Your Cells
Have you ever looked through a microscope at a thin piece of leaf? If you have, you may have seen that the leaf is composed of small, bricklike parts called cells. Scientists have found that all living things are made of cells. You too are composed of cells many billions of them.
The cells of which you are built differ considerably from leaf cells. Your cells are generally smaller than those in a leaf. Unlike the leaf cells, yours are not great in color, since there is no chlorophyll in them. There are many different kinds of cells in your body.
Protoplasm
Cells are composed of a peculiar substance called protoplasm. Protoplasm is a jelly-like fluid, and resembles the white of an egg. It is about three fourths water. A great many different chemical compounds make up protoplasm.
The same chemical elements which are all around us make up the compounds in protoplasm. It contains some oxygen, hydrogen, carbon, and nitrogen. Some calcium, iron, sulfur, and magnesium are also found in it. Several other elements are found in it in small quantities. Protoplasm is a very unusual substance. But the chemicals in it are not strange or different from those you see around you every day. The carbon is like the carbon in a lump of coal. The oxygen is the same as the oxygen in the air. Calcium in the bones and teeth is similar to the calcium in the lime which the farmer spreads on his soil.
Protoplasm is a living material. It needs food to stay alive. Oxygen too must be brought to protoplasm continually. Both gas and liquid waste materials form in it; these wastes must be taken away. Later you will see how this is done.
Work of the Cells
You can think of your body as a city in which there are billions of inhabitants. Each of the inhabitants in this city is a cell. A great many things must be done in such a community. Damage done to parts of the body must be repaired. It temperature must be regulated. Food and oxygen must be circulated in it. Invading parasites which cause diseases must be fought off. A hundred other things must be done.
The different kinds of cells found the body are organized into cell groups. Each group the cells has some special job to do. Nerve cells, for example, are grouped together, forming nerve tissue. Muscle cells make up another kind of group. Each such group of similar cells is called a tissue. Many kinds of tissues make up the body, including bone tissue, muscle tissue, and skin tissue.
Tissues too come in groups. The heart, for example, is an organ composed of a group of muscle tissues. Bones are organs made up of a tissue in which there are cells containing much calcium and phosphorus. Can you name other organs of the body?
Finally each organ may be thought of as belonging to a system of organs. All the six hundred muscles of the body make up the muscle system. The heart, veins, arteries, and blood make up the circulatory system. The digestive system includes such organs as the tongue, stomach, and intestines. Can you name other systems of the body?
May increase your knowledge!
Thank you very much. . .
“Gerald S. Craig and John Urban”,
Professor of Sciences
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