Microscopic life
Translate the text “Microscopic life” into Russian, find the proper equivalents for the words given in bold type. Correct your translation after follow-up activities.
The most abundant forms of life are very small and can only be observed with a microscope. They are found in huge numbers in every habitat on earth. Many live in or on other larger living things. Many forms of micro-organism are carried in the air. Operating theatres, and some factories, use complex filters to keep micro-organisms out.
Bacteria
By far the most common of the micro-organisms are bacteria. They have a simple structure, and, under favourable conditions, can multiply at a very rapid rate. However, they have very special requirements. The size of bacterial colonies is controlled by the availability of food, a suitable temperature and other essential environmental factors. There are many thousands of different bacteria, but they are all made of just one cell. Aerobic bacteria need oxygen to survive; anaerobic bacteria are poisoned by it. Some bacteria are autotropic, which means they can make food for themselves from sunlight or chemicals. Others are heterotropic, which means they survive by feeding off organic matter. Most bacteria cannot move very far by themselves, so most heterotropic bacteria find a host to live on. Sometimes they get on well with their hosts and the relationship is good for both bacteria and host. This is called symbiotic relationship. There are bacteria in cows’ stomachs, for instance, which help break grass into more digestable lumps. Or the bacteria may simply live harmlessly on the host. The bacterium Escherichia coli or E. coli lives quite harmlessly in your intestine. This is called commensal relationship. But some bacteria are parasites that live inside the host’s body, and may damage the host by releasing poisonous chemicals called toxins. A bacterium that causes disease is called pathogen. Moreover, bacteria that are commensal in one place can be pathogenic in another. E.coli, for example, can cause disease if it gets into your urinary tract. Although bacteria can cause disease, many are useful. Some break down organic matter, releasing the nutrients to the soil. Some help ferment alcohol for drinks or are used in the cheese-making process. Some help in genetic engineering. Most bacteria multiply simply by splitting again and again. Sometimes, bacteria can survive for thousands of years in adverse conditions by creating spores.
Bacteria shape
Every bacterium has a rigid cell wall around a soft membrane holding a jelly-like protoplasm and the strands of DNA. Some also have flagellum (tail-like structure) to drive them along. Bacteria are often classified according to their shape. Cocci are round, bacilli are rod-shaped, vibrios are curved ans spirilla are spiral. Cocci that live in pairs are called diplococci, clusters are staphylococci and chains are streptococci.
Viruses
Viruses are the simplest of all forms of life, but they are so small (100 millionth of a millimeter long) that you can see them only under a powerful electron microscope. Unlike bacteria, viruses are entirely parasitic and cannot multiply outside a host. Indeed, outside a host cell, they are virtually lifeless. When a virus enters a host cell, it takes over the host’s chemical energy and protein-making ability in order to multiply itself. After the virus multiplies, the new viruses burst out of the cell, often leaving it dissolved.
The stages of this process:
Virus approaches the host cell.
Virus sticks to the surface of host cell and injects its DNA (genetic material).
The virus DNA replicates inside the host cell.
New viruses are formed inside the cell.
The cell bursts and the viruses spread out.