NCERT Solutions for Class 8th Science
Chapter 2 – MICROORGANISMS : FRIEND AND FOE
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.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_.
(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_.
Q.2 Tick the correct answer:
(a) Yeast is used in the production of
(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen
Ans (ii) alcohol
(b) The following is an antibiotic
(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
Ans (ii) Streptomycin
(c) Carrier of malaria-causing protozoan is
(i) Female Anopheles mosquito (ii) cockroach
(iii) housefly (iv) butterfly
Ans (i) Female Anopheles mosquito
(d) The most common carrier of communicable diseases is
(i) ant (ii) housefly (iii) dragonfly (iv) spider
Ans (ii) Housefly
(e) The bread or idli dough rises because of
(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
Ans (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
Ans (iii) Fermentation
Q.3 Match the organisms in Column I with their action in Column II.
Column I Column II
(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 (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
Q.4 Can microorganisms be seen with the naked eye? If not, how can they be seen?
Q.5 What are the major groups of microorganisms?
Q.6 Name the microorganisms which can fix atmospheric nitrogen in the soil.
Q.7 Write 10 lines on the usefulness of microorganisms in our lives.
Q.8 Write a short paragraph on the harms caused by microorganisms.
Ans Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some............
Q.9 What are antibiotics? What precautions must be taken while taking antibiotics?
Ans The medicines produced by microorganisms that kill or stop the growth of disease-causing microorganisms are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Some of the common examples are Streptomycin, tetracycline and erythromycin. Precautions to be taken while using antibiotics are:
1) Antibiotics should be taken only on the advice of a qualified doctor.
2) The course of taking antibiotics must be completed as prescribed by the doctor.
3) Antibiotics must be taken only when they are needed and in adequate amount.