Chapter 2 : Microorganisms : Friend and Foe

Choose the correct Answers :

Q1. Which of the following reproduces only inside a host cell?
(a) Bacteria    (b) Virus      (c) Amoeba        (d) Fungus.

Answer: (b) Virus

[ Viruses are non-living outside a host body and rely on the host cell's machinery to replicate, hence they reproduce only inside a living host cell.]

2. A disease in human beings caused by virus is _______.
(a) typhoid     (b) influenza    (c) dysentry   (d) cholera

Answer: (b) Influenza

[ Influenza (flu) is caused by a virus. Typhoid, dysentery, and cholera are bacterial diseases.]

3.Pathogenic micro-organisms present in host cells are killed by medicines called
(a) pain killer     (b) antibodies       (c) antibiotics     (d) vaccines

Answer: (c) antibiotics

[ Antibiotics are medicines that kill or stop the growth of pathogenic micro-organisms (like bacteria) inside the host.]

4.The two micro-organisms which live in symbiotic association in lichens are
(a) fungus and protozoa     (b) bacteria and protozoa
(c) alga and bacteria         (d) alga and fungus

Answer: (d) alga and fungus

[ Lichens show symbiotic association (mutually beneficial relationship) between an alga (which provides food) and a fungus (which provides shelter and water).]

5.The gas released during the preparation of bread is
(a) oxygen       (c) carbon dioxide        (b) nitrogen      (d) sulphur dioxide

Answer: (c) carbon dioxide

[ During bread preparation, yeast (a fungus) respires anaerobically and releases carbon dioxide gas, which causes the dough to rise.]

7.Paheli dug two pits, A and B, in her garden. In pit A, she put a polyhtene bag packed with some agricultural waste. In pit B, she dumped the same kind of waste but without packing it in a polythene bag. She, then covered both the pits with soil. What did she observe after a month?
(a) Waste in pit A degraded faster than that in pit B.
(b) Waste in pit B degraded faster than that in pit A.

(c) Waste in both pits degraded almost equally.
(d) Waste in both pits did not degrade at all.

Answer: (b) Waste in pit B degraded faster than that in pit A.

[ Polythene (plastic) is non-biodegradable and prevents air/moisture from reaching the waste in pit A, slowing degradation. Pit B allows microbes to act freely.]

VERY SHORT ANSWER QUESTIONS

8. Unscramble the jumbled words underlined in the following statements.
(a) Cells of our body produce santiidobe to fight pathogens.
(b) curbossulite is an air-borne disease caused by a bacterium.
(c) Xanrhat is a dangerous bacterial disease.
(d) Yeasts are used in the wine industry because of their property of meronettinaf.

Answer: (a) Cells of our body produce antibodies to fight pathogens.

(b) Tuberculosis is an air-borne disease caused by a bacterium.

(c) Anthrax is a dangerous bacterial disease.

(d) Yeasts are used in the wine industry because of their property of fermentation.

9. Suggest a suitable word for each of the following statements.
(a) Chemicals added to food to prevent growth of microorganisms.
(b) Nitrogen-fixing microorganism present in the root nodules of legumes.
(c) Agent which spreads pathogens from one place to another.
(d) Chemicals which kill or stop the growth of pathogens.

Answer: (a) Chemicals added to food to prevent growth of microorganisms. → Preservatives
(b) Nitrogen-fixing microorganism present in the root nodules of legumes. → Rhizobium
(c) Agent which spreads pathogens from one place to another. →  Carrier (Vector)
(d) Chemicals which kill or stop the growth of pathogens. → Antibiotics

10. Match the names of scientists given in Column A with the discovery made by them given in Column B.
     Column A                          Column B
(a) Louis Pasteur                    (i) Penicillin
(b) Robert Koch                     (ii) anthrax bacterium
(c) Edward Jenner                  (iii) Fermentation
(d) Alexander Fleming            (iv) small pox vaccine
                                            (v) Typhoid

Answer:  (a) Louis Pasteur → (iii) Fermentation
[ Louis Pasteur discovered the process of fermentation and also disproved spontaneous generation.]

(b) Robert Koch → (ii) anthrax bacterium
[ Robert Koch discovered the anthrax bacterium (Bacillus anthracis).]

(c) Edward Jenner → (iv) small pox vaccine
[ Edward Jenner developed the first smallpox vaccine using cowpox virus.]

(d) Alexander Fleming → (i) Penicillin
[ Alexander Fleming discovered the first antibiotic, penicillin, from the fungus Penicillium.]

11. Name one commercial use of yeast.

Answer: Yeast is used in the baking industry to make bread, cake, and pastries rise by producing carbon dioxide gas through fermentation.

12. Name the process in yeast that converts sugars into alcohol.

Answer: The process in yeast that converts sugars into alcohol is called fermentation. During fermentation, yeast breaks down sugar into alcohol (ethanol) and carbon dioxide in the absence of oxygen.

13. In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?

Answer: Blue-green algae (cyanobacteria) enrich the soil with nitrogen. They are nitrogen-fixing microorganisms that convert atmospheric nitrogen into forms usable by plants, thereby increasing soil fertility.

14. Why should we avoid standing close to a tuberculosis patient while he/she is coughing?

Answer: We should avoid standing close to a tuberculosis patient while coughing because TB spreads through air droplets released during coughing. Inhaling these droplets can infect a healthy person and cause tuberculosis infection in the lungs.

15. Polio drops are not given to children suffering from diarrhoea. Why?

Answer: Polio drops are not given to children suffering from diarrhoea because the medicine may pass out of the body too quickly without proper absorption. This reduces the effectiveness of the vaccine, so it is given after the child recovers.

16. Paheli watched her grandmother making mango pickle. After she bottled the pickle, her grand mother poured oil on top of the pickle before closing the lid. Paheli wanted to know why oil was poured? Can you help her understand why?

Answer: Oil is poured on top of the pickle to create a protective layer that prevents air (oxygen) and moisture from entering. This stops the growth of aerobic microorganisms (like fungi and bacteria) that would otherwise spoil the pickle, thus preserving it for a longer time.

SHORT ANSWER QUESTIONS

17. Match the microorganisms given in the Column A to the group to which they belong in Column B.
   Column A                 Column B
(a) Lactobacillus            (i) Algae
(b) Aspergillus              (ii) Protozoa
(c) Spirogyra                (iii) Fungi
(d) Paramecium           (iv) Bacteria

Answer: (a) Lactobacillus → (iv) Bacteria
[ Lactobacillus is a bacterium used in curd formation. ]

(b) Aspergillus → (iii) Fungi
[ Aspergillus is a fungus (mould) used in producing antibiotics like penicillin. ]

(c) Spirogyra → (i) Algae
[ Spirogyra is a green alga found in ponds. ]

(d) Paramecium → (ii) Protozoa
[ Paramecium is a unicellular protozoan.]

18. Classify the following into friendly and harmful microorganisms.
Yeast, malarial parasite, Lactobacillus, bread mould, Rhizobium, Bacillus anthracis
Friendly                 Harmful
________             ________
________             ________
________             ________
________             ________

Answer: The classification is :

Friendly	Harmful
Yeast	Malarial parasite
Lactobacillus	Bread mould
Rhizobium	Bacillus anthracis

19. While returning from the school, Boojho ate chaat from a street hawker. When he reached home, he felt ill and complained of stomach ache and fell ill. What could be the reason?

Answer: Boojho likely consumed food contaminated with disease-causing microorganisms (pathogens) like bacteria (e.g., Salmonella, E. coli) due to unhygienic handling of the chaat by the street hawker. This caused food poisoning or an infection, leading to stomach ache and illness.

20. What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left in the open for a day or two?

Answer: Pooris will turn stale and may develop a foul smell due to microbial growth. Unused kneaded flour will get fermented by airborne yeast and bacteria, producing a sour smell and cracks on the surface.

21. (a) Name two diseases that are caused by virus.
(b) Write one important characteristic of virus.

Answer: (a) Two diseases caused by virus are Influenza (flu) and Polio

(b) A virus reproduces only inside the living cells of a host organism and remains inactive outside.

LONG ANSWER QUESTIONS

22. Observe the Fig.2.1 and answer the questions that follows.

     

                        Fig. 2.1

(a) Write the name of the disease.
(b) Name the causative agent of this disease?
(c) How does the disease spread from one plant to another?
(d) Name any two plant diseases and the microbes that cause them.

Answer: (a) The name of the disease is Yellow vein mosaic of bhindi.

(b) The causative agent of this disease is a virus.

(c) The disease spreads from one plant to another through insects, such as whiteflies.

(d) Two plant diseases and their causative microbes are: Citrus canker (caused by bacteria) and Rust of wheat (caused by fungi).

23. How do vaccines work?

Answer: Vaccines contain weakened or dead germs. When injected into the body, they trigger the immune system to produce antibodies. These antibodies remain in the body and fight against the actual disease-causing germs if they enter later, thus providing immunity.

24. Observe the set up given in Fig. 2.2 and answer the following questions.
(a) What happens to the sugar solution in A?
(b) Which gas is released in A?
(c) What changes will you observe in B when the released gas passes through it?

 

                                      Fig. 2.2

Answer: (a) The sugar solution undergoes fermentation. The yeast converts the sugar into alcohol and releases carbon dioxide.

(b) The gas released is carbon dioxide.

(c) The lime water turns milky (cloudy). This is a standard test that confirms the presence of carbon dioxide.

25. Observe the Fig.2.3 and answer the following questions.

  

                   Fig. 2.3

(a) Name the microorganism and the group to which it belongs.
(b) Name the food item on which the organism grows.
(c) Does it grow well in dry or in moist conditions?
(d) Is it safe to eat infected bread?

Answer: (a) The microorganism is Rhizopus, and it belongs to the group Fungi.

(b) It grows on moist bread.

(c) It grows well in moist and warm conditions.

(d) No, it is not safe to eat infected bread because the mould can produce harmful toxins and its root-like structures (hyphae) spread deep inside the bread where they cannot be seen.

26. Give reasons for the following.
(a) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed without boiling.
(b) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside.
(c) Farmers prefer to grow beans and peas in nitrogen deficient soils.
(d) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?

Answer: (a) Fresh milk may contain harmful microorganisms (bacteria) that are killed by boiling. Processed milk (packet milk) is already pasteurized (heated to high temperature briefly) to kill pathogens, so it is safe to consume without boiling.

(b) Refrigerators slow down the growth of microorganisms on raw vegetables and fruits. Jams and pickles contain high sugar or salt and oil, which create a environment where microbes cannot grow easily, so they can be kept outside.

(c) Beans and peas are leguminous plants. They have root nodules containing Rhizobium bacteria that fix atmospheric nitrogen into the soil, enriching it naturally. Thus, they grow well even in nitrogen-deficient soils.

(d) Mosquitoes lay their eggs in stagnant water, and their larvae (young ones) develop and live in water before becoming adult mosquitoes. Preventing water stagnation stops their breeding cycle.

27. How can we prevent the following diseases?
(a) Cholera       (b) Typhoid        (c) Hepatitis A

Answer:  (a) Cholera can be prevented by drinking clean, boiled or chlorinated water, maintaining proper personal hygiene, washing hands before eating and consuming properly cooked food.

(b) Typhoid can be prevented by getting vaccinated, drinking safe water, avoiding street food, maintaining proper sanitation and washing hands thoroughly after using the toilet and before meals.

(c) Hepatitis A can be prevented by consuming clean water, avoiding contaminated food, maintaining good personal hygiene, washing fruits and vegetables properly and getting vaccinated.

28. Complete the following cycle given as Fig. 2.4 by filling the blanks
(a), (b), (c) (d)

                                        Fig. 2.4

Answer:  (a) Lightning .

(b) Nitrogen fixing bacteria fix atmospheric nitrogen.

(c) Nitrogenous waste from excretion and death .

(d) Bacteria turn compounds of nitrogen into gaseous nitrogen .