Oxygenated blood returns to the left atrium through which of the following?

A. The medulla oblongata, located in the brainstem, is directly responsible for controlling the rate and depth of breathing. It detects changes in blood levels of CO2 and adjusts respiratory activity accordingly.

B. The hypothalamus regulates various autonomic functions, including body temperature, hunger, and thirst, but it is not directly involved in the control of respiration.

C. The midbrain is involved in functions such as vision, hearing, and motor control, but it does not directly control respiration.

D. The cerebellum is responsible for coordinating movement and balance, but it does not regulate respiratory control.

A. Oogenesis is the process of egg cell (ovum) formation in females and is responsible for producing gametes, not somatic cells.

B. Spermatogenesis is the process of sperm cell formation in males, also producing gametes, not somatic cells.

C. Mitosis is the process that produces somatic cells. It is a type of cell division that results in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell. Somatic cells are all body cells except for gametes.

D. Meiosis is the process that forms gametes (sperm and eggs), reducing the chromosome number by half to ensure sexual reproduction results in a normal chromosome count. It does not form somatic cells.