What organ system generates the heat needed by warm-blooded animals such as humans?

There are eleven major organ systems are present in human and animals. The organ system that generates the heat needed by warm-blooded animals such as humans is the muscular system. Aside from generating heat, the muscular system facilitates movement and locomotion. It produces body movements, maintains posture, and supports the body. Heat is generated thru muscle contractions and as much as 70% of the body heat is produced in the muscle tissue. 

the dark variety, as they are not visible on the dark tree barks

explanation:

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.