Question

Which is an example of a response to a stimulus?

A.
the thick fur on an animal to protect it from cold weather

B.
an increasing heart rate when blood oxygen levels drop

C.
loss of water from the body as a result of excess sweating

D.
the presence of allergens in the air

Answer 1

B. Your heart is reacting to the stimulus of dropping oxygen levels.

A is not the answer because the thick fur is an adaptation that is always with the animal, so it's not a reaction to a stimulus. Nor will the fur suddenly become thicker if the animal is put in a giant freezer, and then thinner again when the animal is taken out. A reaction would be the fur fluffing up in cold weather (like getting goosebumps).

C is simply the result of an action.

D could *cause* a reaction, since allergens stimulate some sort of reaction in people. But allergens on their own are nothing.

Answer 2

thanks