What do animals use to change what they eat (biomass) into energy?

Animals use oxygen to convert biomass into energy through a process known as cellular respiration. This biochemical process occurs in the cells of the body and involves taking in oxygen to help break down glucose (derived from biomass) into energy. During cellular respiration, cells utilize oxygen to oxidize glucose, leading to the production of adenosine triphosphate (ATP), which is the energy currency of the cell.

The process results in carbon dioxide and water as by-products, which are then expelled from the body. Oxygen is essential for aerobic respiration, which is the primary method by which most animals produce the energy they need for growth, reproduction, and other vital functions. This reliance on oxygen differentiates aerobic organisms from anaerobic ones, which do not need oxygen for energy production and rely on other biochemical pathways.

The other options, such as carbon dioxide, hydrogen, and nitrogen, play different roles in biological systems but are not directly involved in the primary process of converting biomass into usable energy through cellular respiration.