A potassium ion gradient is set up in insect Malpighian tubules through an active transport process. As a result, potassium concentration is higher in the lumen of the tubules than in hemolymph. How would the potassium gradient affect water movement?

A) Water would be forced out of the lumen of the Malpighian tubules through an osmotic gradient.

B) The potassium gradient would have no effect on water movement.

C) There would be a net movement of water into the lumen of the tubules.

D) Water would be conserved, forming a hypertonic solution in the Malpighian tubules.

Answer: C

Why are the renal artery and vein critical to the process of osmoregulation in vertebrates?

A) The kidneys require constant and abnormally high oxygen supply to function.

B) The renal artery delivers blood with nitrogenous waste to the kidney and the renal vein brings blood with less nitrogenous wastes away from the kidneys.

C) The kidneys require higher than normal levels of hormones.

D) The renal artery and vein are the main pathways regulating how much is produced by the kidneys.

Answer: B

The figure above shows a nephron. Filtration takes place in the structure labeled _____.

A) a

B) b

C) c

D) d

Answer: A

African lungfish, which are often found in small, stagnant pools of fresh water, produce urea as a nitrogenous waste. What is the advantage of this adaptation?

A) Urea takes less energy to synthesize than ammonia.

B) Small, stagnant pools do not provide enough water to dilute the toxic ammonia.

C) The highly toxic urea makes the pool uninhabitable to potential competitors.

D) Urea makes lungfish tissue hypoosmotic to the pool.

Answer: B

Which of the following most accurately describes selective permeability?

A) An input of energy is required for transport.

B) Lipid-soluble molecules pass through a membrane.

C) There must be a concentration gradient for molecules to pass through a membrane.

D) Only certain molecules can cross a cell membrane.

Answer: D

Through studies of insect Malpighian tubules, researchers found that K+ accumulated on the inner face of the tubule, against its concentration gradient. What can you infer about the mechanism of transport?

A) Potassium transport is a passive process.

B) Movement of potassium into the lumen of the Malpighian tubules is an energy-requiring process.

C) Potassium moves out of the tubules at a faster rate than it moves into the lumen of the tubules.

D) Sodium ions will follow potassium ions.

Answer: B