If you could measure the resting metabolic rate of the following animals, which would most likely have the lowest mass-specific (or relative) metabolic rate?

A. 100 Kg Horse

B. 100 Kg Shark

C. 10 g Mouse

D. 10 g Fish

The horse and mouse are endotherms among them rat will have high mass-specific metabolic rate.

The shark and fish are endotherms among them fish will have high mass-specific metabolic rate.

Explanation:

The endotherm (heat requires in them to maintain internal temperature of the body) organism have high metabolic rates to maintain homeostasis, this requires the large amount of energy. Smaller animals have the greater surface area to volume ratio, hence more heat loss and higher metabolism. In larger animals body volume increases, surface area increase is also very slow, hence less heat loss and lower Metabolic rate. Smaller animals exchange oxygen to tissues at a high rate.

Same goes with ectotherms the larger the animal the smaller is the metabolic rate. During winters their activity slows down as they cannot adjust with the temperature of the surrounding.

However metabolic rates of ectotherm and endotherm cannot be compared.