The Cell

All living things are composed of cells. Very simple organisms such as yeast¹ and bacteria consist of only one cell. They are one-celled or unicellular organisms. A large organism, such as a human being contains billions upon trillions of cells and is called a multicellular organism. A drop of blood, for instance, contains about forty billion cells. And there are thousands of drops of blood in the average man.

Despite its small size, each cell is a tiny drop of life. Some cells can exist independently, and do, as in the case of bacteria. Human cells however, have lost that ability. They depend on one another and specialise in one function or another. Some cells specialise in photosynthesis, some in digestion, some in excretion and some in reproduction.

Groups of cells of a similar shape, size and function form a tissue. When tissues of different types are grouped together for a common function they form an organ. Groups of cells, taken all together, are more advanced than single cells, even if the latter² are more independent. The living matter inside a cell is called protoplasm. The protoplasm is divided into parts. Near the center of the cell is a part, which is denser and thicker than the rest of the cell. It is the nucleus. The rest of the cell is cytoplasm.

Like any other living things, cells grow and multiply. Most cells multiply.by dividing down the middle. Then there are two cells where only one existed a moment before. The cell nucleus is in charge of seeing that cell division takes place properly. The cytoplasm takes care of the day-by-day life of the cell. Cells in different parts of the body vary in their shape according to the work they must do. Fat cells are just tiny blobs of fat surrounded by a thin layer of protoplasm. The red cells of the blood are little disks that contain a protein called haemoglo­bin, which carries oxygen to all other cells of the body. Red blood cells are so simple, they don't even have a nucleus and so cannot grow or di­vide.

Nerve cells have irregular shapes with long thread-like fibers sticking out⁵ of them. Impulses and sensations travel along those fibers. Muscle cells are long and thin. They can contract into short, thick cells when­ever necessary.

Some cells are so specialised that they have abandoned almost everything but⁶ their main function. They have even lost the ability to multiply. A baby is born with all the brain cells, for instance, that it will ever have. Still other cells are always growing. The cells of the skin grow and divide throughout life.

Notes

1. yeast [ji:st] – дрожжи

2. the latter – nocледние

3. by dividing – путем деления

4. is in charge of seeing – зд. отвечают за

5. sticking out – выступающий

6. but – кроме