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class VIII

Key Concepts

algae, antibodies, antibiotics, bacteria, carrier, communicable disease, fermentation, fungi, lactobacillus, microorganism, nitrogen cycle, nitrogen fixation, pasteurization, pathogen, preservation, protozoa, rhizobium, vaccine, virus, yeast

essential questions

1. How do bacteria and viruses and protozoa look like?
2. Are all microorganisms harmful?
3. How have humans been able to use the micro organisms for their benefits?


  1. Define two micro organisms. Name any two micro organisms
  2. Define fermentation.
  3. Name the bacteria involved in fermentation of food.
  4. Write a short note on communicable diseases.
  5. Which of the following reproduces only inside a host cell?  a) bacteria  b) virus  c) amoeba   d) fungus
  6. Pathogenic microorganisms present in host cells are killed by medicines called  a) pain killer  b) antibodies  c) antibiotics   d) vaccines
  7. Yeast is used in the production of : a) alcohol    b) sugar   c) hydrochloric acid   d) oxygen
  8. The following is an antibiotic: a) sodium bicarbonate  b) streptomycin  c) alcohol    d) yeast
  9. Carrier of malaria- causing protozoan is: a) female anopheles mosquito   b) cockroach   c) Housefly    d) butterfly
  10. The most common carrier of communicable diseases is: a) ant     b) Housefly     c) dragonfly   d) spider
  11. The bread or idli dough rises because of : a) heat    b) grinding   c) growth of yeast cells    d) kneading
  12. The process of conversion of sugar into alcohol is called:  a) nitrogen fixation   b) molding   c) fermentation   d) infection
  13. Tuberculosis is caused by:  a) bacteria   b) fungi   c) protozoa  d) virus
  14. Measles and chicken pox is caused by:  a) bacteria   b) fungi   c) protozoa   d) virus
  15. Hepatitis A and Polio are caused by:  a) bacteria    b) fungi   c) protozoa   d) virus
  16. Which of the following terms is given to the microorganism that cause disease: a) antigens   b)  antibodies  c) pathogens  d) vectors
  17. The two microorganisms which live in symbiotic association in lichens are:  a) fungus and protozoa  b) algae and bacteria   c) bacteria and protozoa   d) algae and fungus
  18. Malaria is caused by:  a) bacteria  b) fungi   c) protozoa  d) virus
  19. Which bacteria leads to the curdling of milk: a) plasmodium    b) salmonella   c) lactobacillus  d) clostridium
  20. Which of the following helps in nitrogen fixation:  a) plasmodium  b) salmonella   c) lactobacillus   d) clostridium
  21. Which of the following bacteria resides n root nodules of leguminous plants: a) Rhizobium   b) salmonella   c) lactobacillus  d) clostridium
  22. Which of the following is a plant disease: a) citrus canker   b) anthrax   c) foot and mouth   d) measles
  23. Which of the following is animal disease in cattle: a) citrus canker  b) antharx   c) malaria  d) measles
  24. Which of the following is not a bacterium: a) plasmodium   b) lactobacillus   c) streptococcus   d) rhizobium
  25. Who discovered small pox vaccine: a) Alexander Flemming    b) Edward Jenner    c) Robert Koch    d) Watson
  26. Who discovered penicillin: a) Alexander Flemming   b) Edward Jenner    c) Robert Koch  d) Watson
  27. Carrier of dengue fever is:  a) housefly    b) anopheles mosquito   c) culex mosqito   d) flea
  28. Which of the following microorganisms are used in making antibiotic:  a) viruses   b) fungi   c) bacteria   d)  both a and c
  29. Match the following:

bacteria             a) Fixing nitrogen

rhizobium         b) setting of curd

lactobacillus     c) Baking of bread

yeast                  d) causing malaria

protozoan         e) causing AIDS

virus                 f) producing anti bodies

Match the following:

bacteria            i) yellow vein mosaic

fungi                 ii) citrus canker

virus                 iii) baking of bread

yeast                 iv) Rust of wheat

Match the following:

sodium benzoate      i) medicine

vaccine                       ii) nitrogen fixer

antibiotics                 iii) preservative

blue green algae      iv) inactive microbes



  1. What is the difference between viruses and other micro organisms.
  2. What are antibiotics? How are they made? Give two examples
  3. Why is it advised not to take antibiotics without doctors advise.
  4. How do vaccination prevent diseases?
  5. Write difference between harmful and friendly micro organisms.
  6. How can communicable diseases be prevented. Write 2 ways.
  7. How is food poisoning caused?
  8. Explain nitrogen cycle with diagram.
  9. What is the significance of crop rotation?
  10. Write the various ways in which the preservation of food takes place?
  11. Which of the following statements describes bacteriophage correctly: a) it it a bacterium which causes diseases in plants   b) it is a type of virus which attacks bacteria   c) it is a bacterium which kills viruses   d) it can multiply inside both living and non living cells
  12. Fungi reproduces by: a) fission  b) fusion  c) seed formation  d) spore formation
  13. Which of the following characteristics places algae in the group of autotroph: a) carrying out anaerobic respiration   b) manufacturing their own food  c) feeding on dead organisms  d) feeding on their organisms
  14. Which of the following enzymes is secreted by bacteria that can digest  cellulose: a) amylase  b) cellulose  c) lipase  d) protease
  15. Which of the following is/ are the functions performed by the microorganisms in the filed of biotechnology: a) production of bio plastic  b) production of hormones  c) gene therapy  d)  both B and C
  16. What helps in differentiating ‘ Spirogyra’ from  ‘ paramecium’:  a) mitochondria  b) Golgi bodies  c) nucleus  d) plastids
  17. the gas released during the preparation of breads is: a) oxygen  b) carbon dioxide  c) nitrogen  d) sulphur dioxide
  18. Which of the following organisms can perform photosynthesis: a) euglena   b) paramecium  c) mucor  d) mushroom
  19. Which of the following is the smallest microorganisms: a) algae   b) bacterium  c) protozoan  d) virus


  1. Why does the adding of yeast in the dough make the dough rise?
  2. Why is yeast used extensively in the fermentation industry?
  3. Why are children and infants given vaccination?
  4. Why do we use sugar for preserving food?
  5. Why is it important to store dry food items in air tight packets?
  6. Why is common salt used extensively in the preservation industry?
  7. Which of the following is represented by X in the figure given below: a) protozoan  b) bacteria  c) viruses  d)  algae
  8. A microorganism X is used in the making of bread. It is also used in making  which of the following substances: a) cheese   b) vinegar   c) wine    d) yoghurt
  9. What process takes place when yeast is added to grape juice and left for week: a) decomposition  b) fermentation  c) distillation  d)  oxidation
  10. The moist bread becomes moldy after a few days when it is left in a container with a cover. Which of the following conditions favor the growth of the fungus: a) absence of light  b) absence of water  c) presence of sunlight   d) presence of carbon di oxide
  11. Which of the following microorganisms play an important role in maintaining the balance of nitrogen gas in the atmosphere: a) virus  b) protozoan  c) bacteria  d)  algae
  12. What causes the dough to rise when yeast is added to it: a) increase in temperature  b) increase in the amount of substance   c)  an increase in the amount of released water by yeast cells  d) release of carbon di oxide gas



  1. Why do you think nitrogen cycle a very important process for farmers?
  2. Paheli wants to know the incorrect statements, given by her teacher as home-work?  i) sodium chloride prevents microbial infection in food.  ii)  rhizobium may be called beneficial protozoa iii) vector are the agents for killing the microbes.  : a) only i   b) only ii   c) only ii and iii  d) only i and iii
  3. Paheli wants to pick out the incorrect sentences from the given statements: a) foot and mouth disease is caused in human by a virus  b)  rust of wheat is a bacterial disease in plants  c) yellow vein mosaic of bhindi okra is a fungal disease in plants  Choose the correct option: a) only a and b    b) only b and c   c) all of the above   d) none of the above
  4. The precaution is observed in the use of antibiotics. Choose the incorrect sentence(s): a)  antibiotic may kill the useful bacteria in the body and harm us.   b) wrong dose of antibiotics makes the antibiotic less effective.  c) antibiotics should be taken only on the advice of perfect doctor.   d) none of the above
  5. Consider the given statements. Choose, which of the following statement is or are correct? 1)  hemocyanin and streptomycin are the antibiotics.  2)  antibiotics are not effective against disease caused by virus.   3) antibiotics are not effective to control disease in plants and animals.  4) all the above
  6. Paheli and Boojho discussed a topic of microorganisms. Choose which of the following statements is or are correct? 1)  a dilute solution of acetic acid is called vinegar.   2) acetobacter bacteria convert alcohol into acetic acid.  3) yeast is capable of converting sugar into alcohol. 4)  none of the above.   a) only 1  b) only 2  c) only 1 and 2  d) all of the above
  7. Boojho wants to know which of the following is correct: 1. Housefly carries the disease causing microbes inside its body   2. Mosquito  carries microbes inside its body  3. Anepholese mosquito carries plasmodium bacteria of  malaria. choose the correct option: a) only 1   b) only 2   c) both 2 and3  d) all of the above
  8. Find the connection between the following analogy between these micro organisms : a) typhoid: ___:: malaria:___   b) chicken pox: ___:: tuberculosis:____    c) rust of wheat: ____:: blue green algae:____