Bonnie Greens, age 14, of Rock Island, Ill., for her question:

JUST WHAT IS HEMOGLOBIN?

Hemoglobin is the pigment in blood that colors it zed. It is the most prevalent of the special blood pigments that transport oxygen. Hemoglobin is present in all but the least complex of animals.

Here's how you pronounce the word: bee muh gloh buhn.

Hemoglobin 1s part of the process by which blood carries required nutrients to the cells and transports their waste products to the excretory organs. Hemoglobin also carries oxygen from the lungs or gill, where blood is oxygenated, to body cells.

When saturated with oxygen, it is called oxyhemoglobin. After hemoglobin releases oxygen to the body tissues, it reverses its function and picks up carbon dioxide, the principle product of tissue respiration, for transport to the lungs, where it is expired. In this form, it is known as carboxyhemoglobin.

Hemoglobin is a protein that is contained entirely in the red blood cells, amounting to perhaps 35 percent of their weight. To combine properly with oxygen, the red blood cells must contain adequate hemoglobin. This, in turn, depends on the amount of iron in the body. An organism derives its store of iron by absorption from the gastrointestinal tract. The organism conserves and constantly reuses the supply of iron. A deficiency of hemoglobin caused by a lack of iron leads to anemia.

You'll be amazed to learn that hemoglobin carries more than 20 times its volume of oxygen. It combines so firmly with carbon monoxide that it can no longer combine with oxygen. This causes asphyxiation.

After a life of perhaps 120 days, red blood cells are destroyed in the spleen or, in the course of circulation, their hemoglobin is broken into its constituents, including iron, which enters new blood cells formed in the bone marrow.

When blood vessels rupture, as in an injury, the red cells are released and escape into tissue, where they are broken down. The hemoglobin is converted into bile pigments, the color of which is responsible for the appearance of bruises.

Alterations in the structure of hemoglobin can lead to life threatening illnesses. The most important of these conditions is sickle cell anemia, which involves a hereditary change in one of the amino acids that make up hemoglobin.

The thalassemias are a group of similar hereditary diseases causes by changes in the amino acid composition of hemoglobin.

Scientists have identified many different kinds of hemoglobin. A person inherits his hemoglobin type. Hemoglobin A ranks as the most common type.

Hemoglobin S, or sickle hemoglobin, is one abnormal type that can be inherited. Red blood cells that contain mostly hemoglobin S can become stiff and misshapen and plug blood vessels.