What is an endotherm? how do sweating, fur, and feathers affect the body temperatures of endotherms?

1. What is an endotherm?
Endotherm is an animal that keeps their temperature constant in a certain range. Keeping temperature is important because most enzyme has an optimal working range. By keeping the temperature at optimal range for the enzyme, the organism can do metabolism more efficient.

2. how do sweating, fur, and feathers affect the body temperatures of endotherms?
The environments temperature should influence the temperature of an organism that lives within it. Endotherms need to control their temperature, so they have some mechanism to increase/decrease the body temperature. or to insulate themselves from the environment.
Sweating help decreasing temperature makes the organism can withstand hot environment. Fur and feather will insulate the body, makes the organism more resistant to cold.