Microorganisms: friend and foe class 8 Science NCERT Solutions

Microorganisms: friend and foe class 8 Science NCERT Solutions: Microorganisms: friend and foe is the chapter 2 from class 8 Science NCERT. Here you'll get Microorganisms: friend and foe class 8 Science/Microorganisms: friend and foe class 8 Science NCERT Solutions.

Microorganisms: friend and foe class 8 Science Main Points

Microorganisms are too small and are not visible to the unaided eye. They can live in all kinds of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.

Microorganisms are found in air, water and in the bodies of plants and animals. They may be unicellular or multicellular. Microorganisms include bacteria, fungi, protozoa and some algae. Viruses, though different from the above mentioned living organisms, are considered microbes.

Viruses are quite different from other microorganisms. They reproduce only inside the host organism: bacterium, plant or animal cell.

Some microorganisms are useful for commercial production of medicines and alcohol. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.

Protozoans cause serious diseases like dysentery and malaria. Some of the microorganisms grow on our food and cause food poisoning. Some microorganisms reside in the root nodules of leguminous plants. They can fix nitrogen from air into soil and increase the soil fertility.

Some bacteria present in the soil fix nitrogen from the atmosphere and convert into nitrogenous compounds. Certain bacteria convert compounds of nitrogen present in the soil into nitrogen gas which is released to the atmosphere.

Microorganisms: friend and foe class 8 Science Notes

Microorganisms are microscopic organisms that cannot be seen with the naked eye. These organisms are usually unicellular in nature.

Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae. Viruses are also microscopic but are different from other microorganisms.

Diseases like dysentery and malaria are caused by protozoa (protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.

Microorganisms may be single-celled like bacteria, some algae and protozoa, or multicellular, such as many algae and fungi. They live in all types of environment, ranging from ice cold climate to hot springs; and deserts to marshy lands. It is also found inside the bodies of animals including humans.

Class 8 Science Chapter 2 Microorganisms: friend and foe Questions Answers

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.

(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 and enhance fertility of soil.

(d) Cholera is caused by bacteria.

2. Tick the correct answer.

(a) Yeast is used in the production of

(i) sugar (ii) alcohol (iii) hydrochloric acid (iv) oxygen

Ans: alcohol

(b) The following is an antibiotic

(i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast

Ans: Streptomycin

(c) Carrier of malaria-causing protozoan is

(i) female Anopheles mosquito (ii) cockroach

(iii) housefly (iv) butterfly

Ans: female Anopheles mosquito

(d) The most common carrier of communicable diseases is

(i) ant (ii) housefly (iii) dragonfly (iv) spider

Ans: housefly

(e) The bread or idli dough rises because of

(i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading

Ans: 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: fermentation

NCERT Solutions of Microorganisms: friend and foe class 8 Science

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

Ans: A 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

4. Can microorganisms be seen with the naked eye ? If not, how can they be seen ?

Ans: Microorganisms cannot be seen by the naked eye because they are very small. They can be seen with the help of a microscope.

5. What are the major groups of microorganisms ?

Ans: Microorganisms are classified on the basis of their size into four major groups;

(a) Bacteria

(b) Fungi

(d) Algae

6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans: The microorganisms which can fix atmospheric nitrogen in the soil is rhizobium.

NCERT Solutions for Microorganisms: friend and foe class 8 Science

7. Write 10 lines on the usefulness of microorganisms in our lives.

Ans: Microorganisms are useful to us in many ways, 10 lines on the usefulness of microorganisms in our lives are;

(i) Microorganisms are helpful in cleaning up of the environment.

(ii) Microorganisms are helpful in producing vaccines against disease-causing agents.

(iii) Antibiotics are being produced from bacteria and fungi.

(iv) Bacteria like Lactobacillus convert milk into curd.

(v) Bacteria are also involved in the making of cheese, pickle etc.

(vi) Microorganisms are used for the large scale production of alcohol, wine and vinegar.

(vii) Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.

(viii) Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed.

(ix) Some bacteria fix atmospheric nitrogen and increase soil fertility.

(x) Microorganisms decompose dead organic waste of plants and animals to convert them into simple substances.

8. Write a short paragraph on the harmful effects of microorganisms.

Ans: Microorganisms are harmful to us in many ways. Microorganisms, called pathogens cause disease in humans, plants and animals. For example; Cholera in humans is caused by bacteria called Vibrio cholera. Common ailments like cold, flu, cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the cattle are also caused by viruses. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. This food-borne illness is called food poisoning. Some microorganisms spoil leather and clothes.

9. What are antibiotics ? What precautions must be taken while taking antibiotics ?

Ans: The medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics.

Antibiotics should be taken only on the advice of a qualified doctor. One must complete the course prescribed by the doctor. Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria.