NCERT Exemplar solutions for Science [English] Class 8 chapter 2 - Microorganisms : Friend and Foe [Latest edition]

Which of the following reproduces only inside a host cell?

A disease in human beings caused by virus is

Which of the following is a source of rayon?

Pathogenic micro-organisms present in host cells are killed by medicines called

The two micro-organisms which live in symbiotic association in lichens are

The gas released during the preparation of bread is

The disease caused by a protozoan and spread by an insect is ______.

Paheli dug two pits, A and B, in her garden. In pit A, she put a polythene bag packet with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month?

Unscramble the jumbled word underlined in the following statement.

Cells of our body produce santiidobe to fight pathogens. 

Unscramble the jumbled word underlined in the following statement.

Curbossulite is an air-borne disease caused by a bacterium. 

Unscramble the jumbled word underlined in the following statement.

Xanrhat is a dangerous bacterial disease. 

Unscramble the jumbled word underlined in the following statement.

Yeasts are used in the wine industry because of their property of meronettinaf. 

Suggest a suitable word for the following statement.

Chemicals added to food to prevent growth of microorganisms.

Suggest a suitable word for the following statement.

Nitrogen-fixing microorganism present in the root nodules of legumes.

Suggest a suitable word for the following statement.

Agent which spreads pathogens from one place to another.

Suggest a suitable word for the following statement.

Chemicals which kill or stop the growth of pathogens.

Match the names of scientists given in Column A with the discovery made by them given in Column B.

Name one commercial use of yeast.

Name the process in yeast that converts sugars into alcohol.

In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?

Why should we avoid standing dose to a tuberculosis patient while he/she is coughing?

Polio drops are not given to children suffering from diarrhoea. Why?

Paheli watched grandmother making mango pickle. After she bottled the pickle, her grandmother poured oil on top of the pickle before closing the lid. Paheli wanted to know why oil was poured? Can you help her understand why?

Match the microorganisms given in the Column A to the group to which they belong in Column B.

Classify the following into friendly and harmful microorganisms.

While returning from the school, Boojho ate chaat from a street hawker. When he reached home, he felt ill and complained of stomach ache and fell ill. What could be the reason? 

What will happen to ‘pooris’ and ‘unused kneaded flour' if they are left in the open for a day or two?

Name two diseases that are caused by virus.

Write one important characteristic of virus.

Observe the figure and answer the questions that follows.

1. Write the name of the disease.
2. Name the causative agent of this disease?
3. How does the disease spread from one plant to another?
4. Name any two plant diseases and the microbes that cause them.

How do vaccines work?

Observe the set-up given in figure and answer the following questions.

1. What happens to the sugar solution in A?
2. Which gas is released in A?
3. What changes will you observe in B when the released gas passes through it? 

Observe the figure and answer the following questions.

1. Name the microorganism and the group to which it belongs.
2. Name the food item on which the organism grows.
3. Does it grow well in dry or in moist conditions?
4. Is it safe to eat infected bread?

Give reason for the following.

Fresh milk is boiled before consumption while processed milk is stored in packets and can be consumed without boiling.

Give reason for the following.

Raw vegetables and fruits are kept in refrigerators, whereas jams and pickles can be kept outside.

Give reason for the following.

Farmers prefer to grow beans and peas in nitrogen deficient soils.

Give reason for the following.

Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?

How can we prevent the following diseases?

Cholera

How can we prevent the following diseases?

Typhoid

How can we prevent the following diseases?

Hepatitis-A

Complete the following cycle given as figure by filling the boxes (a), (b),(c), (d).