NCERT Solution - Micro-Organisms : Friend or Foe Notes | Study Science Class 8 - Class 8

Exercises

Q1. Fill in the blanks:

(a) Microorganisms can be seen with the help of a  microscope.

Microscope(b) Blue-green algae fix nitrogen directly from air to enhance the fertility of the soil.

(c) Alcohol is produced with the help of yeast.

(d) Cholera is caused by bacteria.

Q2. Tick the correct answer:

(a) Yeast is used in the production of 

(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen

Ans: (ii) alcohol

(b) The following is an antibiotic

(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast

Ans: (ii) Streptomycin

(c) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly

Butterfly

Ans: (i) female Anopheles mosquito

(d) The most common carrier of communicable diseases is

(i) ant (ii) housefly (iii) dragonfly (iv) spider

Ans: (ii) housefly 

(e) The bread or idli dough rises because of

(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading

Ans: (iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called

(i) nitrogen fixation (ii) molding (iii) fermentation (iv) infection

Ans: (iii) fermentation 

Q3. Match the organisms in Column I with their action in Column II.

Ans: 

Q4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Ans: The microorganism can not be seen with naked eyes. Microorganisms are too small and are not visible to the unaided eye. Some of these, such as the fungus that grows on bread can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Q5. What are the major groups of microorganisms?
Ans: Microorganisms are classified into four major groups:

1. Bacteria
2. Fungi
3. Protozoa
4. Algae
   
   

Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Ans: Bacteria like Rhizobium and blue-green algae are microorganisms which can fix atmospheric nitrogen in the soil thus increase soil fertility. These microbes are commonly called biological nitrogen fixers.

Blue-green algae

Q7. Write 10 lines on the usefulness of microorganisms in our lives.
Ans: Microorganisms are quite useful in our lives in many ways :

1. Yeast - a microorganism is used for the large scale production of alcohol, wine and acetic acid (vinegar).
2. Lactobacillus- a bacterial microorganism helps us in turning milk into curd.
3. Yeast a microorganism is used in baking industry for making bread, pastries and cakes.
4. Bacteria are also used for commercial production of antibiotics medicines like Streptomycin, tetracycline and erythromycin.
5. They help in Increasing Soil Fertility. Microorganisms like Rhizobium and blue-green algae are of great importance in agriculture.
6. They increase soil fertility by fixing atmospheric nitrogen and converting it into nitrogenous compounds.
7. Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is released to the atmosphere.
8. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.
9. Some microorganisms inside our bodies help in food digestion.

Q8. Write a short paragraph on the harms caused by microorganisms.
Ans: Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Pathogens spread a number of Microbial diseases or communicable diseases like cholera, common cold, chickenpox and tuberculosis from an infected person to a healthy person through air, water, food or physical contact.

Some microorganisms spoil food, clothing and leather. Food poisoning is caused due to the consumption of food spoilt by some microorganisms.

Microorganisms
Q9. What are antibiotics? What precautions must be taken while taking antibiotics?
Ans: Antibiotic is a medicine that kills or stops the growth of disease-causing microorganisms in humans and animals. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics medicines like Streptomycin, tetracycline and erythromycin are commercially produced from bacteria and fungi.

Antibiotics

Precautions in taking Antibiotics:

(i) Antibiotics should be taken only on the advice of a qualified doctor. And one must finish the course prescribed by the doctor.
(ii) Antibiotics must be avoided when not needed or required.
(iii) Antibiotics taken unnecessarily may kill the beneficial bacteria in the body.