Class 8 - Science - CH2 - MIICROORGANISMS : FRIEND AND FOE

NCERT Chapter Solution and other Q & A

Virus
(source:openclipart)

Q1. Fill in the blanks:

Answer:
(a) Microorganisms can be seen with the help of a microscope.
(b) Blue-green algae fix nitrogen directly from air to enhance the fertility of the soil.
(c) Alcohol is produced with the help of yeast.
(d) Cholera is caused by Bacteria.

Q2. Tick the correct answer:
(a) Yeast is used in 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) the 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

Q3. Match the organisms in Column I with their action in Column II.

Column I	Column II
(i) Bacteria	(a) Fixing Nitrogen
(ii) RhizobiumÂ	 (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:

(i) Causing Cholera,

(ii) Fixing Nitrogen

(iii) Setting of curd

(iv) Baking of bread

(v) Causing Malaria

(vi) Causing Aids

Q4. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer: No, the microorganisms cannot be seen with the naked eyes. It can be seen only with the help of a microscope.

Q5. What are the major groups of microorganisms?

Answer: The major groups of microorganisms are :

A: Bacteria

B: Fungi

C: Protozoa

D: Some algae.

Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer: Some bacteria like Rhizobium and blue-green algae are able to fix nitrogen from the atmosphere and increase the fertility of the soil. These microbes are commonly called biological nitrogen fixers.

Q7. Write 10 lines on the usefulness of microorganisms in our lives.

Answer: Microbes are used for various purposes. They are very useful in our lives. Some of their uses are mentioned below:

1. The bacterium Lactobacillus promotes the formation of curd.
2. Bacteria are also involved in the making of cheese, pickles and many other food items.
3. Yeast is used for commercial production of alcohol and wine.
4. Yeast is also used for baking bread, cakes etc.
5. Microorganisms are used for the manufacturing of antibiotics
6. Vaccines for various diseases are made from microorganisms to protect the human beings and animals.
7. Some bacteria like Rhizobium and blue-green algae are able to fix nitrogen from the atmosphere and increase the fertility of the soil
8. Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.
9. The bacteria in our intestine help in digestion of food.
10. The algae are a food for some breeds of fish.

Q8. Write a short paragraph on the harms caused by microorganisms.

Answer: Although microorganisms are useful but there are some microorganisms which are harmful for us. Microorganisms cause diseases in human beings, plants and animals. Some microorganisms spoil food, clothing and leather. Some of the diseases caused by microorganisms are cholera, common cold, chicken pox and tuberculosis etc. There are some insects and animals which act as carriers of disease causing microbes. Some microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange etc. Microorganisms that grow on our food sometimes produce toxic substances which are poisonous and cause illness and even death.

Q9. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer: The medicines produced by microorganisms that kill or stop the growth of disease are called antibiotics. There are a number of antibiotics that are being produced by bacteria and fungi. The precautions which must be taken using antibiotics are:

• They should be taken on the advice of a qualified doctor.
• We must complete the course prescribed by the doctor.

Q10: Where can we find Microorganisms?

Answer: Microorganisms are found everywhere i.e. in the air, water, soil. They are found inside the bodies of plants and animals. They can live under different kinds of environment i.e. from very cold climate to hot springs and from deserts to marshy lands.


Q11: Name diseases caused by protozoa?

Answer: Malaria, Dysentery



Q12: Name the diseases caused by a virus.

Answer: common cold, flu, AIDS, polio, measles, hepatitis (jaundice)


Q13: Give examples of algae

Answer: Spirogyra, Chlamydomonas


Q14: Give names of fungi.

Answer: Rhizopus, Penicillium


Q15: Name any two protozoa.

Answer: Paramecium, Amoeba.


Q16: Name the organism and its type which converts milk into curd.

Answer: Lactobacillus - a type of bacteria.


Q17: Which microbe is used in the production of alcohol.

Answer: Yeast


Q18: Give an example of an antibiotic.

Answer: Streptomycin


Q19: Name the most common vector of communicable diseases.

Answer: housefly

Q20: Define the term fermentation.

Answer: The conversion of sugar solution into alcohol and liberation of carbon dioxide is known as fermentation. 

Q21: Why are children vaccinated?

Answer: When a disease causing microbe enters the human body, the body produces antibodies to fight the microbe. During vaccination, dead and weakened micro-organisms are introduced in a healthy body, the body produces antibodies, fights and kills them. Thus the body adapts to fight against that micro-organism and is immunized.

Q22: What is pasteurization?

Answer: Pasteurization is a technique applied to check the growth of micro-organisms in milk. The milk is heated to about 70 degrees and then suddenly chilled and stored.

Q23: What is the full form of AIDS?

Answer: Acquired Immuno Deficiency Syndrome

Q24: Define Immunity.

Answer: Immunity is the capacity of the body to defend itself against the disease.

Q25: List the type of bacteria recognised based on shape.

Answer: 

1. Rod shaped - Bacilli (a singular term is Bacillus)
2. Spherical Shaped - Cocci
3. Spiral Shaped - Spirillum
4. Comma Shaped - Vibrio

☛See also

Ch 2 - Micro-organisms - Friend and Foe (Q & A)
Ch2 - Micro-Organisms - Friend and Foe (MCQs)
Ch 2 - Micro-organisms  - Friends and Foes (Textbook Answers)
Ch 2 - Microorganisms - Friends and Foes (Q & A 2)

.