NCERT Exemplar Solution Class 8 Science Chapter 2

NCERT Exemplar Solution Class 8 Science Chapter 2

NCERT Exemplar Solution Class 8 Science Chapter 2 Micro-organisms: Friend and Foe all Questions Answer Solution. NCERT Exemplar Class 8 Science Chapter 2 Solution PDF.

NCERT Exemplar Solution Class 8 Science Chapter 2: Overview

NCERT Exemplar Solution Class 8 Science Chapter 2

Board

NCERT
Topic

Exemplar Problem Solution

Class

8
Subject

Science

Chapter

2
Chapter Name

Micro-organisms: Friend and Foe

NCERT Exemplar Solution Class 8 Science Chapter 2 Micro-organisms: Friend and Foe

Multiple Choice Questions

1) Which of the following reproduces only inside a host cell?

A)Bacteria

B)Virus

C)Amoeba

D)Fungus

Answer:- b) Virus

Virus reproduce inside the host cell. Other microorganisms does not reproduce inside the host cell.

2)A disease in human beings caused by virus is _____________.

A)Typhoid

B)Influenza

C)Dysentery

D)Cholera

Answer:- b) influenza

Typhoid and cholera is caused bacteria, while the dysentery is caused by protozoa but the Influenza is caused by virus.

3)Pathogenic microorganisms present in host cells are killed by medicines called

A)Pain killer

B)Antibodies

C)Antibiotics

D)Vaccines

Answer:- c) Antibiotics

Antibiotics are medicines which is  made up of microorganisms. Antibiotics kills or stop the growth of the pathogenic microorganisms.

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

These is an example of symbiotic association which shares their shelter and food. Alga and fungus live in symbiotic association in lichens.

5)The gas released during the preparation of bread is

A)Oxygen

B)Carbon dioxide

C)Nitrogen

D)Sulphur dioxide

Answer:- b) Carbon dioxide

Carbon dioxide is released during the preparation of bread because bread is formed by the process of fermentation of yeast.

6)The disease caused by a protozoa and spread by an insect is ________.

A)Dengue

B)Malaria

C)Polio

D)Measles

Answer:- b) Malaria

Malaria is the protozoa causing disease. Which is spread through insects. polio, measles Dengue is caused by virus.

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.

Waste in pit A is in the tightly packed polythene bag thus the growth of Microbes does not grow properly  and thus waste does not degraded. Waste in pit B is not tightly packed thus Microbes can attacked over it and the waste can be degraded faster.

Very Short Answer Questions

8) Unscramble the jumbled words underlined in the following statements.

A) Cells of our body produces santiidobefight pathogens.

Answer:-  Cells of our body produces Antibodies which fight pathogens.

B) Curbossuliteis an air – borne diseases caused by a bacterium.

Answer:-  Tuberculosis is an air- borne diseases caused by a bacterium.

C)Xanrahatis a dangerous bacterial disease.

Answer:- Anthrax is a dangerous bacterial disease.

D)Yeasts are used in the wine industry because of their property of meronettinaf.

Answer:- Yeats 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.

Answer:-  Preservatives

B)Nitrogen- fixing microorganisms present in the root nodules of legumes.

Answer:-  Rhizobium

C) Agent which spreads pathogens from one place to another.

Answer:- carrier/Vector

D) Chemicals which kill or stop the Growth of pathogens.

Answer:- Antibiotics

10) Match the names of the 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) Robertkoch                ii) anthrax bacterium

C) Edward Jenner          iii) Fermentation

D) Alexander Fleming    iv) small pox vaccine

v) Typhoid

Answer:-

a)Louis Pasteur → iii) Fermentation

b)Robert koch→  ii)  Anthrax bacterium

c)Edward Jenner→ iv) small pox vaccine

d)Alexander Fleming→ i) penicillin

11) Name one commercial use of yeast.

Answer:-

Yeast is commercially used in making bread in bakery. Yeast is mainly used for fermentation. The dough is fermented using yeast and then use for making breads.

One more commercial  use of yeast is making fermented alcohol.

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

Answer:- Fermentation is the process which convert the sugars into alcohol. Yeast is responsible for the conversion mechanism of sugar into alcohol and smell of it.

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

Answer:- Blue green algae i.e. cyanobacteria is responsible to fix the nitrogen in the soil. Which increases the soil fertility. These are also called as biological Nitrogen fixers.

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

Answer:- Tuberculosis is an bacterial disease. These disease is air borne. Which is spread through air when the patient of of tuberculosis (TB) coughs or sneezes in the open. The bacteria along with the saliva goes into air and inhaled by the other person and thus get infected by the TB.

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

Answer:-

Polio drops which is a vaccine are given to the children under 5yrs of age. These is a oral vaccine. The child suffering from the diarrhoea have the frequent motions. Thus the oral vaccine could be removed out and thus it will not work satisfactory.

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:- Salts and edible oils are generally used as the preservatives. These are used to check the growth of microorganisms. Adding salt or oil or any acid Preservatives to the pickle stops the microbes attacking on it. Adding lots of oil in pickle prevents from growing of bacteria or fungus on the pickle. Thus the pickle is prevented from the spoilage.

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

B) Aspergillus → iii) Fungi

C) Spirogyra → i) Algae

D) paramecium → ii) protozoa

18) Classify the following into friendly and harmful microorganisms.

Yeast, malarial parasite, Lactobacillus , bread mould , Rhizobium, Bacillus anthracis

Friendly                       Harmful

__________           _____________

__________            ______________

__________         ______________

__________         ______________

Answer:-

Friendly                          Harmful

Yeast            →     Malarial parasite

Lactobacillus        →    Bread mould

Rhizobium     →    Bacillus anthracis

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

Answer:-

Roadside chaat may be contaminated. As they are always in contact with the dirt and vehicles on the road. It may be attacked by the pathogens and Microbes due to unhygienic conditions. Also one reason may be the utensils used for serving chaat is contaminated. Due to these pathogens reached to the stomach and he fell ill and complained stomach ach.

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

Answer:- Unused kneaded flour if kept in open for one to two days then due towarm condition it may get infected by the microbes. Due to attack of microbes over it, fermentation occur and it spoils the dough of flour. It will smell foul after that. But in the condition of pooris, these are deep fried in heated oil which kills the microbes and remains comparatively fresh and good condition for longer time.

21) a) Name two diseases that are caused by virus.

Answer:-  polio, Influenza, chicken pox, measles, Hepatitis A, these are  some diseases that caused by virus.

b) write one important characteristics of virus.

Answer:- Virus are microorganism but these are different from other microorganisms. As they reproduce inside the host cell.

Long Answer Questions

22) Observe the fig. 2.1 and Answer the questions that follows.

Fig. 2.1

a) Write the names of the disease.

Answer:-  The disease which is shown in the figure is yellow vein mosaic of lady finger.     ( bhindi or okra)

b) Name the causative agent of this disease?

Answer:-  Viruses are the causative agent for the disease of yellow vein mosaic of lady finger.

c) How does the disease spread from one plant to Another?

Answer:- The causative agent of these disease is virus. It is spread from one plant to another plant through the insects.

d) Name any two plant diseases and the microbes that cause them.

Answer:- the plant diseases and the Microbes cause them are as follows –

Yellow vein mosaic of okra → Virus

Citrus canker → bacteria

Rust of wheat → Fungi

23) How do vaccines work?

Answer:-

If a disease causing microbes enters in the body, then the body produces Antibodies. Antibodies are the fighters of our body. These fight against the microbes. Whenever the Microbes enters the body the antibodies kills them. If dead and weak microbes are introduced into a healthy body, the body fight against the invading pathogen by producing antibodies. These Antibodies remains in the body forever and fight against the Microbes if enters in the body again. Thus the vaccine works on these principle.

24) Observe the set up given in fig. 2.2 and answer the following questions.

Fig. 2.2

A) What happens to the sugar solution in A ?

Answer:-  In the solution A, yeast convert the sugar into alcohol and carbon dioxide by the process of fermentation.

B) Which gas is released in A?

Answer:-  Carbon dioxide gas is released during the process of fermentation of alcohol in solution A.

C) What changes will you observe in B when the released gas passes through it?

Answer:- Changes observed in the figure B when the gas is passed through it, the lime water turns milky. The white coloured precipitation forms in the solution.

25) Observe the fig. 2.3 and answer the following questions.

Fig. 2.3

A) Name the microorganisms and the group to which it belongs.

Answer:- Micro-organisms shown in the figure is Fungus. Which is grown over the bread mould.

B) Name the food item on which the organisms grow.

Answer:- these microorganisms grow on moist bread Or knitted dough of flour.

C) Does it grow well in dry or in moist conditions?

Answer:- These are the fungus which grows in suitable moist conditions.

D) Is it safe to eat infected bread?

Answer:-  No. It is not safe to eat infected bread. The fungus attacked over it spoils the bread by producing the poisonous substance and these may cause worst effect on body.

26)Give reason for the following.

A) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed without boiling.

Answer:-Packed processed milk is pasteurised. It does not contain any microbes. Therefore it can be used without boiling. But fresh milk may contain microorganisms in it. Therefore boiling is necessary to kill them.

B) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside.

Answer:-  jams and pickles can be kept outsidebecause it contains sugar, salt or oils as Preservatives.Therefore it can be kept in open without refrigerators. But fresh fruits and raw vegetables can be easily attacked by the microbes and they can become spoil. If we kept it in refrigerators then the low temperature inhibits the growth of microbes. And thus the will comparatively remains fresh.

C) Farmers prefer to grow beans and peas in nitrogen deficient soils.

Answer:-

Peas and beans are the Leguminous plants which contains the Rhizobium bacteria in their roots nodules. These bacteria fixes the atmospheric nitrogen naturally in the soils . Which increases the soils nutrients naturally and thus increases the fertility of soil.

D) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why ?

Answer:-

mosquitoes flies in the air and live on land. But They bread on the water. Their larvae grow on water. If the water is stagnant then the larvae cannot survive and thus can control over the mosquitoes.

27) How can we prevent the following diseases?

A)Cholera

Answer:- Cholerais an bacterial disease, which is spread through water and food. To prevent the disease we can take prevention like –

Maintaining proper hygiene

Maintaining good sanitary habits

Consumption of proper boiled water

Consumption of properly cooked food

Vaccination.

B)Typhoid

Answer:- Typhoidis an bacteria causing disease. Which is spread through water. The prevention to be taken for these is to consume boiled water. Maintaining personal hygiene and keeping proper sanitary habits. And vaccination.

C)Hepatitis A

Answer:- hepatitis A is an virus causing disease. These disease is transmitted through water. The prevention to be takenfor these disease is drinking boiled water. And vaccination.

28) wing cycle given as fig. 2.4 filling the blanks (a), (b), (c), (d).

Fig. 2.4

Answer:-

Updated: April 22, 2021 — 3:00 pm

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