Microorganisms

A microorganism is an organism that is microscopic (usually too small to be seen with the human eye). Microorganisms are the smallest of the small and the simplest of the simple. They form the largest number of living organisms on the planet. There are trillions of microbes around the Earth.微生物是一切肉眼看不见的微小生物。它们的形体微小，构造简单，是地球上数量最多的生物。它们广泛分布在自然界中。

微生物的种类 Types of microorganisms

There are many types of microorganisms such as germs, viruses, fungi and protozoa.微生物有许多种类，例如细菌、病毒、真菌和原生动物。

 Microorganisms are part of our lives. Some are harmless and useful to humans. They have benefited the human race in many ways. However, there are also harmful microorganisms. These microbes can threaten our lives too. 微生物和人类的关系非常密切。有些对人类有益，是人类生活中不可缺少的良伴；有些却对人类有害，对人类生存构成威胁。