Microorganisms : Friend and Foe, NCERT Solutions, Class 8, Science Class 8 Notes | EduRev

Class 8 : Microorganisms : Friend and Foe, NCERT Solutions, Class 8, Science Class 8 Notes | EduRev

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Microorganism: Friend and Foe

Solution: NCERT Exercise

Question: 1. Fill in the blanks:

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

Answer: Microscope

(b) Blue green algae fix __________ directly from air to enhance fertility of soil.

Answer:- Nitrogen

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

Answer:- Yeast

(d) Cholera is caused by __________.

Answer: Bacteria

Question: 2. Tick the correct answer:

(a) Yeast is used in the production of

(1) Sugar

(2) Alcohol

(3) Hydrochloric acid

(4) Oxygen

Answer: (2) Alcohol

(b) The following is an antibiotic

(1) Sodium bicarbonate

(2) Streptomycin

(3) Alcohol

(4) Yeast

Answer: (2) Streptomycin

(c) Carrier of malaria-causing protozoan is

(1) Female Anopheles mosquito

(2) Cockroach

(3) Housefly

(4) Butterfly

Answer: (1) Female Anopheles mosquito

(d) The most common carrier of communicable diseases is

(1) Ant

(2) Housefly

(3) Dragonfly

(4) Spider

Answer: (2) Housefly

(e) The bread or idli dough rises because of

(1) Heat

(2) Grinding

(3) Growth of yeast cells

(4) Kneading

Answer: (3) Growth of yeast cells

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

(1) Nitrogen fixation

(2) Moulding

(3) Fermentation

(4) Infection

Answer: (3) Fermentation

Question: 3. Match the organisms in Column I with their action in

Column AColumn B
BacteriaFixing nitrogen
RhizobiumSetting of curd
LactobacillusBaking of bread
YeastCausing malaria
A protozoanCausing cholera
A virusCausing AIDS
 Producing antibodies


Column AColumn B
BacteriaCausing cholera
RhizobiumFixing nitrogen
LactobacillusSetting of curd
YeastBaking of bread
A protozoanCausing malaria
A virusCausing AIDS

Question: 4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: Microorganisms cannot be seen with naked eye. They can be seen through a microscope.

Question: 5. What are the major groups of microorganisms?

Answer: The major groups of microorganisms are: Bacteria, Virus, Fungi and Protozoa.

Question: 6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: Rhizobium bacteria carry out nitrogen fixation in soil.

Question: 7. Write 10 lines on the usefulness of microorganisms in our lives.

Answer: Following are the benefits of microorganisms in our lives:

(a) Lactobacillus causes setting of curd.

(b) Rhizobium helps in nitrogen fixation in soil.

(c) Yeast helps in making fluffy bread and cake.

(d) Some bacteria facilitate retting of jute.

(e) Some bacteria facilitate tanning of leather.

(f) Blue green algae carry out nitrogen fixation.

(g) Penicillium; a fungi; is used to produce antibiotics.

(h) Many microbes carry out decomposition of dead remains of plants and animals.

(i) Yeast causes fermentation which is utilised to produce alcohol.

(j) Processing and ageing of cheese is carried out by microorganisms.

Question: 8. Write a short paragraph on the harms caused by microorganisms.

Answer: Microorganisms can also be harmful to us. Many microbes which reside in our body may turn pathogenic and can cause serious diseases. Many microbes from outside can enter our body and cause diseases. Some microbes lead to rotten food which leads to large scale damage. Sometimes, eating contaminated food may lead to food poisoning which can also prove lethal.

Question: 9. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: Medicines which are given to kill bacteria are called antibiotics. Antibiotics are helpful tools to fight most of the diseases. But use of antibiotics should be done with certain cautions in mind. Never take an antibiotic without advice from a doctor. Before taking an antibiotic, check for date of expiry on the packet. Take the dose as advised by the doctor. Keep the antibiotic away from the reach of children.

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