Microorganisms: Friends And Foe
NCERT SOLUTIONS FOR 8TH CLASS
J&K BOARD NCERT 8TH CLASS
1. Fill in the blanks.
(a) Microorganisms can be seen with the help of a ____________
(b) Blue green algae fix __________ directly from air and enhance fertility of the soil.
(c) Alcohol is produced with the help of __________
(d) Cholera is caused by_________
Solution:-
(a) Microscope
(b) Nitrogen
(c) Yeast
(d) Bacteria
2. Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen
(b) The following is an antibiotic
(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly
(d) The most common carrier of communicable diseases is
(i) ant (ii) housefly (iii) dragonfly (iv) spider
(e) The bread or idli dough rises because of
(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection
Solution:-
(a) (ii) alcohol
(b) (ii) streptomycin
(c) (i) female Anopheles mosquito
(d) (ii) housefly
(e) (iii) growth of yeast cells
(f) (iii) fermentation
Question 3.
Match the organisms in column A with their action in column B.
Column A | Column B |
i) Bacteria | a) Fixing Nitrogen |
ii) Rhizobium | b) Setting of curd |
iii) Lactobacillus | c) Baking of Bread |
iv) Yeast | d) Causing Malaria |
v) Protozoan | e) Causing Cholera |
vi) Virus | f) Causing AIDS |
g) Producing Antibodies |
Solution:
(i) (e) (ii) (a) (iii) (b) (iv) (c) (vi) (f)
Question 4.
Can microorganisms be seen with the naked eye? If not how can they be seen?
Solution :-
No, microorganisms are very small and can not be seen with a naked eye.They can only be seen through a microscope.
Question 5.
What are the major groups of microorganisms?
Solution:-
There are four major groups of microorganisms.They are
- Bacteria
- Protozoa
- Fungi, and
- Algae
Viruses are also microscopic.However they can reproduce only when they enter into a host cell.
Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Solution:-
Some nitrogen-fixing bacteria are Rhizobium, Rhodobacter and Clostradium.
Question 7.
Write 10 lines on the usefulness of microorganisms.
Solution:-
Microorganisms are useful in the following ways.
- Microorganisms clean the environment by decomposing dead organisms.
- Microorganisms can be used to produce antibiotics.
- Microorganisms are used to make vaccines against many diseases.
- Bacterium Lactobacillus is used to set curd.
- Bacteria are used to produce acetic acid.
- Microorganisms live in our intestines and help in digestion.
- Yeast is used in baking industry to make bread and cakes.
- Yeast is used to convert sugar into alcohol.
- Microorganisms are used to make cheese.
- Bacteria like Rhizobium fix atmospheric nitrogen into nitrogenous compounds and help plants to take up nitrogen.
Question 8.
Write a short paragraph on the harms caused by microorganisms.
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.Viruses also cause very common to rare and serious diseases in human beings and other organisms.
Question 9.
What are antibiotics? What precautions must be taken while taking antibiotics?
Solution:-
Antibiotics are medicines which are prepared from microorganisms.They stop the growth of disease causing microorganisms (pathogens).We should always complete a course of antibiotics as prescribed by physician and if we miss a dose , it must be taken immediately. Antibiotics should never be taken without the prescription of a doctor.