All living things, including plants, must ___________ in order to obtain the energy they need to __________ and repair tissue. Unlike plants, animals are unable to make their own food. Therefore, they must _____________ around in search of food, water and shelter for survival. In living things, the food is converted to energy in the cells by the process of ___________, which usually occurs in the presence of oxygen. Chemical processes like these, which occur in cells, usually result in the formation of toxic byproducts, which must be eliminated, from the body by the process of __________. Living things will eventually die; therefore, they must _________ in order to prevent their species becoming extinct.