What does respiration stand for in one word: breathing, energy, oxygen, cells or food?
Well, if you need a one word answer, the word "respiration" is taken from the word respire, which means "to breathe". Cellular respiration literally means "cell breathing", although the process is a little more complicated than that. All the words you have to choose from are involved in the process of cellular respiration, which is how animal cells get the energy they need to conduct their life processes. A molecule of glucose, delivered by the digestive system breaking down the food you eat, is oxidized by oxygen, delivered by the lungs. This chemical oxidation releases energy, which is stored in the form of ATP (adenosine triphosphate), and manufactures wastes in the form of carbon dioxide and water. The carbon dioxide is exhaled from the lungs, while the water is reclaimed into the circulatory system. So, as you can see, while we pick the one word "breathing" for the answer to your question, cellular respiration involves all the words present in your answer selection choices.
In one word, respiration actually stands for energy. Respiration does not have to involve oxygen because it can be anaerobic respiration(fermentation). However, the end result of this enzyme-- controlled chemical reaction, which occurs in a series of steps, is the production of the high energy compound known as adenosine triphosphate (ATP). This is the "energy currency" used by cells to carry out their life processes. Obviously the other terms--cells, food, oxygen and breathing are all part of aerobic respiration, however, the main idea of the words you have supplied is respiration.