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THE STUFF OF LIFE
In their attempts to solve the mysteries of life, scientists have given much attention to the jellylike living material of the cell. This substance is called protoplasm. They have studied it under high-powered microscopes; broken it down into its basic chemicals; treated it with dyes and electric currents; and dissected it with microscopic needles. Yet no one has succeeded in making any protoplasm. It is one of the most complicated of all substances. We have learned many facts about it, but there are still many secrets to be discovered. Scientific research goes on, because protoplasm is the key to a real understanding of life.
Under the microscope, protoplasm is an almost colourless substance. At times it is quite liquid, but it can easily change to a more solid jelly. All the living parts of cell, including the cell membrane, the cytoplasm and the nucleus are made of protoplasm. With a high-powered microscope we can see many small particles and bubbles floating in the jelly. These are often in rapid motion.
The chemical nature of protoplasm is not exactly known. Unfortunately, when chemists begin to analyze it, it usually dies. This brings about changes in the material they are studying. We know that protoplasm is usually more than 75 per cent water. There are also salts and food materials such as sugars, fats and proteins. Four chemical elements make up 98 per cent of protoplasm. These are carbon, oxygen, hydrogen, and nitrogen. More than 15 other elements have been found. All of these are the common elements of which our earth is composed. There are no special elements that are found only in protoplasm. But such rare elements as strontium (Sr),rubidium (Rb), tin(Sn), nickel (Ni), gold (Au) and mercury (Hg) may enter into the composition of protoplasm as well. Where the soil is especially rich in certain minerals, the plants growing there may incorporate them, and they may find their way into the tissues or hard parts of animals that feed upon the plants. In some parts of the world gold is particularly abundant in the soil, and the hoofs, horns and hair of the deer living on the vegetation in these regions show relatively large accumulations of it. Radioactive elements in some regions are accumulated in the mosses and in vegetation of the region. These plants are the food for many animals, and analysis shows that these animals are also accumulating radioactive particles in their tissues. The food chain is extended to people living in these regions who feed upon these animals and in turn incorporate the particles in their own tissues. As a result their bodies contain a relatively high account of radioactive particles as compared with the population in general.
As a summary it should be noted that protoplasm is very a complicated mixture of many kinds of substances. These are in constant activity, carrying on the processes of life. When the activity stops, life comes to an end. "Biology and Human Progress" by L. Eisman, Ch. Tanzer.
Form synonyms of the following words:
research, substance, learn, to make up, to enter, certain, hard, enormous, to supply, rapid, occur, cause.
Date: 2015-04-23; view: 568; Нарушение авторских прав