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NCERT Solutions for class 8 Science Microorganisms: friend and foe

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Exercise

Q1: Fill in the blanks

  1. Microorganisms can be seen with the help of a microscope.
  2. Blue green algae fix nitrogen directly from air and enhance fertility of the soil.
  3. Alcohol is produced with the help of yeast.
  4. Cholera is caused by bacteria.

Q2: Tick the correct answer:

  1. Yeast is used in the production of

Ans: alcohol

  1. The following is an antibiotic

Ans: Streptomycin

  1. Carrier of malaria-causing protozoan is

Ans: female anopheles mosquito

  1. The most common carrier of communicable disease is

Ans: housefly

  1. The bread and idli dough rises because of

Ans: growth of yeast cell

  1. The process of conversion of sugar into alcohol in called

Ans: fermentation

Q3: Match the organisms in column A with their action in the column B.

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, producing antibodies

 

Q4: Can microorganisms be seen with the naked eye? If not, how can they be seen?

Ans: We cannot see microorganism with our naked eyes. In order, to see them we have to use microscope.

Q5: What are the major groups of microorganisms?

Ans: The major groups of microorganisms include the following:

  1. Bacteria
  2. Protozoa
  3. Algae
  4. Virus
  5. Fungi

Q6: Name the microorganisms, which can fix atmospheric nitrogen in the soil.

Ans: Blue green algae and Rhizobium are the microorganisms that can fix the atmospheric nitrogen in the soil.

Q7: Write 10 lines on the usefulness of microorganisms in our lives.

Ans: Microbes are useful in our life in the following 10 ways:

  1. Setting of curd
  2. Baking bread
  3. Producing vaccines
  4. Producing antibiotics
  5. Fixing the atmospheric nitrogen
  6. Cleaning the environment by decomposing waste material
  7. Helps in creating manure
  8. Increasing the fertility of the soil
  9. Producing of alcohol
  10. Helpful in bakery industries

Q8: Write a short paragraph on the harmful effects of microorganisms.

Ans: Some microorganisms are harmful and cause diseases in human, animals, and plants. These microorganisms are called pathogen. Microorganisms can be harmful in the following ways:

  1.  They can spoil the food.
  2. They can cause malaria, cholera or other diseases.
  3. They can cause infection in our body.
  4. A healthy may be infected from them easily.

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

Ans: Antibiotics are the medicines that are produced with help of friendly microbes. These antibiotics are used to cure bacterial diseases. A person should take antibiotic only after prescription from the physician or doctor because over dose of antibiotic may kill the friendly bacteria in our body.

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