1. Which of the following is NOT a method used in maintaining homeostasis in the body? a. Behavioral changes b. Negative feedback loops c. Hormonal actions d. Positive feedback loops
The correct answer is d—
A.
Answer a is incorrect. Behavioral changes (for example moving to a warmer or cooler area, or changes in body posture) is a method used by animals to maintain homeostasis.
The correct answer is d—
B.
Answer b is incorrect. Negative feedback loops are a mechanism used by animals to maintain homeostasis within the body. Negative feedback loops involve a stimulus, a response, and a processor that can recognize a stimulus. The response in a negative feedback loop has the net effect of removing the stimulus, which shuts of the processor and ends the response.
The correct answer is d—
C.
Answer c is incorrect. Hormones (the endocrine system) play an important role in maintaining homeostasis, particularly in long-term processes.
The correct answer is d—Positive feedback loops
D.
Answer d is correct. Positive feedback loops, although very important in certain circumstances (blood clotting, childbirth), tend to move body systems away from their normal setpoints.
2. Similarities between the invertebrate and vertebrate excretory systems include— a. filtering of body fluid b. use of tubules to contain filtrate c. reabsorption of ions and water d. all of the above
The correct answer is d—
A.
Answer a is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—
B.
Answer b is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—
C.
Answer c is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—all of the above
D.
Answer d is correct. It includes all of the correct responses to the question.

3. Suppose that your research mentor has decided to do a project on the filtering capabilities of Malpighian tubules. Which of the following creatures will you spend your summer studying? a. Ants b. Birds c. Mammals d. Earthworms
The correct answer is a — Ants
A.
Answer a is correct. Insects (ants) use Malpighian tubules to excrete wastes.
The correct answer is a—
B.
Answer b is incorrect. Birds, as vertebrates, use kidneys to excrete wastes.
The correct answer is a—
C.
Answer c is incorrect. Mammals, as vertebrates, use kidneys to excrete wastes.
The correct answer is a—
D.
Answer d is incorrect. Annelids (earthworms) use nephridia to excrete wastes.
4. A shark’s blood is isotonic to the surrounding seawater because of the reabsorption of ___________ in its blood. a. ammonia b. uric acid c. urea d. NaCl
The correct answer is c —
A.
Answer a is incorrect. Ammonia can be toxic if it builds up in body fluids. A safer alternative is urea.
The correct answer is c—
B.
Answer b is incorrect. Uric acid is synthesized from ammonia by reptiles and birds, not cartilaginous fish.
The correct answer is c—urea
C.
Answer c is correct. Unlike bony fish, sharks maintain their body fluids at levels isotonic to their environment by using urea.
The correct answer is c—
D.
Answer d is incorrect. Sharks do not use NaCl to maintain the isotonicity of their body fluids.

5. An important function of the excretory system is to eliminate excess nitrogen produced by metabolic processes. Which of the following organisms is most efficient at packaging nitrogen for excretion? a. Frog b. Freshwater fish c. Iguana d. Camel
The correct answer is c —
A.
Answer a is incorrect. Although frogs produce urea, which contains two nitrogen atoms per molecule, birds and lizards are more efficient. They produce uric acid, which contains four nitrogen atoms per molecule.
The correct answer is c—
B.
Answer b is incorrect. Fish release excess nitrogen as ammonia (one nitrogen) or urea, which contains two nitrogen atoms per molecule, birds and lizards are more efficient. They produce uric acid, which contains four nitrogen atoms per molecule.
The correct answer is c—Iguana
C.
Answer c is correct. Birds and lizards are more efficient than the other choices.
They produce uric acid, which contains four nitrogen atoms per molecule.
The correct answer is c—
D.
Answer d is incorrect. Mammals release excess nitrogen as urea, which contains two nitrogen atoms per molecule; however, birds and lizards are more efficient.
They produce uric acid, which contains four nitrogen atoms per molecule.
6. Which of the following is a function of the kidneys? a. The kidneys remove harmful substances from the body. b. The kidneys recapture water for use by the body. c. The kidneys regulate the levels of salt in the blood. d. All of these are functions of the kidneys.
The correct answer is d —
A.
Answer a is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—
B.
Answer b is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—
C.
Answer c is incorrect. It is only one of the three correct answers to this question.
The correct answer is d—All of these are functions of the kidneys.
D.
Answer d is correct. It includes all of the correct responses to the question.

7. A viral infection that specifically interferes with the reabsorption of ions from the glomerular filtrate would have attack cells located in the— a. Bowman’s capsule b. glomerulus c. renal tubules d. collecting duct
The correct answer is c—
A.
Answer a is incorrect. The Bowman’s capsule is the site of filtration not reabsorption.
The correct answer is c—
B.
Answer b is incorrect. The glomerulus is actually a formed from capillaries and does not contain filtrate.
The correct answer is c—
C.
Answer c is correct. Reabsorption occurs in the proximal tubule.
The correct answer is c—
D.
Answer d is incorrect. Reabsorption of ions does not occur in the collecting duct.
8. Humans excrete their excess nitrogenous wastes as— a. uric acid crystals b. compounds containing protein c. ammonia d. urea
The correct answer is d —
A.
Answer a is incorrect. Humans do not produce nitrogenous waste as uric acid.
The correct answer is d—
B.
Answer b is incorrect. A healthy glomerulus will retain proteins in the bloodstream. If fact, it is the breakdown of proteins that produces much of the excess nitrogen in the body.
The correct answer is d—
C.
Answer c is incorrect. Ammonia is too toxic to be allowed to circulate in the bloodstream until it reaches the kidney. Urea is a safer alternative.
The correct answer is d—urea
D.
Answer d is correct. Urea is less toxic than ammonia and contains more nitrogen, thereby allowing the kidney to increase its efficiency.
9. Which of the following statements is NOT true? a. ADH makes the collecting duct more permeable to water. b. Guano contains high concentrations of uric acid.

c. Aldosterone is produced by the hypothalamus in response to high levels of sodium ions in the blood. d. Uric acid is the least soluble of the nitrogenous waste products.
The correct answer is c —
A.
Answer a is incorrect. The hormone ADH (vasopressin) makes the collecting duct more permeable to water. Water leaks from the duct back into the tissues and eventually to the blood.
The correct answer is c —
B.
Answer b is incorrect. Guana (bird excrement) contains uric acid.
The correct answer is c—Aldosterone is produced by the hypothalamus in response to high levels of sodium ions in the blood.
C.
Answer c is correct. Aldosterone is a corticosteroid hormone released by the adrenal cortex.
The correct answer is c—
D.
Answer d is incorrect. Uric acid is the least soluble of the nitrogen waste products
(ammonia, urea, uric acid) and therefore allows birds and reptiles to conserve water from their waste.
10. The major difference between ectotherms and endotherms in terms of maintenance of body temperature is that— a. ectotherms rely solely on environmental conditions to determine body temperature b. endotherms are impervious to environmental conditions c. ectotherms rely more heavily on behavioral adaptations than do endotherms d. endotherms are larger than ectotherms
The correct answer is c—
A.
Answer a is incorrect. Ectotherms generate some heat as a result of metabolic processes (laws of thermodynamics). In addition, they use a variety of behaviors that allow them to mitigate heat gain or loss.
The correct answer is c—
B.
Answer b is incorrect. Endotherms are impervious to only a narrow range of temperatures. For example, what happens if you tried to walk around naked on a
40º (Fahrenheit) day?
The correct answer is c—ectotherms rely more heavily on behavioral adaptations than do endotherms
C.
Answer c is correct. Although both use behavior to control heat gain or loss, ectotherms rely on it more heavily.

The correct answer is c—
D.
Answer d is incorrect. Some endotherms are quite small (shrews, mice), and some ectotherms are quite large (fish, Komodo dragons).
11. An osmoregulator would maintain its internal fluids at a concentration that is
____________ relative to its surroundings. a. isotonic b. hypertonic c. hypotonic d. either hypertonic, hypotonic, or isotonic
The correct answer is d—
A.
Answer a is incorrect. An osmoregulator may maintain its internal concentrations at hypertonic, hypotonic, or isotonic levels, depending on its external environment.
The correct answer is d—
B.
Answer b is incorrect. An osmoregulator may maintain its internal concentrations at hypertonic, hypotonic, or isotonic levels, depending on its external environment.
The correct answer is d—
C.
Answer c is incorrect. An osmoregulator may maintain its internal concentrations at hypertonic, hypotonic or isotonic levels, depending on its external environment.
The correct answer is d—either hypertonic, hypotonic, or isotonic
D.
Answer d is correct. An osmoregulator may maintain its internal concentrations at hypertonic, hypotonic, or isotonic levels, depending on its external environment.
12. If humans are endotherms, why do conditions like hypothermia (low body temperature) and hyperthermia (high body temperature) occur? a. Mechanisms that control body heat are inefficient and allow large fluctuations in temperature b. Body heat is the sum of heat produced by metabolic reactions and the heat transferred from the environment c. Metabolic reaction rates may change due to illness or activity level d. Both b and c
The correct answer is d—
A.
Answer a is incorrect. Most endotherms are capable of maintaining their body temperatures within reasonable limits.
The correct answer is d—
B.
Answer b is incorrect. Environmental conditions play a role in determining body heat through heat gain or loss. However, answer b is incorrect because it is only one of two correct responses to the question.

The correct answer is d—
C.
Answer c is incorrect. Metabolic rates may change due to illness (fever) or activity (exercise) and consequently cause body temperature to move out of the normal range. However, answer c is incorrect because it is only one of two correct responses to the question.
The correct answer is d—Both b and c
D.
Answer d is correct. Environmental conditions play a role in determining body heat through heat gain or loss. Also, metabolic rate changes due to illness (fever) or activity (exercise) may consequently cause body temperature to move out of the normal range.
13. You and your study partner want to draw the pathway that controls the reabsorption of sodium ion when blood pressure falls. Which of the following is the correct sequence of events?
1.
Aldosterone is released
2.
Kidney tubules reabsorb Na
+
3.
Renin is released
4.
Juxtaglomerular apparatus (JGA) recognizes a drop in blood pressure
5.
Angiotensin II is produced a. 1, 3, 5, 2, 4 b. 4, 2, 3, 1, 5 c. 4, 3, 5, 2, 1 d. 2, 4, 3, 1, 5
The correct answer is c—
A.
Answer a is incorrect. The correct order begins with a drop in blood pressure recognized by the JGA (4), followed by the release of rennin (3), angiotensin II production (5), aldosterone release (1), kidney tubule reabsorption of Na
+
(2).
The correct answer is c—
B.
Answer b is incorrect. The correct order begins with a drop in blood pressure recognized by the JGA (4), followed by the release of rennin (3), angiotensin II production (5), aldosterone release (1), kidney tubule reabsorption of Na
+
(2).
The correct answer is c—4, 3, 5, 2, 1
C.
Answer c is correct. The correct order begins with a drop in blood pressure recognized by the JGA (4), followed by the release of rennin (3), angiotensin II production (5), aldosterone release (1), kidney tubules reabsorption of Na
+
(2).
The correct answer is c—
D.
Answer d is incorrect. The correct order begins with a drop in blood pressure recognized by the JGA (4), followed by the release of rennin (3), angiotensin II production (5), aldosterone release (1), kidney tubule reabsorption of Na
+
(2).

Challenge Questions
1. Indicate the areas of the nephron that the following hormones target, and describe when and how the hormones elicit their actions. a. Antidiuretic hormone b. Aldosterone c. Atrial natriuretic hormone
Answer
—
1a. Antidiuretic hormone (ADH) is produced in the hypothalamus and is secreted by the posterior pituitary. ADH targets the collecting duct of the nephron and stimulates the reabsorption of water from the urine by increasing the permeability of water in the walls of the duct. The primary stimulus for ADH secretion is an increase in the osmolarity of blood plasma, which occurs when a person is dehydrated or when a person eats salty foods. Osmoreceptors in the hypothalamus detect the increased osmolarity and stimulate the release of ADH.
1b. Aldosterone is produced and secreted by the adrenal cortex in response to a drop in blood Na
+
concentration. Aldosterone stimulates the distal convoluted tubules to reabsorb Na
+
, decreasing the excretion of Na
+
in the urine. The reabsorption of Na
+
is followed by Cl
–
and water, and so aldosterone has the net effect of retaining both salt and water. Aldosterone secretion however, is not stimulated by a decrease in blood osmolarity, but rather by a decrease in blood volume. A group of cells located at the base of the glomerulus, called the juxtaglomerular apparatus, detect drops in blood volume that then stimulates the renin-angiotensin-aldosterone system.
1c. Atrial natriuretic hormone (ANH) is produced and secreted by the right atrium of the heart, in response to an increase in blood volume. The secretion of ANH results in the reduction of aldosterone secretion. With the secretion of ANH, the distal convoluted tubules reduce the amount of Na
+
that is reabsorbed, and likewise reduces the amount of Cl
–
and water that is reabsorbed. The final result is the reduction in blood volume.
2. John’s doctor is concerned that John’s kidneys may not be functioning properly due to a circulatory condition. The doctor wants to determine if the blood volume that is flowing through the kidneys (called renal blood flow rate) is within normal range. Calculate what would be a “normal” renal blood flow rate based on the following information:
John weighs 90 kg. Assume a normal total blood volume is 80 mL/kg of body weight, and a normal heart pumps the total blood volume through the heart once per minute (cardiac output). Also assume that the normal renal blood flow rate is 21% of cardiac output.
Answer —Under normal conditions, John’s total blood volume would be 80 mL/kg of body weight or 90 x 80 = 7,200 mL or 7.2 L.
His cardiac output would be 7.2 L/min.

His normal renal blood flow rate would be 21% of cardiac output, or 7.2 L/min x
0.21 = 1.5 L/min.
If John’s kidneys are not affected by his circulatory condition, his renal blood flow rate should be about 1.5 L/min.
3. Why can an elephant in a zoo in a temperate climate go outside on a cold day while a smaller mammal like a mouse would stay inside?
Answer
—The ratio between surface area (measured in square area) and volume
(measured in units cubed) changes as dimensions increase. So a larger animal will have less surface area and therefore less opportunity to lose heat to the environment.
Conversely, small animals have greater surface area relative to their volume and will tend to lose heat too fast without adaptations like insulation and increased metabolic rate.
Large animals, especially in hot climates, have little insulation and may also use large or broad appendages to dissipate heat (ears, limbs). But in colder climates, the elephant’s relative lack of surface area could be an advantage.