The cell is the basic structural, functional, and developmental unit of the body. The human body contains hundreds of trillions of cells, each of which is capable of performing the necessary functions of life.

CELL STRUCTURE

There is no typical cell that can be examined to determine the functions of the various parts. However, most cells have certain basic common components and it is, therefore, possible to visualize and describe a composite cell that combines the observed features of numerous cell types. Such a composite cell would be made up of the following components.

Cell Membrane

Each somatic (body) cell is surrounded by a semi permeable membrane that controls the exchange of nutrients and waste between the cell and its environment.

Nucleus

A cell usually contains a nucleus surrounded by some form of protoplasm and enclosed by a semi permeable membrane. The nucleus has been called the control center of the cell. One important known function of the nucleus is the transmission of hereditary traits. This is actually carried out by the chromosomes or chromatin material that is found in the nucleus of the cell. Chromosomes are made up of DNA (deoxyribonucleic acid), which has been called the “super molecule.” The cell nucleus also contains a thick fluid called karyoplasms in which are suspended small bodies known as nucleoli.

Cytoplasm

Cytoplasm is the fluid substance surrounding the nucleus and surrounded by the cell membrane. Suspended within the semi liquid cytoplasm are living bodies (organelles) and nonliving substances such as proteins, fat droplets, pigments, and various crystals. Within the cytoplasm are found the following:

Centrosome. Usually located near the cell nucleus and believed to initiate cell division.

Mitochondria. Minute fluid bodies in which numerous chemical reactions occur from which the cell’s energy is derived. Mitochondria are sometimes called the power plants of the cells.

Lysosomes. Digestive centers which break down large molecules and which aid in destroying the cell at the end of its useful life.

Ribosomes. Believed to synthesize protein.

The endoplasmic reticulum. A network of internal membranes which form a series of small canals through the cytoplasm for the purpose of transporting substances from the cell membrane to the nuclear membrane.

Golgi body (or com la ex). A series of smooth membranes continuous with the endoplasmic reticulum which is believed to have something to do with regulating the movement of fluids in the cell.

Fibrils. Thin, protoplasmic threads in the cytoplasm that probably give the cell structural support.

CELL DIVISION

The two basic types of human cells, somatic cells and sex cells, mature and increase in number through processes known as mitosis and meiosis, respectively.

Mitosis

Mitosis is the form of cell division that occurs in higher forms of animal life, including man. This form of cell division consists of four phases (prophase, metaphase, anaphase, and telophase) during which the chromatin material in the nucleus undergoes various changes in arrangement, leading to the ultimate division of the cell. The result of mitosis of a somatic cell is two daughter cells, each of which possesses the same number of chromosomes as the parent cell. In humans, each somatic cell contains 23 pairs, or 46 chromosomes.

Meiosis

Sex cells mature and propagate by a different process than somatic cells. This process is called meiosis. In meiosis, the series of nuclear changes within the sex cell results in the production of new cells with half the number of chromosomes present in the original sex cell. Meiosis occurs in both female and male sex cells, resulting in the formation of ova and spermatozoa, respectively. The union of a mature spermatazoa and a mature ovum results in the formation of a new individual. As a result of meiosis, the chromosome number remains constant from one generation to the next. For this reason, meiosis is sometimes called reduction division.

Share This