Ricky Pompilii, age 11, of Chester, Penna.,for the question:
What are living cells? ,
Put a penny on your hand and draw a pencil line around it. Remove the penny and look at the smooth skin inside the circle. A microscope would show that piece of skin to be made up of about two million living cells. The body of a grown person may contain a million, billion cells. Most of them are living and even the non living hair, nails and tooth enamel were made by living cells.
Every plant and every animal is composed of these busy little units of life. Most, but not ail, living cells are too small for our eyes to see. The yolk of a bird's egg is a single cell. The yolk of an ostrich egg is a single cell three inches wide. Certain nerve cells in the body may be six feet long= though these branches are finer than the finest spider web.
The simplest living things are but one single cell. The amoeba and his relatives are one celled animals. It may take 2500 of these litt.a.:: fellows to measure one inch. The bacteria, yeasts and algae are single¬celled plants. Even these tiny forms of life show differences between the plant and animal world.
The amoeba has features which appear throughout the animal world. It is clothed in a cell wall of soft, fine membrane or skin. This membrane lets ire liquids which may be useful to the amoeba and keeps out many things that are harmful. The veils in your hand are also soft. You can pinch them and they spring back into position. They have thin elastic walls which let in nourishing liquids and give out waste materials.
A bacterium is clothed in a cell wall of rather stiff material. The cells which make up a woody tree are encased in a stiff material called cellulose. Under the microscope, these plant cells look like tightly packed little boxes.
Though plant cell walls let certain liquids in and out, they are not pliable. If you pinch a plant or a leaf, its cells will not spring back into position like the elastic cells in your hand.
A one celled plant must be able to feed itself, digest its food aid multiply. It must do everything for itself. But no cell in your body could exist by itself. It is part of a vast hive of cells all living and working together. Like a city of busy peoples some cells specialize in one task and some in another. The cells are different in shape, depending upon the work they have to do.
Altogether, your body has about 50 different types of living cells. A brain cell may be a ragged shape with many fine branches. A muscle cell is often long and thin, tapered at each end. Some of the busiest cells are the little red corpuscles which float in the blood