Question

Salmon are masters of osmoregulation. They are able to control both body fluids and ions during the transition from fresh water to salt water and back again. Young salmon, called smolt, are born of eggs hatched in freshwater and must prepare for life in the salty ocean. The young salmon will soon be bathed in ocean water that is about three times as concentrated as its body fluids, meaning that it will tend to lose water to its surroundings all of the time. All BUT ONE adaptation helps the salmon survive the change from fresh water to salt water.

A The salmon start drinking a lot of water.The salmon start drinking a lot of water.
B The salmon excrete a lot of very dilute urine.The salmon excrete a lot of very dilute urine.
C The kidneys drop their urine production.The kidneys drop their urine production.
D The gills actively pump Na+ and Cl− ions out into the water.

Answer 1

A, B, and C are adaptations that help the salmon survive the change from fresh water to salt water. The salmon start drinking a lot of water to compensate for the water loss to its surroundings, and excrete a lot of very dilute urine to get rid of excess water and retain essential salts. The kidneys drop their urine production to conserve body fluids.

D is not an adaptation that helps the salmon survive the change from fresh water to salt water. Instead, it would cause the salmon to lose more ions and water to its surroundings, exacerbating the osmotic stress. Therefore, the correct answer is D.

Step-by-step explanation: