The smallest cell in the human body is a red blood cell. Red blood cells are about 6-8 micrometers in diameter, while the average human cell is about 10 micrometers in diameter. Red blood cells are responsible for carrying oxygen throughout the body. They do this by containing a protein called hemoglobin, which binds to oxygen in the lungs and releases it to the tissues.
Ovum, nerve cell, and sperm are all larger than red blood cells. Ovum are the female reproductive cells, and they are about 100 micrometers in diameter. Nerve cells are the cells that transmit information throughout the nervous system, and they are about 50 micrometers in diameter. Sperm are the male reproductive cells, and they are about 5 micrometers in diameter.
Red blood cells are the smallest cells in the human body because they need to be able to move through very small blood vessels. The smaller the cell, the easier it is for it to move through these vessels. Red blood cells are also very flexible, which allows them to change shape as they move through the blood vessels.