NCERT solution for class 8 // Science // Chapter 2 -- Microorganisms- friend or foe

 NCERT solutions > class 8  > science 


NCERT solution for class 8  // Science // Chapter 2  -- Microorganisms- friend or foe

Chapter 2  -- Microorganisms- friend or foe

Q1. Fill  in the blanks. 

1. Microorganisms can be seen with help of a microscope.

2. Blue green algae fix nitrogen directly from air and enhance fertility of soil.

3. Alcohol is produced with the help of yeast.

4. Cholera is caused by bacteria 

Q2. Tick the correct answer.

a) Yeast is used in production of 

i) Sugar ii) Alcohol.  iii) Hydrochloric acid. iv)  Oxygen

b ) The following is an antibiotic.

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

c) Carrier of malaria causing protozoan is

i) Female anopheles mosquito. ii) Cockroach

iii) Housefly.    iv) Butterfly.

d) The most common carrier of communicable disease is.

i) Ant    ii) House fly    iii ) Dragonfly   iv) Spider 

e) The bread for idli dough rises because of  

i ) Heat   ii) Grinding   iii) Growth of yeast cell  iv) Kneading

f) The process of conversion of sugar into alcohol is called  

 i ) Nitrogen fixation  ii) Molding  

  iii) Fermentation      iv) Infection.

Q3. Match the organism in column a with their action in column b

Column A.                                     Column B 

Bacteria.                           Fixing nitrogen

Rhizobium.                      Setting of curd 

Lactobacillus.                  Baking of bread 

Yeast                                 Causing malaria 

A protozoan.                     Causing cholera 

A virus                              Causing AIDS 

                                        Producing antibodies 

Ans - 

Column A.                                     Column B 

Bacteria.                              Causing cholera 

Rhizobium.                      Fixing nitrogen

Lactobacillus.                   Setting of curd 

Yeast                                 Baking of bread 

A protozoan.                    Causing malaria 

A virus                              Causing AIDS 

                                   

Q4 . Can microorganism be seen with the naked eyes if not how can they be seen.

Ans- No microorganism cannot be seen by naked eyes they can be seen with the help of microscope 

Q5 . What are the major groups of microorganisms.

Ans. -  There are five major groups of microorganisms 

  • Algae 
  • Fungi
  •  Protozoa 
  • Bacteria 
  • virus

Q6 . Name the microorganism which can fix atmospheric nitrogen in the soil.? 

Ans - Some member of bacteria and some member of algae fix atmospheric nitrogen in the soil 

Bacteria - Rhizobium 

Algae- Blue green algae 

Q7 . Write 10 lines on the usefulness of micro-organisms in our lives? 

Ans - Microorganism are very small in size we are unable to see them by naked eyes but they play the important role in plants and the environment.

Importance of microorganism

  • They are used in bakery industries to making different kind of food items like bread pizza toast etc.
  • Yeast is used to preparation of bravery industry for the alcoholic fermentation .
  • Lactobacillus bacteria is used in the formation of curd.
  • Microorganism are increases the soil fertility by fixing the atmospheric nitrogen example rhizobium blue green algae.
  • Microorganism are helpful in the preparation of antibiotics 
example penicillium 
  • Microorganisms helpful in the decomposition process so they clean the environment and reduce pollution.
  • Different kind of disease Vaccine is produced by the use of microorganism. 
  • Antibiotics made by the microorganism also helpful to control the plant disease

Q8 . Write a short paragraph on the harmful effect of the micro-organism.

Ans - Microorganism are also help harmful for plants in human in many ways.

  • Some microorganism causes disease in human being plants and animals that type of microorganism  are called pathogens.
  • Human - Maleria , Dengu , cholera etc 
  • Animal- Anthrax.
  • Plants - black wart in potato . Rust in wheat, citrus canker etc. 
  • Microorganisms spoil the food material and create food poisoning 

Q9. What are antibiotics ? What precautions must be taken while taking antibiotics. ? 

Ans - Antibiotics are the medicine which kill or stop the growth of disease or microorganism.

Eg - streptomycin ,Tetramycin, penicillium

Some precautions should be taken while taking antibiotics

  • Antibiotics must be avoided when not need
  • Antibiotics should be taken only on the advice of doctor ..
  • For the better result complete course of antibiotics is essential





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