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Question 1

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

Millions of organisms are present around us .They are so small and cannot be viewed with our naked eyes and can only be seen under a microscope. These are called microorganisms or microbes. (e.g.) bacteria and viruses. Microorganisms live almost everywhere – in the air, water, soil and even inside other organisms. Many live within our body. Some of them are useful while others are harmful and cause diseases in other living organisms.


Question 2

What are the major groups of microorganisms?

Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.


Question 3

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

Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses).


Question 4

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


Lacto bacillus is a bacteria that promotes the formation of cruds

Bacteria is also involved in the making of cheese

Yeast is used in the formation of alcohol and wine yeast converts the sugar into alcohol this process is called as fermentation

  • Making crud
  • Commercial use of micro organism
  • Antibiotics are medicines which kills the growth of disease causing micro organism
  • When disease causing microbes under our body he body produces antibodies which protects us from diseases this is how vaccines work
  • Increases soil fertility
  • Blue green algae are able to fix nitrogen from the atmosphere to enrich soil

Question 5

Write a short paragraph on the harms caused by microorganisms.

Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens

Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.

Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

There are some insects and animals which act as carriers of disease causing microbes

An example of a carrier is the female Anopheles mosquito which carries the parasite of malaria.

Disease— causing Microorganisms in Animals

Anthrax is a dangerous human and cattle disease caused by a bacterium

Food poisoning

Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances

Question 6

What are antibiotics? What precautions must be taken while taking Antibiotics?


Antibiotics are among the most frequently prescribed medications in modern medicine. Antibiotics cure disease by killing or injuring bacteria. The first antibiotic was penicillin, discovered accidentally from a mold culture. Today, over 100 different antibiotics are available to doctors to cure minor discomforts as well as life-threatening infections.

Although antibiotics are useful in a wide variety of infections, it is important to realize that antibiotics only treat bacterial infections. Antibiotics are useless against viral infections (for example, the common cold) and fungal infections

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