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BIG ENCYCLOPEDIA FOR CHILDREN AND ADULTS
Can the virus be seen? Detailed answer
Directory / Big encyclopedia. Questions for quiz and self-education Did you know? Can the virus be seen? A virus is a microscopic organism that causes disease. It cannot be detected with an ordinary microscope. But this does not mean that science does not have the opportunity to study the structure of the virus. Today there are ultramicroscopes that make it possible to see microorganisms. Science is able to determine the size and types of viruses using an electron microscope. The electron microscope uses the glow of electrons instead of light rays. The electrons passing through the sample are observed and recorded on a photographic plate, on which the image appears. Therefore, it is possible to increase objects up to 100 thousand times. Using an electron microscope, it was possible to find out that the size of viruses ranges from 300 to 10 millimicrons. What is a millimicron? It's 1/1000 of a micron. A micron is 0,00001 millimeters. No one knows for sure what viruses are. Some scientists think they are close relatives of bacteria. Other researchers believe that viruses are similar to elementary particles close to genes. Still others believe that viruses are in the middle between living and non-living matter. We know that viruses can only grow and multiply in living tissue. This means that they cannot be cultivated outside of living matter, and this makes it difficult to study the properties of their growth. Therefore, they are classified according to their ability to infect living cells and according to the reaction that they cause in the body of animals or humans. Do viruses produce poisons and toxins? It is now recognized that they produce toxins, but the toxins and parts of the viruses cannot be isolated. And we still don't know how these toxins cause disease, if they do! Author: Likum A.
When was metal first used? About 6000 years ago, man lived in the Stone Age. It is named so because the main part of the tools of labor and hunting was made of stone. Man has not yet learned to make them out of metal. Most likely, the first metals that man began to use were copper and gold. The reason is that these metals in nature existed both in pure form and as part of the ore. A man found nuggets of copper and gold and could give them various shapes without melting. We cannot say exactly when man discovered these metals, but it is known that copper began to be used at the turn of the fifth millennium BC. Shortly before the onset of the fourth millennium BC, gold was also used. By the third millennium BC, man had already learned a lot in working with metal. By this time, silver and lead had also been discovered, but nevertheless, in most cases, copper was the most commonly used metal due to its strength and prevalence. First, a person learned to forge useful things from metal - dishes, tools and weapons. In the process of forging metal, he discovered the process of hardening (first, the metal is heated to a soft and viscous state, and then quickly cooled), melting, casting and smelting. He also learned how to get copper from ore, which was more abundant than nuggets. Later, a man discovered tin and learned to mix it with copper - a harder bronze was obtained. From about 3500 to 1200 BC, bronze was the most important material for making tools and weapons. This period is called the Bronze Age. Man learned about the existence of iron by finding meteorites long before he discovered how to smelt it from ore. By 1200 BC, man had learned to work iron, and his skills were passed down from generation to generation. Iron has largely replaced bronze. This was the beginning of the Iron Age. By the time of the rise of the Roman Empire, seven metals were known to man: gold, copper, silver, lead, tin, iron, and mercury.
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