We have Provided the CBSE Solutions chapter-wise. Class 8 Science Chapter 2 Microorganisms Friend and Foe with Answers by expert subject teacher for latest syllabus and examination. Students can take a free CBSE Solutions of Microorganisms Friend and Foe. Each question has right answer Solved by Expert Teacher.
CBSE Solutions Class 8 Science Beehive Prose
Page No. 29
Exercise
Q1. 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) microscope.
(b) nitrogen
(c) yeast.
(d) bacteria.
Q2. Tick the correct answer:
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer: (ii) alcohol
(b) The following is an antibiotic
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
Answer: (ii) Streptomycin
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer: (i) female Anopheles mosquito
(d) The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
Answer: (ii) housefly
(e) The bread or idli dough rises because of
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading
Answer: (iii) 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: (iii) fermentation
Q3. Match the organisms in Column A with their action in Column B.
| A | B |
| (i) Bacteria (ii) Rhizobium (iii) Lactobacillus (iv) Yeast (v) A protozoan (vi) A virus | (a) Fixing nitrogen (b) Setting of curd (c) Baking of bread (d) Causing malaria (e) Causing cholera (f) Causing AIDS (g) Producing antibodies |
Answer:
| A | B |
| (i) Bacteria (ii) Rhizobium (iii) Lactobacillus (iv) Yeast (v) A protozoan (vi) A virus | (e) Causing cholera (a) Fixing nitrogen (b) Setting of curd (c) Baking of bread (d) Causing malaria (f) Causing AIDS |
Q4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer: The microorganisms cannot be seen with our naked eyes because they are very small in size. Some of these, such as fungus growing on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.
Q5. What are the major groups of microorganisms?
Answer: There are five major groups of microorganisms. They are enlisted as:
1) Bacteria:
- It is a single-celled organism.
- They can be spiral, rod-shaped, spherical-shaped, comma-shaped.
- It causes diseases like cholera, tuberculosis.
2) Fungi:
- Fungi are mostly multicellular organisms that cause several diseases.
- The moulds formed on bread are a type of fungi.
3) Protozoa:
- Protozoa can either be unicellular or multicellular.
- Amoeba and Plasmodium are examples of protozoa.
- They are harmful to humans as well as other organisms.
4) Virus:
- Viruses are disease-causing microorganisms that can only divide inside a host organism/cell.
- It can affect plants as well as animals or humans.
= HIV virus in humans and TMV virus in plants are examples of viruses.
5) Algae:
- They are the only microorganisms that are multicellular and have photosynthetic pigments.
- They are also known as precursors of plants.
- Spirogyra and Chlamydomonas are some examples of algae.
Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer: They are
- Rhizobium
- Azobhcter
- blue-green algae (such as Anabaena and Nostoc), etc.
Q7. Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
1) Lactobacillus is used to form curd from milk.
2) Rhizobium present in the roots of pulse plants fix nitrogen from air and supply nitrogen compounds to the pulse plants.
3) Microorganisms are also used in winemaking, baking, pickling, and other food making processes.
4) Alcoholic fermentation by yeast is widely used in the preparation of wine and bread.
5) 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.
6) Microbes also play an important role in the preparation of medicines. Antibiotics are chemicals produced by microorganisms to kill bacteria. Penicillin is an antibiotic made from Penicilium.
7) Bacteria present in our intestine helps in proper digestion and release Vitamin B which is absorbed by intestine.
8) Many vaccines are prepared from microorganisms. These vaccines are given to children to protect them from disease.
9) Certain microbes are also used in the biological treatment of sewage and industrial effluents.
10) Yeast is used in making idlis, bread, pastries and cakes.
Q8. 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 conditions gets spoilt by fungus, producing a white cotton-like growth on the bread.
Q9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer: Antibiotics are medicines produced by certain micro-organisms to kill other disease-causing micro-organisms.
Precautions to be taken while using antibiotics:
- Antibiotics should be taken under the supervision of a well qualified doctor.
- Course (intake) of antibiotics should be completed as per the prescription given by the doctor.
- 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 drugs may kill the useful bacteria present in our body.
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