Basic Description of the Human Cell

The chromosomes are threadlike assemblies that are extremely important because they contain the genes that transmit the hereditary information. Every species has a definite number of chromosomes. The human species has 23 pairs, one chromosome of each pair being contributed by each parent. Every cell has 23 pairs of chromosomes with the exception of the egg and the sperm, which have 23 chromosomes each. When fertilization occurs, the first cell of the new organism contains 23 pairs of chromosomes, equally contributed by each parent. 

Cells multiply by a dividing process called mitosis. Just before mitosis is to take place, each chromosome of the cell splits in two. Thus, each of the two new cells has exactly the same number of chromosomes as the parent cell. There are some human cells that do not divide, such as the blood cells and the nerve cells. The blood cells are regenerated by the blood-forming organs, primarily by the bone marrow. The nerve cells, when destroyed, are not supplied again. 

Radiation may damage the cell when it delivers extra energy to it because that energy may be used to destroy parts or functions of the cell. For example, as a result of irradiation, chromosomes or DNA molecules may break. The 

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