Ncert solutions science class 8 Solutions for Chapter 2 microorganisms friend and foe

Yeast is used in the production of

Fill in the blank:

Blue green algae fix __________ directly from air and enhance fertility of soil.

Fill in the blank:

Alcohol is produced with the help of _________.

Fill in the blank:

Cholera is caused by _________.

Fill in the blank:

Microorganisms can be seen with the help of a ___________.

The process of conversion of sugar into alcohol is called

The bread or idli dough rises because of

The most common carrier of communicable diseases is

Carrier of malaria causing protozoan is

The following is an antibiotic

Fill in the blanks.

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

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

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

(d) Cholera is caused by __________.

Q1) Fill in the blanks.

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

b)Blue green algae fix __________ directly from air and enhance fertility

of soil.

c) Alcohol is produced with the help of __________.

d) Cholera is caused by __________.

Which of the following reproduces only inside a host cell?

(a) Bacteria

(b) Virus

(c) Amoeba

(d) Fungus.

Tick the correct answer.

(a) Yeast is used in the production of

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

(b) The following is an antibiotic

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

(c) Carrier of malaria-causing protozoan is

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

(d) The most common carrier of communicable diseases is

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

(e) The bread or idli dough rises because of

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

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

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

Q2) Tick the correct answer.

a) Yeast is used in the production of

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

b) The following is an antibiotic

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

c) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito (ii) cockroach

(iii) housefly (iv) butterfly

d) The most common carrier of communicable diseases is

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

e) The bread or idli dough rises because of

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

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

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

A disease in human beings caused by virus is _______.

(a) typhoid

(b) influenza

(c) dysentry

(d) cholera

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

(a) pain killer

(b) antibodies

(c) antibiotics

(d) vaccines

Q3) Match the organisms in Column A with their action in Column B.

Match the organisms in Column A with their action in Column B.

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

(a) fungus and protozoa

(b) alga and bacteria

(c) bacteria and protozoa

(d) alga and fungus

Q4) Can microorganisms be seen with the naked eye? If not, how can they be seen?

Can microorganisms be seen with the naked eye? If not, how can they be seen?

The gas released during the preparation of bread is

(a) oxygen

(b) carbon dioxide

(c) nitrogen

(d) sulphur dioxide

Q5) What are the major groups of microorganisms?

Q6) Name the microorganisms which can fix atmospheric nitrogen in the soil.

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

(a) dengue

(b) malaria

(c) polio

(d) measles

Name the microorganisms which can fix atmospheric nitrogen in the soil.

What are the major groups of microorganisms?

Q7) Write 10 lines on the usefulness of microorganisms in our lives.

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

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?

(a) Waste in pit A degraded faster than that in pit B.

(b) Waste in pit B degraded faster than that in pit A.

c) Waste in both pits degraded almost equally.

(d) Waste in both pits did not degrade at all.

Write a short paragraph on the harmful effects of microorganisms.

Unscramble the jumbled words underlined in the following statements.

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

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

(c) Xanrhat is a dangerous bacterial disease.

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

Q8) Write a short paragraph on the harmful effects of microorganisms.

Q9) What are antibiotics? What precautions must be taken while taking antibiotics?

Suggest a suitable word for each of the following statements.

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

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

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

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

What are antibiotics? What precautions must be taken while taking antibiotics?

Match the names of scientists given in Column A with the discovery made by them given in Column B.

Column A Column B

(a) Louis Pasteur (i) Penicillin

(b) Robert Koch (ii) anthrax bacterium

(c) Edward Jenner (iii) Fermentation

(d) Alexander Fleming (iv) small pox

Name one commercial use of yeast

Name the process in yeast that converts sugars into alcohol.

In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?

Why should we avoid standing close to a tuberculosis patient while he/she is coughing?

Polio drops are not given to children suffering from diarrhoea. Why?

Paheli watched her grandmother making mango pickle. After she bottled the pickle, her grand mother poured oil on top of the pickle before closing the lid. Paheli wanted to know why oil was poured? Can you help her understand why?

Match the microorganisms given in the Column A to the group to which they belong in Column B.

Column A Column B

(a) Lactobacillus (i) Algae

(b) Aspergillus (ii) Protozoa

(c) Spirogyra (iii) Fungi

(d) Paramecium (iv) Bacteria

Classify the following into friendly and harmful microorganisms.

Yeast, malarial parasite, Lactobacillus, bread mould, Rhizobium, Bacillus anthracis

What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left in the open for a day or two?

(a) Name two diseases that are caused by virus.

(b) Write one important characteristic of virus.

Observe the Fig. and answer the questions that follows.

(a) Write the name of the disease.

(b) Name the causative agent of this disease?

(c) How does the disease spread from one plant to another?

(d) Name any two plant diseases and the microbes that cause them.

How do vaccines work?

Observe the set up given in Fig. and answer the following questions.

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

(b) Which gas is released in A?

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

Observe the Fig and answer the following questions.

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

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

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

(d) Is it safe to eat infected bread?

Give reasons for the following.

(a) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed without boiling.

(b) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside.

(c) Farmers prefer to grow beans and peas in nitrogen deficient soils.

(d) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?

How can we prevent the following diseases?

(a) Cholera

(b) Typhoid

(c) Hepatitis A

Complete the following cycle given as Fig. 2.4 by filling the blanks (a), (b), (c) (d)