Notes prepared by Subhankar Karmakar
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Micro-organisms: some of them are bad, but some of them are good too.
Those organisms which are too small to be seen without a microscope are called micro-organisms. Some of the microorganisms are useful to us, but some of the micro-organisms are harmful to us.
Good micro-organisms:
For example, the microorganisms by certain bacteria help in making food products such as curd and cheese. Microorganisms are are also useful in making bread, cakes, pastries, alcohol, acetic acid or vinegar and medicines called antibiotics.
Bad Micro-organisms;
On the other hand, the microorganisms like certain bacteria and fungi make our food rotten. The Microorganisms also caused diseases in humans, other animals and plants. The diseases like common cold, malaria, skin infections, typhoid, tuberculosis, tetanus, cholera, measles, chicken pox, smallpox, AIDS and of course covid-19 are all caused by the action of various types microorganisms.
Major groups of microorganisms:
Microorganisms are classified into 5 major groups. This groups are:
1. Bacteria
2. Viruses
3. Protozoa
4. Fungi
5. Algae
Cellular structure of microorganisms:
Some microorganisms are unicellular or single celled where as many microorganisms are multicellular or multi celled.
1. Bacteria:
Bacteria are very small, single celled microorganisms which have cell walls but do not have an organised nucleus and other structures. They come in various shapes like spherical bacteria, rod shaped bacteria, and spiral bacteria.
Example: Beneficial bacteria:
Lactobacillus bacteria, which are useful for making foods like curd and Rhizobium bacteria which help in nitrogen fixation and decomposition of organic waste matter.
Harmful bacteria: Diseases like cholera, typhoid, tuberculosis or TB, diphtheria, whooping cough and food poisoning all are caused by actions of bacteria.
2. Viruses:
Viruses are the smallest microorganisms which can develop only inside the cells of the host organisms. They are neither alive nor dead. They are not exactly living things.
Viruses can reproduce and multiply only inside the cells of other organisms like animal cells plant cells or bacteria cells.
Viruses are the agents of disease. The human diseases such as common cold, influenza, measles, polio, chicken pox, HIV, smallpox and covid-19 are all caused by viruses.
3. Protozoa:
Protozoa are a group of single celled microorganisms which are classified as animals.
They are found in lakes, ponds, dirty water drains, sea water and damp soil.
Some common examples of protozoa are:
Paramecium, Entamoeba and Plasmodium.
Protozoa can be parasites also.
Diseases caused by protozoa:
• Entamoeba is a protozoan which causes a disease known as amoebic dysentery.
• Plasmodium is a protozoan which causes a disease called malaria. Plasmodium is also known as Malarial Parasite.
4. Algae:
Algae is a large group of simple plant like organisms. Like plants, they contain chlorophyll and produce food by photosynthesis.
Example: Chlamydomonas, Spirogyra, blue green algae, Diatoms are example of algae.
Blue green algae have the ability to fix nitrogen gas of atmosphere.
5. Fungi:
Fungi are a large group of organisms which do not have chlorophyll and do not photosynthesize.
Some examples of fungi are: Yeast, Moulds like penicillium and aspergillus, mushrooms, toadstools, puffballs.
All fungi are made up of fine threads called hyphae except Yeast.
Some of the human diseases caused by fungi are ringworm and athlete's foot.
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