

Urea is the nitrogenous waste in mammalian urine.

2. Explain how osmoregulation occurs in marine and freshwater fish.

Marine fish must conserve water and get rid of excess salts. They drink seawater, have low urine volume, and use active transport to remove salt at the gills.  Freshwater fish must conserve salts and get rid of excess water. They take in a lot of water through their skin and gills by osmosis, and excrete the excess in their urine. They also use active transport to take ions in through the gills.

28.9
1. List the organs that make up the human urinary system.

The organs of the human urinary system are the kidneys, ureters, urinary bladder, and urethra.

2. What are the functions of the kidneys?

The kidneys remove urea from the bloodstream and maintain the proper concentrations of water, salt, and ions in the bloodstream. The kidneys also regulate blood pH.

28.10
1. Trace the path of blood as it moves through a kidney.

As blood moves through a kidney, it follows this path: renal artery – incoming arteriole – glomerulus – outgoing arteriole – peritubular capillary – venule – renal vein – back to the heart.

2. What is a nephron?

The parts of the nephron are the glomerular capsule, the proximal convoluted tubule, the nephron loop, and the distal convoluted tubule

3. What three processes occur in urine formation?

The three processes are filtration, reabsorption, and secretion.

4. What is the function of the collecting duct?

The collecting duct receives the fluid from many nephrons and continues to concentrate the urine by reabsorbing more water into the blood.

5. Describe the roles of antidiuretic hormone and aldosterone in regulating kidney function.

Antidiuretic hormone stimulates the formation of water channels in the walls of the distal convoluted tubule and collecting duct, reducing urine volume by causing more water to be reabsorbed into blood.  Aldosterone also conserves water and boosts blood pressure by stimulating the formation of sodium channels in the distal convoluted tubule, causing sodium to be reabsorbed into the blood. Water follows by osmosis.

28.11
1. How did researchers use nasal cavities to draw their conclusions?

The researchers measured the cross-sectional area of the nose.  A larger nasal cavity should be present if the animal needed to breathe more.  An increase in breathing rate would be present in endotherms.

2. Suppose a fossil of a 100-kilogram dinosaur has a nasal cavity greater than 10 square centimeters. According to figure 28.28, would that finding affect Ruben’s conclusions?

Such a fossil would suggest the presence of endothermy in some dinosaurs and would lead to a different conclusion, perhaps that the evolution of feathers and endothermy went hand-in-hand.

 

Answers to Write It Out Questions

1. How do humans and snakes differ in body temperature regulation?

Snakes are ectotherms; they lack an internal temperature-regulating mechanism so they must move to areas where they can gain or lose heat. Humans are endotherms; we regulate body temperature internally to maintain a relatively constant body temperature. 

2. Birds and insects frequently collect nectar from plants. Birds are endothermic, and insects are ectothermic. For the same investment of nectar, do you think a plant can support a greater mass of insects or of birds?

For the same investment of nectar, a plant could support a greater mass of insects than birds because ectotherms use much less energy and, therefore, require less food than do endotherms.

3. Would an alligator require more, less, or the same amount of food as a horse of the same size? Explain.

Because it is ectothermic, an alligator 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

4. Woolly mammoths are extinct relatives of modern-day elephants. The mammoths were heavier and shaggier than elephants, their ears were smaller, and they had a thick fat layer under their skin. Explain each of these differences in light of the fact that today’s elephants originate in Asia and Africa, whereas mammoths lived on the tundra.

On the tundra, the temperatures are much colder than they are in Asia and Africa. The mammoths’ extra body mass reduced the surface area relative to the animal’s volume, reducing heat loss to the environment. Fat and the shaggy coat added insulation. The smaller ears presented less surface area for heat loss.

5. 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.

6. What is the difference between a macronutrient and a micronutrient? Give examples of each.

A macronutrient is a nutrient that is required in large amounts, such as carbohydrates, proteins, and lipids. Micronutrients are required in smaller amounts; examples are vitamins, zinc, and iodine.

7. What determines whether a person will gain, lose, or maintain weight?

A change in a person’s weight is determined by the balance between caloric intake and activity level.  Intake of more calories than the body uses will result in weight gain; eating fewer calories than the body uses results in weight loss.

8. 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.

9. Calculate your body mass index using the formula in the text. How could you change your BMI?

[See text for formula.]  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.

10. Nutritional scoring systems rate foods according to their nutritional value. The table below lists sample values from the NuVal system, which rates foods on a scale of 1 (least healthy) to 100 (healthiest). Search the Internet to learn what information researchers use in calculating the score for each food. Browse the scores for your favorite foods. Which foods that you eat have the highest scores? The lowest? How might you use these scores to adjust your shopping and eating habits?

The scoring system considers over 30 different macro and micronutrients and the influences those nutrients have on long term health.  [Rest of answer will vary.]

11. Fructose and glucose are both monosaccharides, but the body metabolizes these sugars differently. For example, glucose stimulates insulin release from the pancreas (see chapter 25); fructose does not. Moreover, insulin stimulates leptin release. Use this information to propose an explanation for the correlation between the skyrocketing consumption of high fructose corn syrup since 1970 and the rise in obesity during the same period.

In the presence of insulin, glucose is absorbed into cells and used in cellular respiration. If fructose doesn’t stimulate insulin release, then it isn’t absorbed into cells and goes directly to the liver for conversion to fat (which also happens to excess glucose).  Also, with less leptin to reduce the appetite, calorie intake may be too high. Both effects could contribute to obesity.

12. What are the four stages of food use in animals and where in the human digestive tract does each of these stages 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).

13. Compare and contrast the digestive systems of a whale and a sponge.

The two types of organisms ingest, digest, absorb, and eliminate, but the structures that perform these functions are different.  The sponge will filter the water column and absorb the nutrients by the collar cells.  Whales have a complete digestive tract with two openings.  They ingest food through the mouth and digest the food inside the digestive tract.  Cells lining the digestive tract absorb the nutrients, and then waste is eliminated through the anus. 

14. Name an organism that has each of the following: extracellular digestion; an alimentary canal; a gastrovascular cavity.

Answers will vary, but some examples are: humans; humans; jellyfish.

15. How is a carnivore’s digestive system different from that of an herbivore?

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.

16. How does mechanical breakdown of food speed chemical digestion?

The mechanical breakdown of food increases the surface area available for chemical digestion. 

17. Identify the part of the digestive system that includes the following: duodenum; cecum, appendix, rectum, and anus; villi and microvilli.

Duodenum:  small intestine
Cecum, appendix, rectum, and anus:  large intestine
Villi and microvilli:  small intestine

18. List the main parts of the human digestive system, then create a chart that compares the locations, anatomy, and functions of each part.

Structure	Location	Anatomy	Functions
Mouth	Head	Teeth, salivary glands, tongue	Moistens and tears food, starts carb digestion
Esophagus	Between mouth and stomach	Long tube; smooth muscle in wall	Propels food to stomach
Stomach	Between esophagus and small intestine	Cells that produce gastric juice; smooth muscle	Mixes food with gastric juice; begins protein digestion
Small intestine	Between stomach and large intestine	Villi, microvilli	Digests and absorbs all nutrients
Large intestine	End of digestive tract	Cecum, appendix, colon, rectum	Completes nutrient and water absorption

19. Trace the movement of food in the 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 the anal canal.

20. How does the structure of the small intestine maximize surface area?

The small intestine is lined with folds, each of which is covered with villi. Each villus has many projections called microvilli.

21. What are the digestive products of carbohydrates, proteins, and fats?

The digestive products of carbohydrates are monosaccharides; the products of protein digestion are amino acids; and the products of fat digestion are fatty acids and monoglycerides.

22. Compare and contrast the alveoli of the lungs (see chapter 27) with the villi of the small intestine.

The alveoli in the lungs function in gas exchange, and the villi in the small intestine absorb digested food molecules.  In both cases, substances pass across cell membranes, and both alveoli and villi have an enormous amount of surface area.

23. How do the circulatory and muscular systems interact with the digestive system?

The circulatory system interacts with the digestive system when blood picks up nutrients from the digestive system and transports them to all other parts of 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.

24. How does it benefit an organism to have a digestive system with an extensive surface area?

The greater the surface area, the more nutrients can be absorbed into the bloodstream for use in the body.

25. 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. 

26. 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 through the intestinal tract and out the other end.  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.

27. Imagine you are adrift at sea. If you drink seawater, you will dehydrate much faster than if you have access to fresh water. Explain.

Drinking salty water will cause your cells to lose water by osmosis, and you will rapidly become dehydrated.  Drinking fresh water will have the opposite effect; your cells will absorb water by osmosis.

28. List the organs that make up the human urinary system. What is the function of each?

Kidneys—form urine, regulate blood volume, conserve ions and nutrients, regulate blood pH
Ureter—carries urine from the kidneys to the bladder
Urinary bladder—stores urine
Urethra—transports urine from the bladder to the outside of the body

29. Kidney stones are calcium-rich crystals that form inside the kidney. What symptoms would you expect if the stones lodge in a ureter?

If the stones lodge in a ureter, symptoms might include blocked urine flow, pain, and bleeding from the walls of the urinary tract.

30. Shortly after you drink a large glass of water, you will feel the urge to urinate. Explain this observation. Begin by tracing the path of the water, starting at the stomach and ending with the arrival of urine in the bladder.

You will feel the urge to urinate shortly after you drink a large glass of water because the water causes the blood to be too dilute; the kidneys subsequently remove the excess water from the blood. The excess water first moves into the bloodstream and then passes through nephron filter to the nephron, where some is reabsorbed into the blood.  From the nephron, the fluid moves to the collecting duct, a ureter, and then into the urinary bladder.

31. How does the kidney reduce the volume of urine to a small fraction of the volume of filtrate that enters the nephron?

Capillaries surrounding the nephron reabsorb most of the water that enters the nephron filter.  Ion gradients cause water to move from the nephron into the blood by osmosis.  Because of this process, once the filtrate has passed through the nephron, most of the water in the original filtrate has been reabsorbed.

32.  Why is protein in the urine a sign of kidney damage? What structures in the kidney are probably affected?

Ordinarily, plasma proteins are too large to fit through the pores of the nephron filter.  Their presence in urine suggests, therefore, damage to the filter.

33. How could very low blood pressure impair kidney function?

Blood pressure drives substances from the bloodstream into the nephron. If blood pressure is very low, fluid will not enter the nephrons to be cleansed, and wastes could build up in the bloodstream to toxic levels.

34. Which of the substances in the following table are excreted in urine, and which are reabsorbed into the bloodstream?

Urea, uric acid, and creatinine are all excreted.  Glucose is reabsorbed into the bloodstream.

35. Many pharmaceutical drugs leave the body in urine. As we age, the number of nephrons in the kidneys declines. Do you predict that an older person would need a higher or lower dose of a drug to compensate for the amount lost in urine? Explain your answer.

A person with fewer nephrons would be less efficient at cleansing the blood of the drug.  He or she would, therefore, need a lower dose of the drug.

36. Review the action of steroid and peptide hormones in chapter 25.  Which hormone should act faster, ADH or aldosterone?  Why?

ADH is a peptide hormone, so it is water soluble. Aldosterone is a steroid hormone. In general, peptide hormones act more rapidly than do steroid hormones, so ADH should have faster effects.

37. In a disease called diabetes insipidus, ADH activity is insufficient. Would a person with this disease produce more or less urine than normal? Explain.

A person with insufficient ADH would produce more urine than normal, because ADH secretion conserves water. 

38. Use the Internet to find a list of diseases of the kidneys or other organs of the urinary system. Select one to research further. What causes the illness you chose, and what are the symptoms? How does the disease interfere with the function of the urinary system? Is there a treatment or cure? Who is most at risk of the disease?

[Answers will vary.]

 

Answers to Pull it Together Questions

1. Add the terms ingestion, digestion, absorption, elimination, chyme, bacteria, and peristalsis to this concept map.

"Ingestion" connects with the phrase "occurs at" to "Mouth". "Digestion" connects with the phrase "occurs at" to "Mouth", "Stomach", and "Small intestine". "Absorption" connects with the phrase "occurs at" to "Small intestine" and "Large intestine".  "Elimination" connects with the phrase "occurs at the end of the" to "Large intesine". "Chyme" connects with the phrase "is partially digested food in the" to "Stomach" and "Small intestine". "Bacteria" connects with the phrase "occupy the" to "Large intestine". "Peristalsis" connects with "propels food along the" to "Digestive system".

2. What are the accessory organs required for digestion?  Add them to this concept map.  What is the function of each?

"Salivary glands" connects with the phrase "release saliva in the" to "Mouth". "Liver" connects with the phrase "produces" to "Bile", which connects with the phrase "which emulsifies fat in the" to "Small intestine". "Gallbladder" connects with the phrase "stores" to "Bile". "Pancreas" connects with the phrase "releases digestive enzymes and bicarbonate into the" to "Small intestine". "Appendix" connects with the phrase "extends from the" to "Large intestine".

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.

4. What are the functions of filtration, secretion, and reabsorption in the nephron?

Filtration occurs at the head of the nephron and removes substances from the blood. Secretion occurs throughout the nephron tubules, moving substances into the tubules that are too large to be filtered. Reabsorption also occurs in the nephron tubules, moving materials back into the blood stream.

5. How do collecting ducts fit into this concept map?

"Nephrons" connects with the phrase "release urine into" to "Collecting ducts", which could further connect with the phrase "which empty into the upper portion of the" to "Ureters".

6. What is the relationship between the kidneys, ureters, bladder, and urethra?

Kidneys release urine into the ureters, which squirt the urine into the muscular bladder. Urine then leaves the body via the urethra.

7. How do aldosterone and antidiuretic hormone influence kidney function?

Both hormones act on the kidney to conserve water.  Aldosterone causes the nephron tubules to produce additional sodium channels; water follows the sodium by osmosis and enters the bloodstream.  ADH stimulates the kidneys to produce more water channels in the nephrons and collecting ducts, so more water enters the bloodstream.