Q. 1. Into how many groups are microorganisms classified ?

Ans. Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae. But viruses are also microscopic.


Q. 2. Write a short note on viruses.

Ans. Viruses are microscopic in size. They reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses.


Q. 3. What are microorganisms ?

Ans. The living organisms aound us which we normally cannot see. These are called microorganisms or microbes.


Q. 4. What are the uses of micro-organisms ?

Ans. Microorganisms are used for various purposes—
(1) They are used in the preparation of curd, bread and cake.
(2) They are used in cleaning up of the environment, e.g., the organic wastes like vegetable peels, remains of animals, faeces, etc. are broken down into harmless and usable substances by bacteria.
(3) Infact, microorganisms have been used for the production of alcohol since ages.
(4) Bacteria are used in the preparation of medicines.
(5) In agriculture bacteria are used to increase the fertility of soil by fixing nitrogen.
(6) Curd contains several micro-organisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
(7) Bacteria are also involved in the making of cheese, pickles and many other food items.
(8) Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. That is why yeast is used in the baking industry for making breads, pastries and cakes.
(9) Some microorganisms are used as preservatives in food items.
(10) Microorganisms are used to prepare vaccines.


Q. 5. Match the organisms in column I with their action in column II.

    Column I   Column II
  (i) Bacteria (a) Fixing nitrogen
  (ii) Rhizobium (b) Setting of curd
  (iii) Lactobacillus (c) Baking of bread
  (iv) Yeast (d) Causing Malaria
  (v) A protozoan (e) Causing Cholera
  (vi) A virus (f) Causing AIDS
      (g) Producing antibodies
Ans.   Column I   Column II
  (i) Bacteria (a) Causing Cholera
  (ii) Rhizobium (b) Fixing nitrogen
  (iii) Lactobacillus (c) Setting of curd
  (iv) Yeast (d) Baking of bread
  (v) A protozoan (e) Causing Malaria
  (vi) A virus (f) Causing AIDS



Q. 6. Write a short paragraph on the harms caused by microorganisms.

Ans. Some microorganisms harm us in various ways. Many organisms cause diseases. Disease causing microorganisms are called pathogens. Ailments like cold, influenza (flu) and most coughs are caused by viruses and even foot and mouth disease of cattle is also caused to virus. Serious diseases like, chicken pox and polio are also caused by viruses. Diseases like dysentery and malaria are caused by protozoan. Some bacteria cause typhoid and tuberculosis (TB) anthrax, a dangerous human and cattle disease, is also caused by a bacteria. Some microorganisms spoil leather items and wooden-work. Apart from these harmful effects, some microorganisms release toxic substances when grow on food items. Thus we see that microorganisms harm us in many ways.


Q. 7. Is it true that microbes are essential part of our life ?

Ans. Microbes are no doubt essential parts of our life. Infact our important organs like nose, throat, mouth, and intestines are inhabitated by a large number of microbes. Apart from this, microorganisms help us in many ways directly or indirectly, like if decomposer microorganisms were not there, our forests would have become storehouse of dead plant and animal bodies and would have thus become unfit to support wildlife.


Q. 8. How are fungi harmful to us ?

Ans. Fungi harm us in the following ways :
(1) They are responsible for rottening of fruits and other edible vegetables.
(2) Some fungi serious diseases like ring worm.
(3) They spoil of bread, food and food products.
(4) Rotting of clothes, shoes and wooden furniture items is also caused by fungi.
(5) They cause diseases, specially skin diseases and ear infectious.


Q. 9. Fill in the blanks :
(1) Microorganisms can be seen with the help of a .......................... .
(2) Blue green algae fix .......................... directly from air to enhance fertility of soil.
(3) Alcohol is produced with the help of .......................... .
(4) Cholera is caused by a .......................... .

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


Q. 10. Coci bacteria are ...................... in shape. (a) round, (b) spiral, (c) comma and (d) rod.

Ans. (a) round.


Q. 11. Which bacteria are present in root nodules of the pear plant ?
(a) Plasmodium, (b) Coli, (c) Lactobacillus and (d) Rhizobium.

Ans. (d) Rhizobium.


Q. 12. How does food poisoning occur ? Name some microorganisms responsible for food poisoning.

Ans. In case food is not preserved properly, it leads to food poisoning. Bacteria and fungi are responsible for food poisoning.
Example : Baderia—Salmonella and Clostridium. Fungi—Moulds like Penicillium and Aspergillus.


Q. 13. How can the spoilage in food detected ?

Ans. We can detect the spoilage in food in the following ways :
(1) Odour. The food spoiled by bacteria emits repulsive smell. The bacteria break the proteins found in food. This is called putrefaction.
(2) Sourness. Generally the cooked food starts tasting sour. It is due to the production of acids by the action of certain bacteria, e.g., milk starts tasting sour if not preserved properly.
(3) Discolouration. Growth of microbes on food results in discolouration of food black. Moulds on breads, blue green moulds on citrus fruits and cheese cause the change in the original colour of the food. Any small discolouration indicates that the food has been spoiled and is unfit for consumption.
(4) Sliminess. Sometimes the food became slimy. It is also due to action of certain bacteria thread like slimes are also caused due to moulds. Thus we came to know that the food has been spoilt.