Microorganisms: Friend and Foe (NCERT solution, Class 8)

(1)Fill in the blanks-

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

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

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

(d) Cholera is caused by ______.

Ans-

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

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

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

(d) Cholera is caused by bacteria.

(2) Tick the correct answer.

(a) Yeast is used in the production of

(i) sugar

(ii) alcohol

(iii) hydrochloric acid

(iv) oxygen

Ans-

(ii)Yeast is used in the production of alcohol.

(b) The following is an antibiotic

(i) Sodium bi carbonate

(ii) Streptomycin

(iii) Alcohol

(iv) Yeast

Ans-

(ii) Streptomycin is an antibiotic.

(c) Carrier of malaria – causing protozoan is

(i) female Anopheles mosquito

(ii) cockroach

(iii) housefly

(iv) butterfly

Ans-

(i) Carrier of malaria – causing protozoan is female Anopheles mosquito.

(d) The most common carrier of communicable disease is

(i) ant

(ii) housefly

(iii) dragonfly

(iv) spider

Ans-

(ii)The most common carrier of communicable disease is housefly.

(e)The bread or idli dough rises because of

(i)Heat

(ii) grinding

(iii) growth of yeast cells

(iv) kneading

Ans-

(iii) The bread or idli dough rises because of growth of yeast cells.

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

(i) nitrogen fixation

(ii) moulding

(iii) fermentation

(iv) infection

Ans-

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

Ans-

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?

Ans- Microorganisms can not be seen with the naked eye because they are very small organisms. They can be seen by microscope.

(5) What are the major groups of microorganisms?

Ans- The major groups of microorganisms are discussed below:-

(i)Bacteria are single-celled tiny living organisms which cannot be seen by naked eyes. They are responsible for diseases like typhoid and tuberculosis (TB) and fermentation of wine.

(ii)Fungi are single-celled tiny living organisms which cannot be seen by naked eyes. Fungi take their food from decay materials. Mushroom, yeast, rust are some example of it. Fungi are responsible for the infection in mouth and throat, skin itching, ring warm and many other infections.

(iii)Protozoa are single-celled tiny living organisms which cannot be seen by naked eyes. Protozoa (Amoeba) live alone. They are responsible for the diseases like malaria, dysentery.

(iv) Algae are single-celled tiny living organisms. They grow in water or on damp surface. They can perform photosynthesis because of chlorophyll presents in them.

(v) Viruses are single-celled tiny living organisms.They reproduce only inside the cells of the host organism which may be a bacterium, plant or animal. They are responsible for the diseases like cold, influenza, polio, chicken pox and most cough.

(6) Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans- Rhizobium is the microorganisms which can fix atmospheric nitrogen in the soil.

(7) Write 10 lines on the usefulness of microorganisms in our lives.

Ans-

(i) Microorganism Lactobacillus, the bacterium is responsible for the formation of curd.

(ii) Bacteria are also helpful in making cheese.

(iii) Yeast multiply very fast and increase the volume of dough which is used in baking food items as bread, cake, pastries etc.

(iv)Microorganism breaks the organic waste into harmless and usable humus which is used in fields and clean the environment.

(v) Animal waste which is fermented by microorganisms is used as manure for the plants which increase fertility of soil. Some bacteria and blue green algae are able to fix atmospheric nitrogen and increase the fertility of soil.

(vi) Microorganisms are used for the production of alcohol and vinegar by fermentation of barley, fruit juice, wheat, rice, etc.

(vii) Microorganisms are used for the production of pickles.

(viii) Microorganisms are used in making bhtura and idli.

 (ix) We take antibiotics when fall ill. Bacteria and fungi are the microorganisms which are used in the production of these antibiotics. Sterptomycin, tetracycline and penicillin are some examples of antibiotics.

(x) Vaccine is a substance which produced antigens (antibiotics) when microbes enter in to our body to save our body. Several diseases like cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

(8) Write a short paragraph on the harms caused by microorganisms.

Ans-

Microorganisms are responsible for many diseases in humans, plants and animals. Pathogens microorganisms are responsible for the diseases caused by the microorganisms. Those diseases which can be transferred or communicate by an infected person to a healthy person via air, water, food or with contact are known as communicable diseases.

Eg:- Cold spreads when tiny droplets of infected persons travel at the time of sneezing to healthy person via air.

Carriers are those insects and animals which carry microbes to the healthy persons.

Eg:- Housefly and mosquitoes.

When these carriers sits on garbage or animal excreta pathogens stick to them. When these flies sit on the uncovered food they leave pathogens on food which makes healthy people sick when they eat it.

Malaria, cholera, typhoid, tuberculosis are some major diseases which is caused by microorganisms in human.

(9) What are antibiotics? What precautions must be taken while taking antibiotics?

Ans- Antibiotics are the medicines which are helpful in fighting against diseases. Bacteria and fungi are the microorganisms which are used in the production of these antibiotics. Streptomycin, tetracycline and penicillin are some examples of antibiotics.

Precautions must be taken while taking antibiotics

(i)Antibiotics should be taken with the consultation of doctors.

(ii) Antibiotics should be taken at suggested time by doctors.

(iii)The course of antibiotics should be completed.

Helping Topics

Microorganisms: friend and foe

Practice sheet,class 8

Vaccination

Fermentation

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