NCERT Solutions Class 8 Science
The NCERT Solutions in English Language for Class 8 Science Chapter – 2 (Microorganisms: Friend and Foe) has been provided here to help the students in solving the questions from this exercise.
Chapter – 2 (Microorganisms : Friend and Foe)
1. Fill in the blanks.
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue-green algae fix __________ directly from the air and enhance the fertility of the soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.
Answer –
(a) Microorganisms can be seen with the help of a Microscope.
(b) Blue-green algae fix Nitrogen directly from the air and enhance the fertility of the soil.
(c) Alcohol is produced with the help of Yeast.
(d) Cholera is caused by Bacteria- Vibrio cholera.
2. Tick the correct answer.
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer – (ii) alcohol
(b) The following is an antibiotic
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
Answer – (ii) Streptomycin
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer – (i) female Anopheles mosquito
(d) The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
Answer – (ii) housefly
(e) The bread or idli dough rises because of
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading
Answer – (iii) growth of yeast cells
(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation
(ii) moulding
(iii) fermentation
(iv) infection
Answer – (iii) fermentation
3. Match the organisms in Column A with their action in Column B.
| A | B |
| (i) Bacteria | (a) Fixing nitrogen |
| (ii) Rhizobium | (b) Setting of curd |
| (iii) Lactobacillus | (c) Baking of bread |
| (iv) Yeast | (d) Causing malaria |
| (v) A protozoan | (e) Causing cholera |
| (vi) A virus | (f) Causing AIDS |
| (g) Producing antibodies |
Answer –
| A | B |
| (i) Bacteria | (e) Causing cholera |
| (ii) Rhizobium | (a) Fixing nitrogen |
| (iii) Lactobacillus | (b) Setting of curd |
| (iv) Yeast | (c) Baking of bread |
| (v) A protozoan | (d) Causing malaria |
| (vi) A virus | (f) Causing AIDS |
4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer – Microorganisms cannot be seen by the naked eye because they are very small. They can be seen by using a microscope.
5. What are the major groups of microorganisms?
Answer – The major groups of microorganisms are as follows:
- Bacteria
- Fungi
- Protozoans
- Algae
- Viruses
6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer – Bacteria like Rhizobium, Azotobacter and blue green algae like Anabaena and Nostoc can fix atmospheric nitrogen in the soil in form of nitrogenous compounds.
7. Write 10 lines on the usefulness of microorganisms in our lives.
Answer – Microorganisms are very useful to us. They help us in following ways:
- Microorganisms help us in food sector. They are used for curdling of milk, preparation of bread, cake, etc.
- Microorganisms are used to produce alcohol at large scale.
- They are also used to produce wine.
- Yeast is used in bakeries.
- They are also used as preservatives for food items.
- They are used to make different medicines, especially the antibiotics.
- Microorganisms are used to prepare vaccines for various diseases.
- They are useful for agriculture sector, as they enhance the fertility of soil by fixing nitrogen.
- They work as natural cleaners, as they decompose the dead bodies of plants and animals.
- Microorganisms prepare manures by decomposing dead bodies of plants and animals.
8. Write a short paragraph on the harmful effects of microorganisms.
Answer – Microorganisms are useful as well as harmful also, in fact, some microbes are very helpful but most of them are harmful to living beings.
- Some microorganisms are pathogens which cause diseases to human animals and plants.
- Bacteria and fungi are well known to cause food spoilage and make them unfit for eating.
- Bacteria cause some diseases like cholera, typhoid, and diarrhea through water and food.
- Virus scan causes smallpox, cold, hepatitis polio and soon.
- Some microorganisms show antibiotic resistance to certain diseases.
9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer – Antibiotics are antimicrobial drugs obtained from other organisms to combat harmful microorganisms. Precautions to be taken while using antibiotics:
- Antibiotics should be taken under the supervision of a well qualified doctor.
- Course (intake) of antibiotics should be completed as per the prescription given by the doctor.
- Antibiotics should be taken in the right amount and at the right time. A wrong dose of antibiotics makes the drug ineffective. Also, excessive consumption of drugs may kill the useful bacteria present in our body.
