CBSE Class 8 Science Micro Organisms Friends and Foe Assignment

A. Fill in the blanks

1.Microrganisms may be unicellular or ___
2. __ bacteria help to make curd from milk.
3. Disease causing microorganisms are called ___.
4.Ammonium salt in the soil is converted first into nitrites by____ bacteria.
5. The ability of one's body to resist a disease is called ___.
6. Salting draws out ___from food.
7. Nitrates in the soil are converted by __ bacteria into nitrogen gas.
8. The process of preventing food spoilage by chemical or physical methods is called food___.
Answer : 
1. multicellular       5. immunity
2.lactobacillus        6. water(moisture)
3.pathogens           7. pseudomonas
4.nitrosomonas       8. Preservation

ANSWER THE FOLLOWING QUESTIONS

B. Very short questions.

Q.1 Name any two antibiotics.
Answer : Streptomycin 2. Tetracycline

Q.2 Give the names of any two communicable diseases.
Answer : Common cold and chicken pox

Q.3 Name any two common diseases each that occur in plants and animals.
Answer : Plant disease – Citrus canker and Rust
Animal disease – Anthrax and bird flu

Q.4 Name two microbial diseases that spread through air.
Answer : Tuberculosis and Pneumonia

Q.5 What are microorganisms?
Answer : The organisms that cannot be seen with the naked eye and can only be observed through a microscope are called microorganisms.

Q.6 Name any disease caused by virus in humans.
Answer : Smallpox

C. Short Questions

Q.1 What is pasteurization?
Answer : Pasteurization is a process for preservation of milk. In this method, milk is heated at about 70°C for 15 to 30 seconds to kill the bacteria present in it and cooled quickly to 10º C to prevent the remaining bacteria from growing.

Q.2 How do legiuminous plants increase the soil fertility?
Answer : Rhizobium bacteria present in the root nodules of leguminous plants absorb nitrogen gas from the atmosphere and convert it into simple nitrogenous compound called nitrates. After harvesting , when the roots decompose, the nitrates present in the root nodules mix with the soil and enrich it with nitrogenous compounds and hence increase the soil fertility.

Q.3 What do you mean by nitrifying bacteria?
Answer : The bacterias that change nitrite into nitrate from ammonia or ammonium in nitrogen cycle are called nitrifying bacteria. Nitrosomonas, Nitrobacter are the nitrifying bacteria found in soil.

Q.4 How does female Anopheles mosquito spread malaria.
Answer : The female Anopheles mosquito sucks the blood of human beings. While sucking blood, it transmits plasmodium into human blood. Plasmodium causes malaria

Q.5 How do antibiotics work?
Answer : Antibiotics fight bacterial infections either by killing bacteria or slowing and suspending its growth. They do this by: attacking the wall or coating surrounding bacteria. Or by interfering with bacteria reproduction.

Q.6 (a) How do viruses differ from other microorganisms?
(b) What is meant by fermentation?
Answer : (a) 1. Viruses are microscopic organisms, generally very smaller than bacteria. They are parasitic in nature, i.e. they can thrive and reproduce only on the host cell like animals, bacteria and plants etc.
2.Viruses are non-living in nature until they come in contact with the living cells. Most of the viruses are infectious in nature. Whereas some of the other microorganisms are useful in nature. Viruses can multiply very rapidly than the microorganisms.
(b) The process of conversion of sugar into alcohol by the action of yeast is known as fermentation.

Q.7 What are communicable diseases? Name any two diseases each caused by viruses and bacteria.
Answer : Microbial diseases that are spread from an infected person to other healthy person through air, water, food, physical contact or by animals are called communicable diseases.
Two diseases caused by
Viruses - measles and AIDS
Bacteria-typhoid and cholera

Q.8 What is vaccine? How does it work?
Answer : A small dose of dead and weakened disease causing microbes used to stimulate immune response in the body is called vaccine.
When a vaccine is introduce in the body of a healthy person, it acts like a antigen . The body of the person produces antibodies against these introduced microbes. These antibodies remain in the body and protect him/her against future infections of the same microbe.

Q.9 Microorganisms decompose dead organic waste of plants and animals and help in keeping the environment clean.
(a) What would happen, if microorganisms do not perform this function?
(b) Being a student, how can you contribute in keeping the environment clean? Give two ways.
Answer : (a) If decomposers disappeared from a ecosystem, wastes as well as the remains of the dead organisms would pile up, and producers (plants) would not have enough nutrients.
(b) The two ways through which we can keep the environment clean –
(i) Reduce the usage of your electrical appliances.
(ii) Reduce usage of chemicals and pesticides.

D. LONG QUESTIONS

Q.1 Explain two methods of food preservation. Also, discuss the advantages of food preservation.
Answer : The two methods of food preservation are-
a. Chemical method
b. Preservation by sugars
(a) Chemical method :- Food can be preserved by using food preservatives like sodium benzoate, sodium metabisulphite etc.. Most chemicals preservatives prevent microbial growth by removing oxygen from the food items. Sodium benzoate is used for preserving fruit juices and squashes. Citric acid is used as a preservative in confectioneries.
(b) Preservation method :- Jams, jellies and squashes are preserved for a long time because of the presence of sugar in them. Sugar inhibits the growth of food - spoiling microorganisms by reducing the moisture content of the food.
Advantage of food preservation are –
(i) It decreases the wastage of food by avoiding spoilage.
(ii) It increases the storage period of food materials.
(iii) Nutritional value of the food is retained for a long period.
(iv) It ensures the availability of food at distant places and during the off season.

Q.2 Draw a neat diagram to show nitrogen cycle and explain the process of nitrification and denitrification.
Answer : (1) Nitrification–The conversion of ammonia into nitrates by nitrifying bacteria is called nitrification.
(2) Denitrification–The conversion of nitrates into free nitrogen gas by denitrifying bacteria (pseudomonas) is called denitrification.

Q.3 Describe the principal on which the following methods of food preservation are based:
(1) Boiling (2) Canning (3) Freezing (4) Dehydration
Answer : 1. Boiling. Boiling kills bacteria. So, boiling also helps in the preservation of liquid food like milk. Boiled milk can be preserved for 2-3 days, otherwise it goes sour within 8 to 10 hours.
2.Canning. Certain foodstuffs are kept in airtight time or containers. These containers keep away moisture and thus, help in preserving food for a longer time. Foods like fruits and fishes are boiled, sterilised and put into tins and closed airtight.
3. Freezing. Microbes such as fungi and bacteria cannot survive at very low temperature. So milk, eggs, and vegetables are preserved by keeping them in a refrigerator.
4.Dehydration. Dehydrayion means removal of water which is the key requirement of microbial growth from foodstuffs. So, pulses and grains are well dried and perserved. These are stored in moisture free places or vessels. Sun drying is a traditional method for preserving food.

More Questions

Q.1 Give one example of the following :

i) A unicellular algae
ii) A filamentous algae
iii) Algae forming clusters/colonies
iv) A brown algae
v) The bacteria found in curd
vi) One rod-shaped bacteria
vii) One spherical bacteria
viii) A protozoan which can photosynthesize

Q.2 Match the columns:

i) Entamoeba histolytica               a) Botulism
ii) Giardiasis                               b) Giardia
iii) Trypanosoma                         c) AIDS
iv) HIV                                       d) Curd
v) Yeast & lactobacillus                e) Amoebiasis
vi) Penicillium notatum                f) Sleeping sickness
vii) Streptococcus pneumonia      g) Antibiotic
viii) Clostridium botulinum           h) Pneumonia

Q.3 Write briefly about the following:

i) Diatoms ii) Mildew iii) Cyanobacteria iv) Zooplanktons v) Algal bloom
vi) Spores vii) Anaerobic bacteria viii) Binary fission ix) pasteurization x) Microbiology

Q.4 Answer the following questions:

a) List some methods of food preservation

b) Write two uses and two harms caused by the following :
i) Algae ii) Bacteria iii) Protozoa iv) Fungi

c) Draw well labelled diagram of the following :
i) Euglena ii) A bacterial cell iii) Paramecium

d) How do bacteria reproduce?

e) What is the major difference between bacterial cell and the cells of other organisms?

f) Why is “Virus” thought of as something in between the living and non-living ? How do they multiply within a host cell?

1.Microorganisms are found in
(A) Air, water and soil.
(B) Living and dead soil.
(C) Hot springs and ice-cold water.
(D) All of the above.

2.Alexander Fleming is associated with-
(A) Fermentation.
(B) Antibiotic Penicillin.
(C) Tetanus disease.
(D) Cork cells.

3.Fruit and fruit juices are often get spoiled due to fermentation. Microorganisms responsible for this are:
(A) Viruses.
(B) Protozoans.
(C) Yeasts.
(D) None of these.

4.Disease causing micro-organisms are:
(A) Bacteria.
(B) Viruses.
(C) Fungi.
(D) All of the above..

5.Micro-organisms are
(A) Harmful.
(B) Beneficial.
(C) Both (a) and (b).
(D) None of these.

6.Lactobacillus bacteria are responsible for the formation of:
(A) cake.
(B) curd.
(C) bread.
(D) pasteries.

7.Who discovered fermentation?
(A) Alexander Fleming.
(B) Edward Jenner.
(C) Louis Pasteur.
(D) Robert Koch.

8.High and low temperature
(A) inhibits the growth of microorganism.
(B) kills many microorganism.
(C) increase the growth of organism.
(D) Both (a) and (b).

9.Pathogens can enter our body through
(A) the air we breathe.
(B) the water we drink.
(C) the food we eat.
(D) All of the above.

10.The medicines which are made with the help of micro-organisms mainly fungi and bacteria and used to kill or stop the growth of the disease-causing micro-organisms are called as:
(A) Vaccines.
(B) Antibiotics.
(C) Antipyretic drugs.
(D) None of the above.

11.Female Aedes mosquito acts as carrier of:
(A) dengue virus.
(B) malaria parasite.
(C) chicken pox virus.
(D) polio virus.

12.The organism which are responsible for the conversion of sugar into alcohol is
(A) Viruses.
(B) Bacteria.
(C) Yeast.
(D) Protozoa.

13. Penicillin, streptomycin, tetracycline are the examples of
(A) Vaccines
(B) Antibiotics
(C) Antipyretic drugs
(D) None of the above

14.Micro-organism can cause food poisoning through:
(A) the air we breathe.
(B) the water we drink.
(C) the food we eat.
(D) All of the above.

15.Microorganisms are
(A) too small
(B) too big
(C) can be visible through naked eyes
(D) All of the above

16.The chemicals generally used to check the growth of microorganisms are called as:
(A) pasteurizers.
(B) preservatives.
(C) cleaners.
(D) fertilizers.

17.How much percentage of nitrogen gas are present in our atmosphere?
(A) 84%.
(B) 91%.
(C) 68%.
(D) 78%.

18.The programme in which pulse drops are given to the children is named as:
(A) Save Polio Programme.
(B) Help Polio Programme.
(C) Pulse Polio Programme.
(D) Check Polio Programme.

19.Microorganisms may be:
(A) unicellular.
(B) multicellular.
(C) Both (a) and (b).
(D) None of the above.

20.Dysentery and malaria caused by:
(A) Virus.
(B) Bacteria.
(C) Yeast.
(D) Protozoa.

21.Microorganism that shows the characteristic of both living and non-living is:
(A) Virus.
(B) Bacteria.
(C) Algae.
(D) Fungi.

22.Protozoans are very common and some of them cause serious diseases in human-beings such as:
(A) Malaria.
(B) Tuberculosis.
(C) None.
(D) Both (a) & (b).

23.Bite of female anopheles mosquito is harmful for human-beings, because
(A) it causes sleeping sickness.
(B) it acts as a carrier of malaria causing parasite.
(C) it causes itching all over the body.
(D) all of the above.

24.In vaccine microorganisms are used as:
(A) Live.
(B) Dead.
(C) Weakened.
(D) Both (b) and (c).

25.Small pox vaccine is discovered by:
(A) Alexander Fleming.
(B) Edward Jenner.
(C) Louis Pasteur.
(D) Robert Koch.

26.The bacteria responsible for the Anthrax disease:
(A) E.coli.
(B) Lactobacillus.
(C) Bacillus anthracis.
(D) Salmonella.

27.The bacterium Bacillus anthracis discovered by
(A) Alexander Fleming.
(B) Edward Jenner.
(C) Louis Pasteur.
(D) Robert Koch.

28.Sugar acts as preservative because it:
(A) increases the moisture content.
(B) reduce the moisture content.
(C) kills the microorganism.
(D) None of the above.

29.Milk is said to be pasteurized when it heated at
(A) At 90^o for 30 - 40 seconds
(B) At 70^o for 15 - 30 seconds
(C) At 80^o for 30 - 40 seconds
(D) At 50^o for 15 - 30 seconds

30.Nitrogen fixation is necessary because
(A) plants and animals are not be able to take atmospheric nitrogen directly.
(B) plants and animals are able to take atmospheric nitrogen directly.
(C) All of the above.
(D) None of the above.

31.Microorganisms play role in:
(A) increasing soil fertility.
(B) cleaning the environment.
(C) in fermentation.
(D) all of the above.

32.Yeast are widely used for making:
(A) curd.
(B) bread.
(C) cake.
(D) Both (b) & (c)

33.Which of the following disease is not considered as communicable disease.
(A) Cholera.
(B) Tuberculosis.
(C) Chicken pox.
(D) Cancer.

34.Which of the following organisms helps in nitrogen fixation.
(A) Bacteria.
(B) Blue green algae.
(C) Virus.
(D) Both (a) and (b).

35.Which of the following plant disease is caused by the bacteria.
(A) Citrus canker.
(B) Rust of wheat.
(C) Yellow vein mosaic of bhindi (okra).
(D) None of the above.

36.Which of the following plant disease is caused by the fungi.
(A) Citrus canker.
(B) Rust of wheat.
(C) Yellow vein mosaic of bhindi (okra).
(D) None of the above.

37.Which of the following plant disease is caused by the virus.
(A) Citrus canker.
(B) Rust of wheat.
(C) Yellow vein mosaic of bhindi (okra).
(D) None of the above.

38.Foot and mouth disease of cattle is caused by:
(A) Virus.
(B) Bacteria.
(C) Yeast.
(D) Protozoa.

39.Microorganisms decompose the plants, animal waste and converted them into:
(A) new organism.
(B) manure.
(C) medicine.
(D) None of the above.

40.Hepatitis-B can be caused by
(A) virus.
(B) bacteria.
(C) yeast.
(D) protozoa.

41.Who discovered the fermentation?

42.What do you understand by microorganisms?

43.Mention two important uses of fungi.

44.In which form microorganisms are used in vaccine?

45.Who discovered the vaccine for small pox?

46.Which bacteria is responsible for Anhrax disease?

47.Can we find a place without microbes in nature?

48.Which microorganism is used in the production of alcohol?

49.Name any two food items that are prepared using yeast.

50.Name any three habitats of microorganisms.

51.Name the bacteria which involved in the fixation of nitrogen in leguminous plants?

52.Name the bacteria which is responsible for the formation of curd?

53.Microorganisms can be seen with the help of a ______________

54.Blue green algae fix directly from air to enhance fertility of soil.

55.Alcohol Is produced with the help of ___________

56.Cholera is caused by

57.Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen

58.The following is an antibiotic
(1) Sodiumbicarbonate
(ti) Streptomycin
(ill) Alcohol
(tv) Yeast

59.Carrier of malaria-causing protozoan is
(1) Female Anopheles mosquito
(li) cockroach
(iii) housefly
(iv) butterfly

60.The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider

61.The bread or idli dough rises because of
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading

62.The process of conversion of sugar into alcohol is called
(i) nitrogen fixation
(ii) moulding
(ill) fermentation
(iv) infection

63.Explain how does blue-green algae help in increasing the fertility of soil.<

64.Name the insects, which carry the parasite of malaria and dengue?

65.What is to be called as preservatives?

66.Define pasteurization?

67.Why generally dry fruits and even vegetables are sold in sealed air tight packets?

68.What are the causes of food poisoning?

69.What do you mean by fermentation?

70.What are communicable diseases? Name some of them.

71.What are the major groups of microorganisms?<

72.Name the microorganisms which can fix atmospheric nitrogen In the soil

73.Write 10 Items on the usefulness of microorganisms in our lives.

74.Write a short paragraph on the harms caused by microorganisms.

75.What are antibiotics? What precautions must be taken while taking antibiotics?

76.Mention the causative organism and mode of transmission of these organisms in the following diseases.
(i) Tuberculosis
(ii) Polio
(iii) Malaria
(iv) Typhoid
(v) Hepatitis B
(vi Chicken Pox.

77.Explain Antibiotics in brief with the help of examples.

78.What is nitrogen fixation. Which organisms are able to fix atmospheric nitrogen.

79.Draw a diagram of
(i) Amoeba
(ii) Paramecium

80.What are pathogens? How can they enter in our body?

81.Describe the role of sugar, oil and vinegar in preservation of food?

82.What are the affects caused by disease causing microorganisms? How are they controlled and name some plant diseases with their causative organism.

83.How can High and low temperature affects the growth of microorganisms? <

84.Describe the useful and harmful effects of microorganisms?

85.State some beneficial effects of bacteria.

86.What do you understand by vaccine? Explain in detail?

87.Draw a well labeled diagram of nitrogen cycle?

6. Name two groups of micro-organisms live in colonies.

7. Name the micro-organism which promote the formation of curd.

8.What is fermentation?

9.Name the scientist who discovered the fermentation?

10.Who discovered the antibiotics ?

11. Name some antibiotic.

12.Name two communicable diseases.

13.Name the most popular vaccination programme.

14.Who discovered the vaccine for small pox.

15. Name two communicable diseases.

16.Name some preservatives.

17.Which microorganisms are called nitrogen fixing bacteria.

18.What are preservative?

19.Where does Rhizobium bacteria commonly live?

20.Name the carrier of dengue fever.

21.. Mention the amount of nitrogen gas in atmosphere ?