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.
Metabolic rate is the rate of metabolism, the amount of energy used by an animal per unit of time. Basal metabolic rate (BMR) is the amount of energy used daily by animals at rest.
