NCERT TEXT BOOK EXERCISES
Q1. 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) magnifying glass or microscope
(b) Nitrogen
(c) yeast
(d) a bacteria.
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) house fly
(iv) butter fly
(d) The most common carrier of communicable diseases is
(i) ant
(ii) house fly
(iii) dragon fly
(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
Ans. (a) (ii) alcohol
(b) (ii) streptomycin
(c) (i) female Anopheles mosquito
(d) (ii) housefly
(f) (iii) fermentation
Q3. Match the organisms in Column A with their action in Column B.
| Column A | Column 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.
| Column A | Column 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 |
Q4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Ans. The microorganisms are so small in size that they cannot be seen with the naked
eye. Some of these, such as fungus that grows on bread, can be seen with a
magnifying glass. Others cannot be seen without the help of a microscope. That is
why these are called microorganisms or microbes.
Q5. What are the major groups of microorganisms?
Ans. Microorganisms are classified into four major groups based on their size. These are:
(i) Bacteria (ii) Fungi
(iii) Protozoa (iv) Some algae.
Micro-organism Example
Bacteria: Spiral bacteria, Rod shaped bacteria
Algae: Clamydomonas, Spirogyra
Protozoa: Amoeba, Paramoecium
Fungus: Pencillium, Aspergillus, Bread mould
Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Ans. Rhizobium, Clostridium and Azotobactor.
Q7. Write 10 lines on the usefulness of microorganisms in our lives.
Ans. Microorganisms are useful for us in many ways e.g.,
(i) bacterium, lactobacillus convert milk into curd.
(ii) bacteria are also involved in the making of cheese.
(iii) Acetobacter aceti is used for production of Acetic acid from alcohol.
(iv) Yeast is used for commercial production of alcohol and wine.
(v) Antibiotics are manufactured by growing specific microorganisms.
(vi) Some bacteria fix atmospheric nitrogen and increase the soil fertility.
(vii) Bacteria are used in the preparation of medicines.
(viii) Bacteria are used in the formation of pickles and many other food items.
(ix) Yeast is also used in baking industry for making breads, pastries and cakes
Q8. Write a short paragraph on the harms caused by microorganisms.
Ans. Some microorganisms harm us in various ways e.g.,
(i) Many organisms are disease causing e.g.,
Common ailments like cold, influenza (flu) and most coughs are caused b; viruses.
Serious diseases like, polio and chicken pox are also caused by viruse-
Deseases like dysentery and malaria are caused by protozoan.
Typhoid and tuberculosis (TB) are caused due to bacteria.
Ring worm is caused due to fungi.
Foot and mouth disease of cattle is caused due to virus.
Anthrax a dangerous human and cattle disease is caused by a bacteria.
(ii) Some microorganisms release toxic substances when grow on food items.
(iii) Some microorganisms spoil leather items, wooden-work and lenses.
Q9. What are antibiotics? What precautions must be taken while taking antibiotics?
Ans. Antibiotics are the medicines which kill or stop the growth of the disease causing microorganisms. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases.
It is important to remember that antibiotics should be taken only on the advice of a qualified doctor. Also you must finish the course prescribed by the doctor. If you take antibiotics when not needed, you help bacteria in your body to develop resistance to them. Next time when you fall ill and need these antibiotics, they would be less effective. Antibiotics, however, are not effective against cold and flu as they are caused by viruses.