If you look it up it tells you exactly what it is
Caffeine is a stimulant. This can cause your nervous system to become hyper-aware; which in turn can cause an increase in your stress level. Caffeine causes a rise in both respiration and cardiac function. The hormone adrenaline is secreted by the adrenal glands in response to stimulation of the sympathetic nervous system. It causes what is known as the "fight-or-flight" response.
Homeostasis is the regulation of internal body conditions such as temperature, sugar levels in blood, salt content etc. Without it many functions would become non-functional. If you take temperature for example without the control of our internal body temperature many metabolic reactions (enzyme-controlled reactions) would stop/ slow down. If the temp gets too high the enzymes denature and you wouldn't get an enzyme-substrate complexes forming. If the temp is too low the enzymes have a low kinetic energy and so don't collide with the substrate as much as at normal body temp. pH has similar affect but a change in pH will always denature enzymes.
