NCERT Class 4 Science: World of Microbes Complete Notes (For CBSE, ICSE, IAS, NET, NRA 2022)

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Key Notes –

1. We are surrounded by thousands of tiny organisms which can be seen only through a microscope. These are called microorganisms.

2. Microorganisms are present all around – in the air, soil, water, plants, and animals and even in humans.



4. Bacteria are one celled tiny organisms present everywhere around us. They reproduce very fast and can be double every half an hour if conditions are right.

5. Parasitic bacteria depend on living thing and saprophytic bacteria depend on decaying matter.


Useful and Harmful Bacteria

7. Viruses are smaller than Bacteria. They cause diseases like polio, measles, viral fever, common cold, HIV, dengue, etc.

8. Protozoa is also a single celled organism that lives in water. Protozoa causes diseases like malaria and dysentery.

9. Fungi are non-green plants.

  • Harmful Fungi
    • Disease like ringworm is caused by fungi.
    • They also cause rotting of fruits, vegetables
  • Useful Fungi
    • The fungus yeast makes breads and idles fluffy and spongy.
    • Yeast helps in fermentation
    • Some mushrooms are edible fungus
    • Penicillin a lifesaving medicine is made from fungi.

10. Algae are some green patches found in ponds and lakes. Blue green algae which helps in fixing atmospheric nitrogen to enrich soil fertility.


11. Some of the diseases can be protected through vaccination. It is a process though which intentionally weakened microbes are inserted in a healthy body so that the antibodies are produced and gain the capability to resist the disease further on.

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