Important questions Class VIII Science Chapter 2 Microorganisms - Friend and Foe

Fill in the blanks:

1. ___________ bacteria causes citrus canker.
2. ___________ is a skin disease in human caused by fungus.
3. The female Aedes mosquito is a carrier of the ________virus.
4. _______, ______ are chemicals that inhibit microbial growth.
5. When an antigen enters the body, the body produce proteins called ________ to destroy it.
6. A _________ is used to study microbes.
7. ________ is a unicellular fungus.
8. ________ made the first vaccine.
9. ________ microbe is present in our intestine as a friendly microbes.
10. ________ can kill disease causing microbes without causing injury to body.
11. _________ are on the borderline of living and non- living.
12. _______and ______ are two diseases caused by bacteria.
13. In legumes, the root nodules contain the bacterium_________.
14. Yeast is added to dough to produce _________which makes the dough rise.
15. The heating of milk upto to 70*C& then suddenly cooling is called _________.
1) Xanthomonas
2) Ringworm
3) Dengue
4) Sodium benzoate and sodium metabisulphite
5) Antibodies
6) Microbiology
7) Yeast
8) Edward Jenner
9) E.coli
10) antibiotics
11) viruses
12) cholera and Typhoid
13) Rhizobium
14) carbon di oxide
15) pasteurization


1. Name two parasitic protozoa that cause diseases in human?
Plasmodium ( Malaria), Amoeba ( Amoebic dysentery)
2. What are antibiotics?
Antibiotics can kill disease causing micro organism without causing any injury to body tissue or disturbance of the body functions. Examples: penicillin, ampicillin.
3. What is fermentation?
The process of conversion of sugar into acid or alcohol is called fermentation. Yeast is used to ferments sugar in grapes to make wine.
4. What is pasteurization? How is it useful?
Pasteurization of milk consists of heating it to high temperature of 70˚C for about n the flavor. This method was invented by Louis Pasteur.
5. What are vaccines? How does a vaccine work?
Vaccines consist of dead and weakened microbes. When these are swallowed or injected into the body of a patient, the body produces antibodies to fight them. The antibodies remain in the body and protect it from any future attack of disease germs.
6. Which microorganism acts as decomposers? How is this activity useful to us?
Microorganisms such as bacteria, fungi and protozoa help by decomposing the tissues of dead organisms to get their food. The nutrient that were taken from the soil by plants and animals and restored and are used again by living organisms.
7. Describe the role of Rhizobium in maintaining soil fertility?
Rhizobium bacteria are capable of converting the atmosphere nitrogen into nitrates and nitrites thereby increasing soil fertility.
8. What is communicable disease?
Diseases that spread from an infected person to healthy individual through air, water or direct contact is called communicable diseases.
9. Microbes will never grow food keep inside refrigerator? Do you agree why?
Rrefrigeration only delays but do not completely rule art the possibility of food spoilage. If the food is taken out of the freezer, the microbes start growing again.
10.Define- Food preservation and Food poisoning
Food preservation: Processing of food to prevent their spoilage and retain their nutritive value or long periods is called food preservation.
Food poisoning: Food has to be preserved for later use and should be kept fresh. If microbes grow on it the food gets spoilt and many cause food poisoning.

Practice Questions:

1. What is pathogen? How does it gain entry into the body of living organisms?
2. Why are bacteria and fungi said to be decomposers?
3. Give two ways in which bacteria are useful to us and two ways in which they are harmful?
4. Discuss five methods of food preservation?
5. Explain how microbes are useful to us?
6. Why are viruses considered to be the borderline between living and the non- living?
7. How do viruses cause diseases?
8. What is nitrogen cycle?
9. Which microorganism is used to make bread soft and fluffy? Discuss how this happens?
10. How does mosquito help in spreading microorganism?

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