Some animals have no gills when young but then develop gills that grow larger as the animal grows larger. What is the reason for this increase in gill size?
A) The young of these animals are much more active than the adult, which leads to a higher BMR (basal metabolic rate) and, therefore, a higher need for oxygen.
B) Relative to their volume, the young have more surface area across which they can transport all the oxygen they need.
C) The young have a higher basal metabolic rate.
D) Relative to their surface area, the young have more body volume in which they can store oxygen for long periods of time.

Question

Quizplus · Accepted Answer

Young animals have a higher surface area to volume ratio, which means they have a greater surface area across which they can transport all the oxygen they need. As the animal grows larger, its surface area to volume ratio decreases, making it more difficult to obtain enough oxygen through diffusion alone. Therefore, the animal develops gills that grow larger as it grows to help meet its increasing oxygen demands.

Some Animals Have No Gills When Young but Then Develop