John is working near a hot surface when he accidentally leans up against it. almost instantly and without thinking, he reacts by pulling his hands away from the surface without getting burned. this is because his system responds fastest to changes in environmental stimuli.

nervous

Explanation:

The nervous system responds fastest to changes in environment stimuli.

it depends on how much it could carry.

the sun creates it's own light, also gives light and life to bunch of stuff like plants,animals,humans etc.photosyntesis is the process of making food which needs sun,water,nutrients etc.