特点英文

特点英文
特点英文

特点英文
Evolution
Single-celled microorganisms were the first forms of life to develop on earth,approximately 3–4 billion years ago.Further evolution was slow,and for about 3 billion years in the Precambrian eon,all organisms were microscopic.So,for most of the history of life on Earth the only form of life were microorganisms.Bacteria,algae and fungi have been identified in amber that is 220 million years old,which shows that the morphology of microorganisms have changed little since the triassic period.
Most microorganisms can reproduce rapidly and microbes such as bacteria can also freely exchange genes by conjugation,transformation and transduction between widely-divergent species.This horizontal gene transfer,coupled with a high mutation rate and many other means of genetic variation,allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses.This rapid evolution has led to the recent development of 'super-bugs' — pathogenic bacteria that are resistant to modern antibiotics.
Importance
Microorganisms are vital to humans and the environment,as they participate in the Earth's element cycles such as the carbon cycle and nitrogen cycle,as well as fulfilling other vital roles in virtually all ecosystems,such as recycling other organisms' dead remains and waste products through decomposition.Microbes also have an important place in most higher-order multicellular organisms as symbionts.Many blame the failure of Biosphere 2 on an improper balance of microbes.
Use in food
Microorganisms are used in brewing,baking and other food-making processes.
The lactobacillus / lactobacilli and yeasts in sourdough bread are especially useful.To make bread,one uses a small amount (20-25%) of "starter" dough which has the yeast culture,and mixes it with flour and water.Some of this resulting dough is then saved to be used as the starter for subsequent batches.The culture can be kept at room temperature and continue yielding bread for years as long as it remains supplied with new flour and water.This technique was often used when "on the trail" in the American Old West.
Microorganisms are also used to control the fermentation process in the production of cultured dairy products such as yogurt and cheese.The cultures also provide flavour and aroma,and to inhibit undesirable organisms.
Use in water treatment
Microbes are used in the biological treatment of sewage and industrial waste effluents.
Use in energy
Microbes are used in fermentation to produce ethanol.
Use in science
Microbes are also essential tools in biotechnology,biochemistry,genetics,and molecular biology.Microbes can be harnessed for uses such as creating steroids and treating skin diseases.Scientists are also considering using microbes for living fuel cells,and as a solution for pollution.
Use in warfare
In the Middle Ages,dead corpses were thrown over walls during sieges,this meant that any bacteria carrying the disease that killed the person/creature would multiply in the vicinity of the opposing side.