The body of an animal may compare to some machine such as a locomotive. In fact, the body of an animal itself is a machine, which is composed of many parts. Each part plays a special role, with special structure supporting it. All of the parts rely on and cooperate with each other, in order to fulfill the operation(fulfill和operation搭配有点怪) of the machine. A locomotive has to be added (with) fuel, such as coal, firewood, or other flammable substance, consuming which(分词跟这样的clause好像不常见，见到过分词+what从句，不太确定你这个对不对，可以改为consumption of which或者另起一句) may provide motion or energy for the machine. The body of an animal also need（s） fuel supplementation being called food, which may provide（provides） energy to the animal. In order to ignite the flammable substance and oxidize the food in the animal body, oxygen is essential. （病句，还是我上次跟你说的人称问题， 可以说：Oxygen is essential in doing something，也可以说Oxygen is needed to do something. 我觉得如果非要用 In order to…, 主语得是人， in order to ignite the flammable substance, we need to add oxygen. ） The locomotive is composed of special parts: the hearth to accept（accept用的有点怪，accept很少主语是物，因为有主观性，接受/拒绝) and ignite the flammable substance, the pipe to transport steam, the wheel to make the locomotive move on（怪，这里用从句可能好点， the wheels that enable the locomotive to move）, and the chimney to exhaust gas. While（while用得不对，我觉得while如果在句首，后面的句子常常表转折。可以换成Similarly，the animal body…） the animal body is also composed of different parts: gastrointestinal tract to ingest and absorb food, the emunctory organ to evacuate waste, the arteries and veins to transport oxygen and store nutriment, and the legs and wings to move on(和前面一样，用从句好点儿。去掉on好像好一点儿，就像说：The animal body needs the legs and wings to move around. ).
