Microorganisms – Class 8th

A. Tick the correct answer:

1. Amoeba is a.

2.fungi cannot make their food because they lack.

3.Another name for algae.

4.Bacilli are______shaped bacteria.

5.formation of curd by milk is done by.

B. Fill in the blanks:

1.microorganisms can be seen with the help of

2._____ are smaller than the bacteria.

3. ______are unicellular organisms made up of a cell without a nucleus.

4. The unicellular organisms that sour milk curd are
Ans- lactobacillus

5._______and________are forms of protozoa.
Ans-Algae and Bacteria

6._______are plant-like organisms lacking chlorophyll.

7._____cause disease like ringworm and athlete’s foot.

C. Write T for true and F for false statements:

1. Rabies is a viral disease.

2. Mumps is caused by fungi.

3. Penicillin antibiotic is obtained from algae.

4. Sugar is not as a preservative in jams

5. Some algae help in nitrogen fixation.

D. Define the following terms:

Ans-Those small organisms which are not visible to naked eyes and can be seen under a microscope only.

2.Unicellular  organisms
Ans-Unicellular organisms are made up of a single cell.

Ans-Virus are smaller than the bacteria and are visible only under an electron microscope.

Ans-Protozoa is unicellular organisms that have animal-like characteristics. They can move from place to place.

E. Short answer questions:

  1. Name any three bacteria.
    Ans-Cocci, Bacilli and spiral. 

2. Name any two algae.
Ans-Red algae and Brown algae.

3. Name any two protozoa.
Ans-Giardia and Amoeba.

4. What does term protozoa mean?
Ans-The term protozoa mean first animals.

5. Name any two viruses.
Ans-Tobacco virus and Influenza virus.

6. How does salt prevent food spoilage?
Ans-Salt prevents food spoilage, which checks the growth of bacteria by forcing Microorganisms to lose water by a process called osmosis.

F. Long answer questions:

  1. How can bacteria prove to be harmful?
    Ans-(1) Bacteria cause spoilage of food like souring of milk, rotting of meat etc.
    (2)  Bacteria cause many fatal diseases like tuberculosis, tetanus, phenomenon, cholera, diphtheria etc.
    (3) Bacteria causes many diseases in the plant also. Many other diseases of fruit and vegetable are caused by bacteria.

2. How many kinds of algae are known yous? What are its uses?
Ans-Algae can be divided into three main types are red algae, brown algae and blue-green algae. Except for this three-colour, algae have much other colour combination like golden-brown algae etc.
(1) Algin is also obtained from marine algae which are used to manufacture medicines artificial fibre and shaving creams.
(2) The blue-green algae are used as bio fertilization.
(3) Some algae are seaweeds ate used as food in China and Japan
(4) Algae are also important for animal-like fish and snail, as they are algae as their food.
(5) Seaweeds are also used as fertilizers.

3. What are the uses and harms of protozoa?
Ans-(1) Protozoa feed algae and bacteria and, this form an important link between the aquatic food chain
(2) Protozoa decompose the organic waste into simpler nutrients which get back into the soil
(3) Some protozoa live in the digestive system of the animal and help in the digestion of cellulose.
(4) Parasitic protozoa cause s number of diseases in their hosts.
(5) Amoebic dysentery is caused by protozoa called entamoeba histolytica.
(6) Malaria is caused by bacteria called plasmodium

4. How is a virus different from other Microorganisms?
Ans-Virus are not living organisms as they do not have any cellular organization. They are lifeless until they enter any living organisms. They are smaller than any known cell. They can carry all living functions only when they enter a living cell, outside which they are totally non-living.


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