NCERT Class 8 Science Chapter 2 Solution
Brief Information: This post contains the solution for Chapter 2 Microorganisms: Friend and Foe of Class 8 of the CBSE and also Gujarat Board (GSEB) books by GCERT (based on new NCERT).
The solution for Chapter 2 Microorganisms: Friend and Foe is given below
Q1. 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
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 A with their action in Column B.
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?
Ans. The microorganism cannot be seen with the naked eye. Their size is very small to be seen by the naked eye. Microscope is the instrument used to see the microorganism. It magnifies the image of the microbes so that we can see it. Some microorganism like fungi can be seed with the help of magnifying glass.
Q.5. What are the major groups of microorganisms?
Ans. The microorganism can be divided into following four major groups:
1. Bacteria
2. Fungi
3. Algae
4. Protozoa
Q.6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Ans. Rhizobium, Clostridium and Azotobacter the microorganisms which can fix atmospheric nitrogen in the soil.
Q.7. Write 10 lines on the usefulness of microorganisms in our lives.
Ans. Microorganism are very small organisms which can not be seen with naked eye. But, microorganism are useful in our lives in –
1. Making curd – Bacteria Lactobacillus coverts milk into curd.
2. Baking – Yeasts are used in the baking industry for making breads, pastries and cakes.
3. Commercial use – Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast are also used for commercial production of alcohol and wine using fermentation method.
4. Production of antibiotics – Bacteria and fungi are used in production of antibiotics e.g. Streptomycin, tetracycline and erythromycin
5. Making Vaccine – Several diseases are prevented by the use of vaccine e.g. cholera, tuberculosis, smallpox and hepatitis
6. Increase soil fertility – Some bacteria are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase it fertility. e.g. Rhizobium, Clostridium and Azotobacter
7. Decomposing – microorganisms decompose dead organic waste of plants and animals converting them into simple substances.
8. Oil spills – Microorganisms are used to deal with the environmental problem such as oil spills.
9. Production of vitamins and other nutrients.
10. Yogurt – Many microorganisms are consumed as probiotic for healthy living.
Q.8. Write a short paragraph on the harmful effects of microorganisms.
Ans. The microorganism can harm to human beings, animals and plants. The disease causing microorganisms are called pathogens.
-In human beings many fatal disease such as cholera, common cold, chicken pox and tuberculosis. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.
-In animals disease such as anthrax are caused by bacteria and foot and mouth disease are caused virus.
-In plants, microorganism cause disease and reduce their yield. Bhendi yellow vein mosaic disease is caused by a virus and is spread by insects in lady fingers. Rust of wheat is a fungal disease spread through air.
-Food poisoning – The food is spoilt by microorganism. Some microorganism release toxins (toxic substance) which can cause serious illness and even death.
Q.9. What are antibiotics? What precautions must be taken while taking antibiotics?
Ans. The medicines that are used to kill or stop the growth of the disease causing microorganisms are called Antibiotics. They are mostly derived from bacteria and fungi. e.g. Streptomycin, tetracycline and
erythromycin.
Precaution – 1.) The antibiotics should be taken only on the advice of qualified doctors. Also one must complete the course of antibiotics prescribed by the doctor. It should be borne in mind that antibiotics also kills the beneficial bacterial living in our gut. 2.) Antibiotics should not be taken against cold and flu as they are caused by virus and antibiotics will not be effective.