The Cell

The living things around us - plants and animals which inhabit every part of the world – differ from non-living things because they take in food, they grow, and reproduce their kind.

Animals and plants have several other activities which distinguish them from non-living things. The study of plants and animals is a branch of science called biology.

If we examine a very thin piece of a plant under a microscope, we shall see that it has a honeycomb structure; it is divided into a great many small compartments called cells. Animal tissue, like plant tissue is made up of cells and in large organisms the number of cells runs into many millions. In such organisms there are many types of cells; they differ in function and also in shape and size. Each cell is surrounded by a cell wall or membrane, as it is generally called.

The cell walls of plants are formed of a substance called cellulose, which gives strength to the plant. Within the cell is a thick jelly-like substance called protoplasm, which consists of a mixture of chemical compounds together with a large proportion of water. The protoplasm is colourless and similar in appearance to the uncooked white of an egg. The protoplasm consists of cytoplasm and nucleus. The nucleus is a spherical or oval body within the cytoplasm. The nucleus plays an extremely important part in the life of the cell.

Everything we do, we do with our cells. An amoeba does everything – eats, grows, moves with just one cell. In a complicated creature like man, different cells do different things.

Stomach cells help digest your food, blood cells carry oxygen to different parts of the body, muscle cells help you move around, and so on. We say that all these different kinds of cells are specialized to do their particular jobs. But, of course, man is not really just a bunch of cells put together.

A bunch of muscle cells will not get along very well all by.themselves. It is the same with a bunch of digestive cells or a bunch of nerve cells. What you are and what you do, are really the result of all your various kinds of cells working together.

The same kinds of cells knitted together make tissue. Different tissues organized together make up organs. They in turn are organized into the systems such as the digestive system, that make our bodies work.

Date: 2015-12-13; view: 404; Нарушение авторских прав