Microorganisms Class 8th Science Notes

Microorganisms:

Microorganisms (microbes) are the very tiny living organisms which can not be seen normally. They are so small that we need to use microscope to see them.

Classification of Microorganisms

Microorganisms are broadly classified into four groups.These are

1. Bacteria
2. Protozoa
3. Fungus
4. Algae

One more microscopic entity virus is often misunderstood as a microorganism.However it can reproduce only when it enters in a host cell. The host cell for a virus can be a bacterium, plant or an animal cell.

Microorganisms, like other living things, have a role to play in our daily life.Some of them may be dangerous and even fatal but not all of them are so. Some Microorganisms are very useful and play an important role in our day to day life.Let us learn how are they dangerous and what are their benefits.

Harms caused by Microorganisms

Microorganisms may cause diseases in plants and animals (including humans).Bacteria may cause many diseases ranging from a mild infection to a very serious illness.Similarly Protozoa , algae and fangus may also cause many diseases.Some diseases caused by them are given in the table below.Viruses also cause very common to rare and serious diseases in human beings and other organisms.

Sr.No.	Name of the Pathogen	Host Organism	Diseases Caused
1	Bacteria	Humans	Cholera
2	Bacteria	Humans and cattle	Tuberculosis
3.	Bacteria	Humans	Pneumonia
4	Protozoa	Cattle	Theiliriosis
5	Fungi	Plants	Black Spot
6	Fungi	Human	Food Poisoning, Vomiting,Diahorrea
7	Virus	Humans	Influenza, Coughs, Fevers
8	Virus	Plants	Dry leaves, wheat mosiac diseases.

Microorganisms not only cause diseases in humans but they spoil our food, harm our crops etc.

PATHOGENS: The microorganisms which cause diseases are referred to as pathogens.

Now we have an idea that how Microorganisms can be harmful.Let us now see their benefits.

Benefits of Microorganisms

As we already know that all Microorganisms are not harmful to us. Some of them are highly useful for human beings. Let us see how do they benefit us.

1. Microorganisms decompose the remains of dead organisms and the faeces of animals.So in this way they clean up our surroundings.
2. Bacterium Lactobacillus changes the milk into curd.It is also helpful in digestion of milk and milk products.
3. Yeast is commercially important as it is used in baking industry to make cakes and bread.
4. Yeast can also be used in the production of alcohol.
5. Bacterium Rhizobium fixes atmospheric nitrogen to make it available for the use of plants.
6. Microbes can also be used in the pharmaceutical industry to manufacture antibiotics and vaccines.

Communicable Diseases

The diseases that can spread from one person to another through different media like air, food, water, physical contact etc are called communicable diseases. For example HIV AIDS, Covid 19, Influenza and Hepatitis B are communicable diseases because they can spread from one individual to another.

Vaccines:-

In order to prevent some diseases a weak or dead microorganism is administered into a healthy person so that the body can make antibodies against that particular type of microorganism and if that organism enters the body again in future the antibodies can recognize that organism and fight with it.

Antibiotics:-

Medicines which are used to stop the growth of pathogens or to kill them are called antibiotics.Few examples of antibiotics are streptomycin, azithromycin, tetracycline etc.