What is the difference between a homeotherm and a poikilotherm?

A homeotherm is an organism which is able to survive only
when the internal body temperature is within a narrow range. If their body temperature
increases to higher levels or falls to lower levels the enzymes in the body are not able
to function and this leads to the death of the organism. Examples of homeotherms include
mammals, birds, etc.

Poikilotherms on the other hand can
survive with their internal body temperature varying over a wide range. They are able to
withstand a much larger variation in external temperature that affects the internal body
temperature. Examples of poikilotherms are fish and
reptiles.

This ability of homeotherms and poikilotherms
related to having to maintain a constant body temperature has its own advantages and
disadvantages. Some of which are that homeotherms need to use less resources as their
body enzymes are highly efficient due to the fact that they need to operate in a narrow
temperature range. This allows these organisms to grow larger and develop faster.
Poikilotherms on the other hand use up a lot of resources producing inefficient enzymes
which can operate over a wide temperature range.