Cells, the building blocks of the body, have specialized organelles that carry out specific functions.
Most organelles are dispersed within the cytoplasm which is the jellylike material of the cell.
Most cells are very small and must be studied with microscope. The microscope is one of the biologist's most important tools for studying the internal structure of cells. Most cell structures were first identified with an ordinary light microscope, which uses visible light as the source of illumination. The development of the electron microscope, which came into widespread use in the 1950s, enabled researches to study the fine detail (ultra structure) of cells and their parts. The electron microscope uses an electron beam of energized electrons. Photographs taken with the light microscope are referred to as light micrographs (LMs) and photographs taken with the electron microscope are referred to as electron micrographs (EMs) .
The size and shape of the cell are related to the specific functions it must perform. For example, sperm cells are tiny cells with long, whiplike tails (called flagella) . The tail is used to move towards the ovum or egg. The ovum is one of the largest cells in the human body. Epithelial cells which look like little building blocks cover body surfaces and line body cavities. Muscle cells are elongated and specialized for contraction. Nerve cells have long extensions that permit them to transmit messages over long distances within the body. Lymphocytes, a type of white blood cells, change their shape as they move through the tissues of the body, destroying invading bacteria.
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