Why do living things use enzymes instead of heat as a source of activation energy?

All living things need to eat and some do/do not use energy

animals such as pigs spider or man cannot do this since they are not a plant and cannot change heat into energy

Living things use enzymes instead of a heat source because they speed up chemical reactions as well as the metabolism in those living. Adding sufficient heat would harm or kill a living thing, also enzymes are far more efficient. A single enzyme can often carry out thousands of reactions per second. Living organisms use enzymes for activation energy because they speed up chemical reactions.