Cell and Cell Structure

Introduction

     The cells that make up our body are so small that you would fit over 200 of them on the full stop at the end of this sentence.

Cell - A Unit of Life

     All living organisms, whether plants or animals, are made up of microscopic units called cells. The cell occupies the same central position in biology as the atom in the physical sciences.

Structure of Cell

     Cells vary in shape and size. They may be oval, spherical, rectangular, polygonal, spindle shaped, star shaped, rod-shaped or totally irregular like the nerve cell.

Cell Organelles

     These organelles are found in the liver and kidney cells. They are small, membrane-bound sacs, and contain powerful oxidative enzymes. Their chief function is to remove toxic substances.

Activities using the Microscope

     Peel off the thin epidermis (skin) in the inner layer of an onion. Neatly spread it in the centre of a glass slide on a drop of water. Add a drop of Iodine solution and gently place the cover slip.

Prokaryotic and Eukaryotic Cells

     The main difference between these two cell types is that Prokaryotic cells do not have a nuclear membrane. The nuclear material consists of a single chromosome and lies in the cytoplasm. The nuclear region in the cytoplasm is called nucleoid. Membrane-bound organelles are absent. Prokaryotic cells are found in bacteria and cynobacteria (blue-green algae).

Types of Cell Division

     Cell division is a method by which new cells are originated from pre-existing cells. The formation of daughter amoebae in amoeba, the development of sex cells and the growth of a young animal or plant into an adult, all involve cell multiplication. In order to multiply in number, cells undergo cell division: one divides into two, two into four, four into eight and so on.

Mitosis

     This type of cell division occurs in the somatic (body) cells. Here a diploid (2n) parent cell gives rise to two diploid (2n) daughter cells.

Meiosis

     This type of cell division occurs in reproductive cells (gametes). The male gamete is known as the sperm in animals and the female gamete is known as the ovum (egg). These gametes, after they are formed, have no future unless they unite to form a zygote, which then grows into an adult organism.