Microorganisms Friend and Foe Notes || Class 8 Chapter 2 Science ||
Chapter – 2,
Science
MICROORGANISMS:
FRIEND AND FOE
1. Microorganisms/microbes are very small which cannot be seen with
the help of eyes.
2. We use microscope or magnifying glass to see them.
3. E.g. fungus that grows on bread
Classification of Microorganisms
1. It is
classified into four major groups
2. Bacteria, fungi, protozoa and algae
3. Viruses are other kind of
microorganisms.
4. They are explained below –
Bacteria
1.
Bacteria are very
small, single celled micro-organisms which have cell walls but do not have an
organised nucleus & other structure
2. These are found everywhere like in air, soil, water, every
surface around us, on our bodies or inside our body.
3. Two common examples are Lactobacillus & Rhizobium
4.
Some are useful
& help in making foods (like curd (दही)) & some can cause disease like cholera (हैजा), typhoid (मियादी बुखार), tuberculosis (TB) & food Poisoning (पेट दर्द).
Protozoa
1.
It is a single celled
micro-organism.
3. Some common examples of protozoa are Amoeba, paramecium,
Plasmodium.
Algae
1.
It is a large group
of simple, plant like organisms.
2. They contain chlorophyll & produce food by photosynthesis
just like plants.
4.
Some are
unicellular & most of the algae are multicellular.
Fungi
1.
Fungi are a large
group of organisms which do not have chlorophyll & photosynthesis.
2. Some examples are Yeast, Moulds (such as bread mould,
penicillium), Mushrooms etc.
3. Some fungi look like plants but they cannot make their own food
like the plants.
4. They food on dead things like remains of dead plants &
animals
5.
Fungi need moist
& warm conditions to grow.
Viruses
1.
Viruses are the
smallest micro-organisms which can develop only inside the cells of the host
organisms (may be animals, plants)
2. Viruses can reproduce & multiply only inside the cells of
other organisms (such as animal cell, plant cell or organisms cell)
3. Thus, as long as viruses are outside the living cells, they
behave as non-living things.
4.
Diseases produced
by them are common cold, influenza (ज़ुकाम) (flu), measles (खसरा), polio, chickenpox & smallpox etc
Where do Microorganisms Live?
1.
Microorganisms may
be single-celled like
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