Ncert Exemplar Solutions Class 8 Science Microorganisms Friend and Foe

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Ncert Exemplar Solutions Class 8 Science Microorganisms Friend and Foe

Welcome to NCTB Solutions. Here with this post we are going to help 8th class students for the Solutions of NCERT Exemplar Class 8 Science Book, Unit 2, Microorganisms Friend and Foe. Here students can easily find step by step solutions of all the problems for Microorganisms Friend and Foe, Also here our Science teacher’s are solved all the questions with easily understandable language with proper guidance so that all the students can understand easily.

Microorganisms Friend and Foe Solution :

Multiple Choice Questions :

Question no – (1)

Which of the following reproduces only inside a host cell?

Answer : 

The correct answer is option – (b)

Virus reproduces only inside a host cell.

Question no – (2)

A disease in human beings caused by virus is ___

Answer : 

The appropriate answer is option – (b)

A disease in human beings caused by virus is Influenza.

Question no – (3)

Pathogenic micro-organisms present in host cells are killed by medicines called

Answer : 

The correct answer is alternative – (c)

Antibiotics medicines kill’s the pathogenic micro-organisms present in host cells.

Question no – (4)

The two micro-organisms which live in symbiotic association in lichens are

Answer : 

The correct option is – (d)

The two micro-organisms which live in symbiotic association in lichens are alga and fungus.

Question no – (5)

The gas released during the preparation of bread is

Answer : 

The correct answer is option – (b)

The gas released during the preparation of bread is Carbon Dioxide.

Question no – (6)

The disease caused by a protozoan and spread by an insect is

Answer : 

The appropriate option is (b)

The disease caused by a protozoan and spread by an insect is Malaria.

Question no – (7)

Paheli dug two pits, A and B, in her garden. In pit A, she put a polyhtene bag packed with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month?

Answer : 

The correct answer is alternative – (b)

She will observe that,

Waste in pit B degraded faster than that in pit A.

Very Short Answer Questions :

Question no – (8) 

Answer :

(a) Cells of our body produce antibodies to fight pathogens.

(b)Tuberculosis is an air-borne disease caused by a bacterium.

(c) Anthrax is a dangerous bacterial disease.

(d) Yeasts are used in the wine industry because of their property of fermentation.

Question no – (9) 

Answer :

(a) Chemicals added to food to prevent growth of microorganisms

= Preservatives

(b) Nitrogen-fixing microorganism present in the root nodules of legumes

= Rhizobium

(c) Agent which spreads pathogens from one place to another

= Carrier

(d) Chemicals which kill or stop the growth of pathogens

= Antibiotics

Question no – (10) 

Answer :

(a) Louis Pasteur → (iii) Fermentation.

(b) Robert Koch → (ii) anthrax bacterium.

(c) Edward Jenner → (iv) small pox vaccine.

(d) Alexander Fleming → (i) Penicillin.

Question no – (11) 

Answer :

Yeasts are commercially used in the production of alcohol and wine.

Question no – (12) 

Answer :

Fermentation is the process that converts sugar into alcohol.

Question no – (13) 

Answer :

Nitrogen is enriched by the blue green algae or cyanobacteria.

Question no – (14) 

Answer :

We should avoid standing close to a tuberculosis patient because tuberculosis is a communicable disease and it can easily spread from one person to another by means of air transmission.

Question no – (15) 

Answer :

Polio drops are usually not given to children suffering from diarrhoea because as he is suffering from diarrhoea the polio drops may be removed from the body due to repetitive excretions.

Question no – (16) 

Answer :

Grandmother poured some oil while bottling the pickle because oil prevents the growth of bacteria, fungus and viruses on the pickle thus making it last for a long time.

Short Answer Questions : 

Question no – (17) 

Answer :

(a) Lactobacillus → (iv) Bacteria

(b) Aspergillus → (iii) Fungi

(c) Spirogyra → (i) Algae

(d) Paramecium → (ii) Protozoa

Question no – (18) 

Answer :

Friendly : Yeast, Lactobacillus, Rhizobium.

Harmful : Malarial Parasite, Bread mould, Bacillus Anthracis.

Question no – (19) 

Answer :

He must have fell ill because the chat that he ate before must have been contaminated by harmful microorganisms.

Question no – (20) 

Answer : 

If the poris and unused kneaded flour is left in the open for one two days then the unused kneaded flour will probably get contaminated by microbes that causes fermentation in the flour and makes it unedible while the poris on the other hand will stay fir to eat for a long time as it was cooked in boiling oil.

Question no – (21) 

Answer : 

(a) The two diseases that are caused by virus are Chicken pox and Polio.

(b) One important characteristics of virus is –

• Virus reproduce only in the cells of host organisms.

Question no – (23) 

Answer : 

Vaccines are nothing but the weakened viruses of the diseases for which we are trying to get immunity of. When the vaccine is injected into a person the person’s immunity starts to fight the disease and produce antibodies which will later protect the person during later invasion of that virus.

Question no – (24) 

Answer : 

(a) What happens to the sugar solution in A?

The sugar water solution in beaker A will change to alcohol as the yeast in it changes sugar to alcohol by the process of fermentation.

(b) Which gas is released in A?

= Carbon dioxide gas is released in A as it is the by product of fermentation.

(c) What changes will you observe in B when the released gas passes through it

= The lime water in beaker B will change into milky colour.

Question no – (25) 

Answer : 

(a) Name the microorganism and the group to which it belongs.

= It is a bread mould and it belongs to fungi group.

(b) Name the food item on which the organism grows.

= It grows on the surfaces of moist breads

(c) Does it grow well in dry or in moist conditions?

= It grows very well in moist conditions.

(d) Is it safe to eat infected bread?

= No it is not at all safe to eat infected bread because the breads are spoiled and it emits foul smell that is not good for us.

Question no – (26) 

Answer : 

(a) Fresh milk is usually boiled before eating because it has a lot of microorganisms present on it which will die if we boil it. On the other hand processed milk need not to be boiled because the milk is already pasterurised that is it is already boiled to kill the microbes in it.

(b) Raw vegetables and fruits are usually kept in refrigerators because microbes don’t grow in cold temperatures so they can’t infect them if they are kept in refrigerators. Whereas pickles and jams can be kept in open because they are protected from the microbes as they can’t grow in salt or sugar.

(c) Farmer’s prefer to grow beans and peas in nitrogen deficient soils as beans and peas both are legumes, the roots of both these plants have Nitrogen fixing bacteria that fixes the atmospheric nitrogen into the soil to enrich the soil and improve its fertility.

(d) Mosquitoes can be controlled by preventing the stagnation of water because even though they don’t live on it they grow on it. The mosquitoes lays eggs on stagnant water where they grow to become adult mosquitoes. So if we prevent the stagnation of water we could control the population of mosquitoes.

Question no – (28) 

Answer : 

(a) Lighting.

(b) Nitrogen fixing bacteria fixes atmospheric nitrogen.

(c) Nitrogenous waste from excretion or death.

(d) Bacteria turns compounds of nitrogen into gaseous nitrogen.


Other Chapter Solutions : 

👉 Crop Production and Management

👉 Synthetic Fibres and Plastics

👉 Materials : Metals and Non-Metals

👉 Coal and Petroleum

👉 Combustion and Flame

👉 Conservation of Plants and Animals

👉 Cell-Structure and Functions

👉 Reproduction in Animals

👉 Reaching the Age of Adolescence

👉 Force

👉 Friction

👉 Sound

👉 Chemical Effects of Electric Current

👉 Some Natural Phenomena

👉 Light

👉 Stars and Solar System

👉 Pollution of Air and Water

Updated: June 28, 2023 — 3:42 pm

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