An organism, such as a fish or reptile, having a body temperature that varies with the temperature of its surroundings; an ectotherm.

Um, endotherms and ectotherms?

Right! All animals are considered either endotherms or ectotherms.

Therm-that means heat, and the main thing that distinguishes endotherms from ectotherms is the source of body heat.

And an ectotherm, ecto- meaning external, an ectotherm gets its body heat mainly from outside its own body, meaning from its environment, mostly from the sun's radiation.

I mean, the metabolic rate of an endotherm, say, a mouse, is at least six or seven times that of an ectotherm of a similar size like a frog or a lizard.

An ectotherm doesn't generate nearly as much heat internally.

It's by means of such behavior that an ectotherm like this lizard regulates its temperature.

But an ectotherm probably wouldn't survive in a place where the temperatures got too low, right?

Ectotherms can do that.

Student: Well, what about ectotherms, like frogs?

It's not what we endotherms do that keeps our temperatures within range, unlike ectotherms.