NCERT Solutions for Class 8 Science Chapter 2 Microorganisms : Friend and Foe is provided here to help students in solving exercise questions provided in NCERT Class 8 Textbook. This Solution provides you with detailed answers to all the exercise questions.
This solution comprises various types of questions such as fill in the blanks, match the following, true or false, descriptive type questions from chapter 2 of the NCERT Class 8 Textbook. These answers will help you to attain perfection on the concepts involved in chapter Microorganisms : Friend and Foe
After studying this solution students will be able to gather knowledge on microorganisms, their habitats, classes of microorganisms like bacteria, fungi, protozoans and viruses, mode of their reproduction, use of microorganisms, harmful microorganisms, pathogens, soil microorganisms, nitrogen fixation by bacteria.
The NCERT Solution for Science Class 8 Chapter 2 Microorganisms : Friend and Foe is an important study material for the students of 8th standard. The NCERT Solutions for Class 8 Science provided here are helpful for the students to clear all their doubts in the chapter in an easy and interesting way.
1. 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 ___________.
Answer:
(a) Microscope
(b) Nitrogen
(c) Yeast
(d) Bacteria - Vibrio cholera
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
(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) infection
Answer:
(iii) fermentation
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 of malaria
(v) A Protozoans (e) Causing cholera
(vi) A Virus (f) Causing AIDS
(g) Producing antibodies
Answer:
(i) Bacteria - (e) Causing Cholera
(ii) Rhizobium - (a) Fixing nitrogen
(iii) Lactobacillus - (b) Setting of curd
(iv) Yeast - (c) Baking of bread
(v) A Protozoans - (d) Causing of malaria
(vi) A virus - (f) Causing AIDS
4. Can microorganisms be seen with the nake eye ? If not, how can they be seen ?
Answer:
Microorganisms cannot be seen by the naked eye because they are very small. They can be seen by using a microscope.
5. What are the major groups of microorganisms ?
Answer:
Major group of microorganisms are as follows :
- Bacteria
- Fungi
- Protozoans
- Algae
- Viruses
6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Rhizobum
7. Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Uses of microorganisms are listed below :
- They are helpful in cleaning up for the environment. For example, the organic wastes (vegetables peels, remains of animals, faeces etc.) are broken down into harmless and usable substance by bacteria.
- Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
- Bacteria are also involved in the making of cheese, pickles and many other food items.
- Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
- Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
- Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).
- Antibiotics are being produced from bacteria and fungi.
- Microorganisms are helpful in producing vaccines against disease-causing agents.
- Some bacteria are able to fix nitrogen from the atmosphere to enrich the soil with nitrogen and increase its fertility.
- Microorganisms decompose dead organic waste of plants and animals to convert them into simple substances. These substances are again used by the other plants and animals. Thus, microoraganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.
8. Write a short paragraph on the harmful effects of microorganisms.
Answer:
Microorganisms cause disease in plants and animals. For ex :- Cholera in humans is caused by bacteria called Vibrio cholera. In animals, the virus causes foot and mouth disease. Microorganisms spoil the food by decomposing the food material. Some microoraganisms spoil leather and clothes. Microoragnisms are responsible for food poisioning.
9. What are antibiotics ? What precautions must be taken while taking antibiotics ?
Answer:
Chemicals agents that kill or stop the growth of disease-causing microorganisms are called antibiotics. Antibiotics should be taken only on the advice of a qualified doctor. Also, one must complete the course prescribed by the doctor.
