In this post we will see class 8th science chapter 2 solution by expert teacher.
You can check the Complete Science Solution here – NCERT Class 8th Science Solutions – Complete Solution List
Chapter 2 Solutions
1. Fill in the blanks.
a) Microorganisms can be seen with the help of a _________.
(b) Blue green algae fix _________ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of _________.
(d) Cholera is caused by _________.
Answer –
(a) Microorganisms can be seen with the help of a _ microscope _.
(b) Blue green algae fix __ nitrogen _ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of _ yeast _.
(d) Cholera is caused by _ bacteria _.
2. Tick the correct answer.
(a)Yeast is the production of
(i) sugar (ii) alcohol
(iii) hydrochloric acid (iv) oxygen
Answer – Alcohol
(b) The following is an antibiotic
(i) sodium bicarbonate (ii) streptomycin
(iii) alcohol (iv) yeast
Answer – Streptomycin
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito (ii) cockroach
(iii) housefly (iv) butterfly
Answer – Female Anopheles mosquito
(d)The most common carrier of communicable diseases is
(i) ant (ii) housefly
(iii) Dragonfly (iv) spider
Answer – Housefly
(e)The bread or idli dough rises because of
(i) heat (ii) grinding
(iii) growth of yeast cells (iv) kneading
Answer – Growth of yeast cells
(f) The process of conversion of sugar into alcohol is called
(i) Nitrogen fixation (ii) Moulding
(iii) Fermentation (iv) Infection
Answer – Fermentation
3. Match the organisms in Column I with their action in Column II.
|
Column I |
Column II |
||
|
(i) |
Bacteria |
(a) |
Fixing nitrogen |
|
(ii) |
Rhizobium |
(b) |
Setting of curd |
|
(iii) |
Lactobacillus |
(c) |
Baking of bread |
|
(iv) |
Yeast |
(d) |
Causing malaria |
|
(v) |
A protozoan |
(e) |
Causing cholera |
|
(vi) |
A virus |
(f) |
Causing AIDS |
|
(g) |
Producing antibodies | ||
Answer –
|
Column I |
Column II |
||
|
(i) |
Bacteria |
(e) |
Causing cholera |
|
(ii) |
Rhizobium |
(a) |
Fixing nitrogen |
|
(iii) |
Lactobacillus |
(b) |
Setting of curd |
|
(iv) |
Yeast |
(c) |
Baking of bread |
|
(v) |
A protozoan |
(d) |
Causing malaria |
|
(vi) |
A virus |
(f) |
Causing AIDS |
4. Can microorganisms be seen with the naked eye? If not ,how can they be seen ?
Answer – Microorganisms are too small to be seen through naked eyes. They can be seen with the help of a magnifrying glass or a microscope. For example, fungue that grows on bread is so small that it can be seen only with the help of a magnifrying glass or microscope.
5. What are the major group of micro-organisms ?
Answer – There are five major groups of micro-organisms:
(i) Bacteria − They are single called disease – causing micro-organisms. They can be spiral or a rod- shaped.
(ii) Fungi − They are mostly multicellular disease-causing microbes. Bread moulds are common examples of fungi.
(iii) Protozoa − They mainly include organisms such as Amoeba, Plasmodium,etc. They can be unicellular or multicellular.
(iv) Algae − They include multicellular, photosynthetic organisms such as Spirogyra, Chlamydomonas, etc.
6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer – Bacteria such as rhizobium and certain blue – green algae present in the soil can be fix atmospheric nitrogen and convert it into usable nitrogenous compounds can be easily utilized by plant for the the synthesis of plant proteins and other compounds.
7. Write 10 lines on the usefulness of micro-organisms in our lives .
Answer – Micro-organisms are too small to be seen through naked eyes. However, they are vital to plants and the environment.
Importance of micro-organisms:
They are used in winemaking, baking, pickling, and other food making processes.
Alcoholic fermentation by yeast is widely used in the preparation of wine and bread. A bacterium Lactobacillus, promotes the formation of curd.
Microbes are used to reduce pollution . For example, decomposers such as bacteria and fungi break down dead bodies and excreta to form inorganic compounds, which can be absorbed by plants.
They are used to increase the soil fertility by fixing the atmospheric nitrogen with the help of bacterium Rhizobium and some other blue-green algae.
Microbes also play an important role in the preparation of medicines. Antibiotic are chemical produced by micro-organisms to kill bacteria. Streptomycin , for example is an antibiotic.
Certain microbes are also used in the biological treatment of sewage and industrial effluents.
8. Write a short paragraph on the harms caused by microorganisms.
Answer -Harmful effects of micro-organisms :
Micro-organisms cause diseases in animals. For example, in humans, bacteria cause diseases such as tuberculosis, cholera, typhoid, etc. In cattle, the foot and mouth disease is caused by a virus. Also, several microbes cause diseases in plants. For example, the productivity of wheat, orange, apple, etc. is reduced due to microbial diseases in plants. Certain microbes, on entering into our body, produce toxic substances. This leads to food poisoning. Some micro-organisms such as fungus spoil our food. For example, Bread when left unused under moist condition gets spoils by fungus, producing a white cotton – like growth on the bread.
9. What are antibiotics? What precautions must be taken while taking antibiotics ?
Answer – Antibiotics medicines produced by certain micro-organisms to kill other disease- causing microorganisms. These medicines are commonly obtained from bacteria and fungi, streptomycin, tetracycline, penicillin etc, are common antibiotics.
Precautions to be taken while using antibiotics:
(i) Antibiotics should taken under the supervision of a well qualified doctor.
(ii) Course (intake) of antibiotics should be completed as per the prescription given by the doctor.
(iii) Antibiotics should be taken in the right amount and at the right time. A wrong dose of antibiotics makes the drug ineffective. Also, excessive consumption of drug may kill the useful bacteria present in our body.
You can check the Complete Science Solution here – NCERT Class 8th Science Solutions – Complete Solution List
You can see other posts here,
- Class 8th NCERT Science Solution Chapter 15 – Some Natural Phenomena
- Class 8th NCERT Science Solution Chapter 14 – Chemical effects of electric current
- Class 8th NCERT Science Solution Chapter 13 – Sound
- Class 8th NCERT Science Solution Chapter 12 – Friction
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