Microorganisms: Friends and Foe| Worksheet Solutions| Class 8

Worksheet solutions for chapter: Microorganisms: Friends and Foe for class 8 are provided below.

(1)Write “T” against the sentences which are true and write “F” against the sentences which are false.

(i) Viruses are microorganisms.

(ii) Food can not preserved by using salt.

(iii) Microorganisms are responsible for maintaining the nitrogen in the atmosphere.

(iv) Air is not a mode of transmission of diseases.


(i) Viruses are microorganisms. T

(ii) Food can not preserved by using salt. F

(iii) Microorganisms are responsible for maintaining the nitrogen in the atmosphere. T

(iv) Air is not a mode of transmission of diseases. F


(2) Define communicable diseases. Give some example of it.


Those diseases which can be transferred or communicate by an infected person to a healthy person via air, water, food or with contact are known as communicable diseases.

Eg:- Cold spreads when tiny droplets of infected persons travel at the time of sneezing to healthy person via air.


(3) What are carriers? How they spread diseases among human?


Carriers are those insects and animals which carry microbes to the healthy persons. Eg:- Housefly and mosquitoes.

When these carriers sits on garbage or animal excreta pathogens stick to them. When these flies sit on the uncovered food they leave pathogens on food which makes healthy people sick when they eat food.

Anopheles, a female mosquito works as carrier of malaria. It injected the blood of infected person to the healthy person when sucks him.

Female Aedes mosquito acts as a carrier of dengue virus which breeds in water collected anywhere (in coolers, tyres, flower pot etc).


(4) What is food preservation? Name some food preservatives?


Food preservation is a process to prevent the growth of microorganisms in the food to store food for long time in usable condition.

Eg:- Sodium benzoate , Sodium metabisulphite, common salt, sugar, oil and vinegar


(5)Define nitrogen cycle and explain it.


Nitrogen cycle is a cycle in which atmospheric nitrogen remains more or less same.

Nitrogen can not be taken directly by plants and animals. Plants and animals can use only nitrogen compound. Bacteria and blue green algae of soil convert the atmospheric nitrogen and nitrogen waste of the dead plants and animals into nitrogenous compound. Some other bacteria convert some part of this compound to nitrogen gas which goes back into the atmosphere. Therefore, nitrogen presents in the atmosphere remains same.

Nitrogen cycle is described by a diagram below:-

Microorganisms-friends and foe,nitrogen cycle,NCERT,class 8


(6) Write a short note on diseases spread by microorganisms in plants.


There are some diseases which are spread by the microorganisms in plants. Citrus canker, rust of wheat are some of them diseases. These diseases are spread by bacteria, fungi and virus by air, seeds and insect. These diseases are tabulated below:-

Some common plant diseases caused by microorganisms

S N Plant Diseases Causative Microorganism Mode of transmission
1. Citrus canker Bacteria Air
2. Rust of wheat Fungi Air, seeds
3. Yellow vein mosaic of bhindi (Okra) Virus Insect


Choose the correct answers:-

(7) Pasteurised milk can be drink without boiling.  Yes /No


Yes, pasteurised milk can be drink without boiling.


(8) Microorganisms are

(i) single celled

(ii) multi celled.

(iii) Both


(iii) both


(9) Microorganisms can survive in

(i) cold areas

(ii) deserts

(iii) both


(iii) both


(10) Can taking antibiotics useful in cold or flu?


No, antibiotics are not useful in cold or flu. Antibiotics are useful in diseases caused by bacteria and fungi. Cold or flu is caused by viruses.

Helping Topics

Microorganisms: Friend and Foe

NCERT Solutions Class 8