Why does anaerobic respiration occurs after aerobic respiration an athlete's body?​

Explanation:

As the athlete works harder, their body uses more and more oxygen. Eventually, the body is not able to keep up with the the oxygen demand, thus it switches to anaerobic respiration temporarily. Anaerobic respiration does not use oxygen and thus is used after the body cannot supply oxygen quick enough.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.