NCERT Textbook Questions on Microorganisms PDF

2.Microorganisms: Friend and Foe NCERT Textbook Questions Q 1. Fill in the blanks. (a) Microorganisms can be seen with the help of a microscope. (b) Blue-green algae fix nitrogen directly from the air to enhance the fertility of soil. (c) Alcohol is produced with the help...

2.Microorganisms: Friend and Foe NCERT Textbook Questions Q 1. Fill in the blanks. (a) Microorganisms can be seen with the help of a microscope. (b) Blue-green algae fix nitrogen directly from the air to enhance the 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 Answer: (ii) alcohol (b) The following is an antibiotic: (i) sodium bicarbonate (ii) streptomycin (iii) alcohol (iv) yeast Answer: (ii) streptomycin (c) Carrier of malaria-causing protozoan is: (i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly Answer: (i) female Anopheles mosquito (d) The most common carrier of communicable diseases is (i) ant (ii) housefly (iii) dragonfly (iv) spider Answer: (ii) housefly Page 1 of 6 (e) The bread or idli dough rises because of: (i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading Answer:(iii) growth of yeast cells (f) The process of conversion of sugar into alcohol is called (i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infectio n Answer: (iii) fermentation Q 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 Answer: (i) (e) (ii) (a) (iii) (b) iv (c) (v)(d) (vi)(f) Q 4. Can microorganisms be seen with the naked eye? If not, how can they be seen? Ans: Micro-organisms are too small to be seen through naked eyes. They can be seen with the help of a magnifying glass or microscope. For example, fungus that grows on bread is so small that it can be seen only with the help of a magnifying glass or microscope.. Q 5. What are the major groups of microorganisms? Ans: There are four major groups of micro-organisms: (i) Bacteria − They are single celled disease-causing micro-organisms. They can be spiral or rod- shaped. (ii) Fungi − They are mostly multicellular disease-causing microbes. Bread moulds are common examples of fungi. (iii) Protozoa − They are unicellular. They mainly include Page 2 of 6 organisms such as Amoeba, Plasmodium (iv) Algae − They include multicellular, photosynthetic organisms such as Spirogyra, Chlamydomonas, etc. Some microbiologists also classify viruses as microorganisms, but other consider these as non – living. They are those microbes which reproduce only inside the cells of host organisms. They cause diseases like cold, polio, AIDS etc. Q 6. Name the microorganisms which can fix atmospheric nitrogen in the soil. Ans: Rhizobium, Clostridium and Azotobacter. Q7. Write 10 lines on the usefulness of microorganisms in our lives. Ans: Microorganisms are useful to us in many ways. For example, Bacteria like Lactobacillus convert milk into curd. Bacteria are also involved in the making of cheese. Acetobacter aceti is used for producing acetic acid from alcohol. Yeast is used in the commercial production of alcohol, wine and bakery products. Some specific microorganisms are helpful in manufacturing of antibiotics. Microorganisms act as cleansing agents and decompose the waste products into manure. Dead or weakened microbes are used in the preparation of vaccines. Some bacteria fix atmospheric nitrogen and increase soil fertility. Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption. Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed. Q 8. Write a short paragraph on the harms caused by microorganisms. Ans: Harmful effects of micro-organisms: Micro-organisms cause diseases in animals. For example, in humans, bacteria cause diseases such as tuberculosis, cholera, typhoid, etc. In cattle, the foot and mouth disease are caused by a virus. Also, several microbes cause diseases in plants. For example, the productivity of wheat, orange, apple, etc. is reduced due to microbial diseases in plants. Certain microbes, on entering into our body, produce toxic substances. This leads to food poisoning. Some micro-organisms such as fungus spoil our food. For example, bread when left unused under moist conditions gets spoilt by fungus, producing a white cotton-like growth on the bread. Page 3 of 6  Q 9. What are antibiotics? What precautions must be taken while taking antibiotics? Ans: Antibiotics are medicines produced by certain micro-organisms to kill other disease-causing micro-organisms. These medicines are commonly obtained from bacteria and fungi. Streptomycin, tetracycline, penicillin, etc. are common antibiotics. Precautions to be taken while using antibiotics: (i) Antibiotics should be taken under the supervision of a well-qualified doctor. (ii) Course (intake) of antibiotics should be completed as per the prescription given by the doctor. (iii) Antibiotics should be taken in the right amount and at the right time. A wrong dose of antibiotics makes the drug ineffective. Also, excessive consumption of drugs may kill the useful bacteria present in our body. Q.10 Assertion and Reasoning questions: - In the following questions, two statements are given- one labelled Assertion(A) and the other labelled Reason (R). Read the statements carefully and choose the correct alternative as given below: - 1. Assertion(A): Microorganisms are also called microbes. Reason(R): As microorganisms are so small in size that they cannot be seen with naked eyes. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is not the correct explanation of A c) A is true but R is false d) A is false but R is true Answer: a) Both A and R are true and R is the correct explanation of A 2. Assertion(A): Hepatitis A is a disease transmitted in human beings by water. Reason (R): It is a disease caused by a microorganism called bacteria. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is not the correct explanation of A c) A is true but R is false d) A is false but R is true Answer: c) A is true but R is false ****************** Page 4 of 6