RBSE Solutions for Class 8 Science Chapter 2 Microorganisms: Friend and Foe

Rajasthan Board RBSE Solutions for Class 8 Science Chapter 2 Microorganisms: Friend and Foe Textbook Exercise Questions and Answers.

RBSE Class 8 Science Solutions Chapter 2 Microorganisms: Friend and Foe

RBSE Class 8 Science Microorganisms: Friend and Foe InText Questions and Answers

Page 21

Question 2. 
Why are children / infants given vaccination?
Answer:
Vaccination is used to protect the infants and children from diseases. 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 enters again. The antibodies remain for ever in our body and we are protected from the disease causing microbes. Several diseases, such as polio, cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

Page 23

Question 3. 
How do you prevent the spread of communicable diseases?
Answer:
We can prevent the spread of communicable diseases by keeping a handkerchief on the nose and mouth while sneezing. We can also prevent by keeping a distance from infected persons.

Question 4. 
Why does the teacher keep telling us not to let water collect anywhere in the neighbourhood?
 Answer:
 The teacher keeps telling us not to let water collect anywhere in the neighbourhood because almost all mosquitoes breed in water and multiply themselves. These mosquitoes spread serious diseases, hence we should keep surrounding clean to prevent breeding of mosquitoes.

Page 25

Question 5. 
Paheli wonders how can food become a 'poison'?
Answer:
Micro organism that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Page 26

Question 6. 
Why does the milk that comes in packets not spoil? My mother told me that the milk is 'pasteurised'. What is pasteurisation?
Answer:
Any liquid material, specially milk, is heated to about 70°C for 15 to 30 seconds and then suddenly chilled and stored. By doing, so it prevents the growth of microbes this process is called pasteurization.

RBSE Class 8 Science Microorganisms: Friend and Foe Textbook Questions and Answers 

Question 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) Microscope 
(b) Atmospheric Nitrogen 
(c) Yeast 
(d) Bacteria 

Question 2. 
Tick the correct answer:
(a) Yeast is used in the production of -
(i) sugar 
(ii) alcohol 
(iii) hydrochloric acid
(iv) oxygen

(b) The following is an antibiotic -
(i) Sodium bicarbonate 
(ii) Streptomycin 
(iii) Alcohol 
(iv) Yeast

(c) Carrier of malaria - causing protozoan is -
(i) female Anopheles mosquito 
(ii) cockroach
(iii) housefly 
(iv) butterfly

(d) The most common carrier of communicable diseases is -
(i) ant 
(ii) housefly 
(iii) dragonfly 
(iv) spider

(e) The bread or idli dough rises because of -
(i) heat 
(ii) grinding 
(iii) growth of yeast cells
(iv) kneading

(f) The process of conversion of sugar into alcohol is called -
(i) nitrogen fixation 
(ii) moulding 
(iii) fermentation 
(iv) infection
Answer:
(a) (ii) alcohol 
(b) (ii) streptomycin 
(c) (i) female Anopheles mosquito
(d) (ii) housefly 
(e) (iii) growth of yeast cells 
(f) (iii) fermentation

Question 3. 
Match the organisms in Column A with their action in Column B.

Answer:

Question 4. 
Can microorganisms be seen with the naked eye ? If not, how can they be seen? 
Answer:
Microorganisms can not be seen with naked eye. Some of these, such as fungus that grows on bread, can be seen with a magnifying lens while others can be seen with the help of microscope.

Question 5. 
What are the major groups of microorganisms?
Answer:
Microorganisms are classified into four major groups :

1. Bacteria 
2. Fungi 
3. Protozoa and 
4. some Algae. 

One other group is viruses. They are also microorganism but they are different from these microorganisms.

Question 6. 
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:

1. Rhizobium bacteria and 
2. Blue - green algae.

Question 7. 
Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
The uses of microorganisms in our lives are as follows:

1. Lactobacillus bacteria converts milk into curd.
2. Bacteria are also helpful in making cheese, pickles and many other food items.
3. Yeast is used in baking industry for making breads, pastries and cakes.
4. Microorganisms are used on a large scale in production of alcohol, wine and acetic acid.
5. Many antibiotics medicines are produced from bacteria and fungi.
6. Vaccins are made on a large scale from microorganisms.
7. Some bacteria and blue - green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. 
8. Microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.
9. Microorganisms play important role in making biogas and compost (manure).
10. In form of vaccine disease carrying microbes enters in our body, by this body produces antibodies.

Question 8. 
Write a short paragraph on the harmful effects of microorganisms.
Answer:
Harmful activities of microorganisms:

1. Some of the microorganisms cause diseases in human beings, plants and animals. Such diseases caused by microorganisms are called pathogens.
2. Some microorganisms spoil food, clothing and leather.
3. Many organisms cause disease in humans like - cholera, common cold, chicken pox and tuberculosis.
4. Bacteria also develop the disease in animals. For example, anthrax is a dangerous human and cattle disease caused by bacteria. Foot and mouth disease of cattle is caused by a virus.
5. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. Citrus canker is caused by bacteria. Fungi causes the rust of wheat and virus is responsible for yellow vein mosaic of bhindi.
6. Microorganisms that grow on our food sometimes produce toxic substances. These make food poisonous, causing serious illness and even death.

Question 9. 
What are antibiotics ? What precautions must be taken while taking antibiotics ?
Answer:
The medicines which kill or stop the growth of the disease causing microorganisms are called antibibtics. Streptomycin, tetracycline and erythromycin are some of the commonly used known antibiotics. These medicines are made from fungi and bacteria.
Precautions for using antibiotics :

1. Antibiotics should be taken only on the advice of a doctor.
2. The course of antibiotics medicine should be completed.
3. Unnecessarily antibiotics should not be used otherwise it may make the drug less effective when you might need in future. Inspite of this, antibiotics taken unnecessarily may kill the beneficial bacteria in the body.
4. Antibiotics are not effective against cold and flu.