NCERT Class 12 Biology: Chapter – 8 Human Health and Diseases Part 6

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Question 4:

“Prevention is better than cure” . Comment.


“Prevention is better than cure” the saying is true. It is because if any disease enters the body it may cause irreparable damage and discomfort to the affected person. Hence, prevention is a better option.

Question 5:

Explain any three preventive measures to control microbial infections.


Three preventive measures to control microbial infections are:

1. Overcrowded places should be avoided. So as to avoid exposure to already infected people and other microbes in the air.

2. Preventive vaccination could be done.

3. Personal as well as community hygiene should be maintained so as to avoid the growth of microbes.

Question 6:

In the given flow diagram, the replication of retrovirus in a host is shown. Observe and answer the following questions.

a. Fill in (1) and (2)

b. Why is the virus called retrovirus?

c. Can the infected cell survive while viruses are being replicated and released?

Chapter-8- Question -6- Flow Chart

Answer: 1. A. Block 1: Viral DNA is produced by reverse transcriptase.

B. Block 2: New viral RNA is produced by the infected cell.

2. RNA is the genetic material of this virus. So it produces DNA by reverse transcription. Hence, it does not follow central dogma hence , is known as retrovirus.

3. Yes, the infected cell survives while viruses are being replicated and released.

Question 7:

“Maintenance of personal and public hygiene is necessary for prevention and control of many infectious diseases” . Justify the statement giving suitable examples.


Maintenance of personal and public hygiene is necessary for prevention and control of many infectious diseases because if the hygiene is not maintained microbes would grow and would easily get transmitted.

It can be maintained by taking the following measures:

1. Education: People should be well informed about hygiene, communicable disease and their prevention.

2. Sanitation: Proper sanitation should be provided so that air and water would not get contaminated.

3. Isolation: Infected person should be kept isolated from the rest to minimise the spread of infection.

4. Vaccination: Proper vaccination should be done to control the spread of infection.

5. Sterilisation: It should be done to avoid spreading of infection.