Class 8, Science, Chapter-2, Lecture-1, Microorganism (Notes)
MICROORGANISMS:
The living organisms which cannot be seen with naked eyes are termed as microorganisms or microbes.
- the oldest form of life on earth are microbes.
Microbes are also called Micro-organisms.
Reason:
Micro means very Small.
The size of these organisms is very small and cannot be seen with naked eye.
Classification
- Bacteria
- Fungi
- Protozoa
- Algae
- Virus
Characteristics of Microorganisms:
- Bacteria:
- unicellular micro-organisms
- have cell walls
- does not have organized nucleus and other structures.
- are found in air, soil, water, on our bodies and inside our bodies.
- feed , move, respire and reproduce on their own.
- Diseases caused by Bacteria:
Cholera, Typhoid, Tuberculosis(TB), Diptheria, Whooping cough, Food poisoning etc.
- Viruses:
- are smallest microbes
- can develop only inside the cells of the host organisms (animal, plant or bacterium).
- are much smaller than bacteria
- do not show much characteristics of a living thing.
- Diseases caused by Viruses:
Common cold, Influenza (Flu), Measles, Polio, Chickenpox, Small pox, AIDS etc. - Diseases caused by virus cannot be treated with antibiotics.
- Viruses do not respire, feed, grow, excrete or move on their own.
They can only reproduce and multiply inside the cells of other organisms.
Viruses are agents of disease.
- Protozoa:
- are a group of single celled microorganisms which are classified as animals.
- found in ponds, lakes, dirty water drains, rains, sea water and damp soil.
- Many protozoa are parasites and cause diseases.
- Examples of Protozoa: Amoeba, Paramecium, Plasmodium and Entamoeba.
- Diseases caused by Protozoa:
Dysentery (Entamoeba), Malaria (Amoebic).
- Algae:
- is a large group of simple, plant like organisms but they do not have proper roots, stems or leaves.
- contain chlorophyll and produce food by photosynthesis.
- Examples of algae: Chlamydomonas, Spirogyra, Blue-green algae, Diatoms and Seaweeds.
- Some algae are unicellular- chlamydomonas and diatoms.
- Most algae are multicellular- blue-green algae and spirogyra.
- The blue-green algae act for nitrogen fixation in the atmosphere.
- Fungi:
- Fungi are a large group of organisms which do not have chlorophyll and do not photosynthesise.
- Examples: yeast, bread mould (rhizopus), penicillium and aspergillus, mushrooms, puffballs.
- All fungi except yeast are made up of fine threads called hyphae.
- Some fungi are parasites while most are saprophytes feeding on remains of dead plants and animals.
- Diseases caused by Fungi: Ringworm, Athelete’s foot.