Cell

A cell is the smallest piece of living matter. Cells are like tiny `bricks’ which make up the bodies of plants and animals in the same way that a house is built of bricks. Most cells can only be seen under only a single cell. But the human body has billions of cells.

Each cell is made up of a central core called a nucleus and an outer pert containing a watery substance called the cytoplasm, in which food for the cell is stored. In a complicated animal, such as we are different cells have different jobs to do and so vary in appearance, shape and color. But all cells are basically made in the same way.

Virus

Virus is very small living things that cause disease in plants and animals. They can be only seen with a very powerful electron microscope when magnified 10,000 times. Unlike bacteria, virus (with a few exceptions) can not be destroyed by antibiotics.

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A Dutch botanist named Martinus Benjerinck realized that many diseases which could not be attributed to any bacteria are caused by some organism much smaller than bacteria. He named it `Virus’ meaning `poison’ in Latin.

By itself a virus is a lifeless particle but life it enters a living cell (of a plant or animal or man) it comes alive and can multiply it- self rapidly. The new viruses produced are released from the cell and become lifeless but come to life ah=gain upon entering another cell. When a virus reproduces, it changes the chemical composition of the cell it has invaded. The changes may destroy the cell and in many cells are destroyed in this way, disease results.

There are more than50 diseases including the common cold, chicken-pox, measles, polio and AIDS that are known to be caused by virus.

Yeast

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Yeast is plant which is also a kind of fungus. The whole plant consists of just one cell. It is so tiny that you can not see it with out a microscope. In the production of beer, wine and cider it converts sugar into alcohol. The process is called fermentation. In baking it release carbon dioxide from the dough, thus causing the bread to rise. Yeast also a valuable source of vitamin B.