Any dead animal or plant will rot quickly. Microorganisms are the main participants in causing decay. Rot will give off all kinds of unpleasant smells and naturally hinder satellites. However, don't underestimate this stench, which plays an irreplaceable role in the existence of the whole biological world and even the whole earth. We can imagine.
If there were no microorganisms to decompose animals when they died, thousands of corpses would accumulate every year for hundreds of millions of years. Is there room for humans on earth? Not to mention the plant growth of "rambling grass on the plain, coming and going with the seasons". There are trillions of tons of litter on the earth every year, which has accumulated for hundreds of millions of years. I'm afraid the ocean has been filled up and the land has been covered for several kilometers.
Among heterotrophic microorganisms, some get nutrition directly from dead organisms, and some get nutrition from some dead organisms. We call them saprophytic microorganisms. Most fungi and bacteria are saprophytic microorganisms. For example, the sewage discharged with the toilet sewer at ordinary times.
If it is not purified, a large number of microorganisms will be discharged into rivers, lakes and seas, and the nutrients in sewage will be used to multiply in large numbers, which will make the water body corrupt. Incomplete decaying compounds provide nutrients for microorganisms, which makes other microorganisms and even a variety of algae grow in large numbers. Finally, clear rivers and lakes may turn into smelly water.
If there is still a dead end in the environmental protection work in your city, I believe you can also see this situation. Of course, after a certain period of corruption, the organic matter flowing into the water body is decomposed, and the rivers and lakes will become clear. But this process is very slow, not to mention the continuous inflow of sewage, which increases the difficulty of clean water.
Microorganisms that grow in or out of organisms are called parasitic microorganisms, and they live a parasitic life like ascaris lumbricoides in human intestines. Parasitic microorganisms will deprive other organisms of nutrition and even rely on a certain part of their bodies for nutrition. Many fungi are parasitic on plants, which bring a lot of harm to plants.
Such as wheat rust, cucumber downy mildew, rice blast and so on. These parasitic microorganisms that cause plant diseases are no less harmful to human beings than parasites. They make crops grow poorly and reduce grain output. As a result, farmers lose a lot of hard-earned grain every year.
Bacteria enter people or animals through the mouth, skin or respiratory tract, and use the nutrition of people or animals to grow and reproduce. These bacteria are parasitic bacteria. If these bacteria produce toxins, it will make people sick, such as cholera, typhoid fever, pneumonia, etc., all caused by parasitic bacteria.
Diseases such as AIDS and colds are caused by viruses. Viruses are more specific parasitic microorganisms, because they cannot live without living cells, so they are called absolute parasitic microorganisms.
Some microorganisms, such as Fusarium, usually live in the soil and live on dead plants. But when crops are planted in this soil, under suitable conditions, they will enter the crops, absorb the nutrients of the crops, make the crops sick, and then they will become parasitic microorganisms.