Final answer:
Oxygen inhaled by the human body is used for cellular respiration to produce energy (ATP), while the carbon dioxide we exhale is a metabolic byproduct of this process.
Step-by-step explanation:
When we breathe, we inhale oxygen and exhale carbon dioxide. The oxygen we breathe in is used for cellular respiration, a metabolic process that occurs inside cells to produce energy. During cellular respiration, oxygen is used as a reactant and carbon dioxide is released as a waste product. On the other hand, carbon dioxide comes from various sources, including the waste product of metabolism, the decomposition of dead organisms and organic materials, and the burning of fossil fuels.
We inhale oxygen and exhale carbon dioxide because every cell in the body requires oxygen for cellular respiration, a process by which energy in the form of adenosine triphosphate (ATP) is produced. During cellular respiration, glucose is 'burned' in the presence of oxygen to release energy, water, and carbon dioxide. The oxygen we inhale is used primarily for oxidative phosphorylation, a part of the cellular respiration process that produces ATP. Carbon dioxide is a byproduct of this process and is expelled from the body when we exhale. Moreover, while photosynthesis requires carbon dioxide and releases oxygen, aerobic cellular respiration, occurring in our bodies, requires oxygen and produces carbon dioxide, contributing to the carbon cycle.
Therefore, the correct answer to the student's question is: a) Oxygen is used for cellular respiration; carbon dioxide is a byproduct of metabolism.