NCERT Class 8 Science Exemplar Chapter 2 - Microorganisms: Friend And Foe

Chapter 2 - Microorganisms: Friend And Foe

Multiple Choice Questions
Question 1: Which of the following reproduces only inside a host cell?
a) Bacteria
b) Virus
c) Amoeba
d) Fungus
Answer:
b) Virus

Question 2: A disease in human beings caused by virus is _______.
a) typhoid
b) influenza
c) dysentery
d) cholera
Answer:
b) influenza

Question 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

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

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

Question 6: The disease caused by a protozoan and spread by an insect is _________.
a) dengue
b) malaria
c) polio
d) measles
Answer:
b) malaria

Question 7: Paheli dug two pits, A and B, in her garden. In pit A, she put a polythene 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.

Very Short Answer Questions
Question 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.

Question 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) Preservatives
b) Carriers
c) Rhizobium
d) Antibiotics

Question 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 - Fermentation
b) Robert Koch - Anthrax bacterium
c) Edward Jenner - Small pox vaccine
d) Alexander Fleming - Penicillin

Question 11: Name one commercial use of yeast.
Answer:
Yeast is used to make alcohol, bread etc.

Question 12: Name the process in yeast that converts sugars into alcohol.
Answer:
The process in which the yeast converts sugars into alcohol is Fermentation.

Question 13: In the soil, which nutrient is enriched by blue-green algae (cyanobacteria)?
Answer:
Nitrogen is the nutrient in the soil which is enriched by blue-green algae.

Question 14: Why should we avoid standing close to a tuberculosis patient while he/she is coughing?
Answer:
Tuberculosis is an air-borne disease that is caused by bacteria which can easily spreads when the infected person coughs.

Question 15: Polio drops are not given to children suffering from diarrhoea. Why?
Answer:
Polio drops are not given to children suffering from diarrhoea because if he/she is suffering from diarrhoea, the orally given vaccine may be excreted out due to frequent motions.

Question 16: Paheli watched her grandmother making mango pickle. After she bottled the pickle, her grandmother 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:
Paheli’s grandmother poured oil on the top of the pickle before closing the lid because the use of oil prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

Short Answer Questions
Question 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 - Bacteria
b) Aspergillus - Fungi
c) Spirogyra - Algae
d) Paramecium - Protozoa

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

Friendly - Yeast, Lactobacillus, Rhizobium
Harmful - Malarial parasite, bread mould, bacillus anthracis

Question 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:
The main reason is that the chaat was contaminated by pathogenic microbes due to unhygienic conditions near the shop or the utensil used for serving could have contaminated.

Question 20: What will happen to ‘pooris’ and ‘unused kneaded flour’ if they are left in the open for a day or two?
Answer:
The ‘unused kneaded flour’, if left in warm conditions, gets infected by microbes which cause fermentation and spoils the flour. The pooris would remain in relatively good condition because they were deep fried in heated oil that kills microbes.

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

a) The two diseases that are caused by virus are Chicken Pox, Influenza.
b) Virus can reproduce only inside the cells of host.

Long Answer Questions
Question 22:
Observe the Fig.2.1 and answer the questions that follows.
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) Yellow vein mosaic of bhindi (Okra)
b) Virus
c) The disease spreads from one plant to another through insects.
d) The two plant diseases caused by microbes are
• Citrus Canker = Bacteria
• Rust of wheat = Fungi

Question 23: How do vaccines work?
Answer:
When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. If dead or weakened microbes are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease-causing microbes for ever. This is how a vaccine works.

Question 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?
Answer:

a) Yeast causes fermentation converting sugar into alcohol and carbon dioxide.
b) Carbon dioxide is released in A.
c) Lime water turns milky.

Question 25: Observe the Fig.2.3 and answer the following questions.
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 the bread mould. It belongs to fungi category.
b) It mainly grows on moist and stale bread.
c) It grows well in moist conditions.
d) No, it is not at all safe to eat the infected bread because the bread mould released few acids, which turn the normal bread into harmful one and changes its colour to blue-green.

Question 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 is boiled before consumption to kill the microorganisms present in it. But packed milk is pasteurised and does not contain any microorganisms and hence it can be consumed without boiling.
b) Raw vegetables and fruits get easily infected by microorganisms and get spoilt. They are kept in refrigerator as low temperature inhibits growth of microbes. Jams and pickles contain sugar and salt as preservatives. They do not get infected by microbes easily.
c) Beans and peas are leguminous plants and have Rhizobium bacterium in their root nodules. These bacteria can fix atmospheric nitrogen to enrich the soil with nitrogen and increase its fertility.
d) Though mosquitoes live on land, their larvae grow in water. If water stagnation is prevented the larvae cannot survive.

Question 27: How can we prevent the following diseases?
a) Cholera
b) Typhoid
c) Hepatitis A
Answer:

a) Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
b) Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
c) Drink boiled drinking water. Vaccination.

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

a) Lightning fixes nitrogen.
b) Nitrogen fixing bacteria and blue green algae fix atmospheric nitrogen.
c) Nitrogenous waste from excretion and death.
d) Bacteria turn compounds of nitrogen into gaseous nitrogen.

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