Class 12 Biology

Health and Disease

NCERT Exercise

Question 1. What are the various public health measures, which you would suggest as safeguard against infectious diseases?

Answer: Following public health measures can provide safeguard against infectious diseases:

Question 2. In which way has the study of biology helped us to control infectious diseases?

Answer: Study of biology has helped us in controlling infectious diseases in following ways:

Question 3. How does the transmission of each of the following diseases take place?

(a) Amoebiasis

Answer: Through contaminated food and water

(b) Malaria

Answer: Through bite of female Anopheles mosquito

(c) Ascariasis

Answer: Through contaminated vegetables and fruits

(d) Pneumonia

Answer: Through droplets in air

Question 4. What measure would you take to prevent water-borne diseases?

Answer: Water borne diseases can be prevented by taking following steps:

Question 5. Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.

Answer: DNA vaccine involves injecting genetically engineered DNA of the causative pathogen. This helps the body in directly producing antibodies against the pathogen.

Question 6. Name the primary and secondary lymphoid organs.

Answer: Primary Lymphoid Organs: Bone marrow and thymus

Secondary Lymphoid Organs: spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix

Question 7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:

(a) MALT

Answer: Mucosal Associated Lymphoid Tissue

(b) CMI

Answer: Cell Mediated Immunity

(c) AIDS

Answer: Acquired Immuno Deficiency Syndrome

(d) NACO

Answer: National Aids Control Organisation

(e) HIV

Answer: Human Immuno Deficiency Virus

Question 8. Differentiate the following and give examples of each:

(a) Innate and acquired immunity

Answer: Innate immunity is present at the time of birth, but acquired immunity develops during one’s lifetime. Innate immunity is non-specific in nature, while active immunity is specific to a particular pathogen.

(b) Active and passive immunity

Answer: When the host cell produces antibodies in response to an antigen, it is called active immunity, When readymade antibodies are injected into the body, it gives passive immunity.

Question 9. Draw a well-labelled diagram of an antibody molecule.


figure of antibody molecule

Question 10. What are the various routes by which transmission of human imunodeficiency virus takes place?

Answer: Following are the routes for transmission of HIV:

Question 11. What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?

Answer: HIV enters into helper T-lymphocytes (TH), replicates and produce progeny viruses. The progeny viruses are released in the blood and begin to attack other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T-lymphocytes in the body. This weakens the immune system of the patient.

Question 12. How is a cancerous cell different from a normal cell?

Answer: Normal cells stop dividing after certain rounds of cell division. But cancer cells continue to divide endlessly.

Question 13. Explain what is meant by metastasis.

Answer: Cancer cells from a tumor reach other parts of the body through blood. These cells begin to form tumors in other parts of the body. This phenomenon is called metastasis.

Question 14. List the harmful effects caused by alcohol/drug abuse.

Answer: Following are the harms of alcohol/drug abuse:

Question 15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?

Answer: Peer pressure can have a profound effect on a person. Sometimes, friends may influence a person to take alcohol/drugs; in order to show conformity with group behavior. One needs to be alert to such signals. In case of even a minor signal, one needs to cut off from such a group. A person also needs to confide such instances with his/her parents because parents are probably the best guides to help in rescue.

Question 16. Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.

Answer: Drugs are frequently used because of their perceived benefits. The inherent addictive nature of these substances results in addiction and dependence. Addiction is a psychological attachment to various effects of a substance. So, a person continues to take addictive substance even when he does not need it in the real sense. Tolerance level of the receptors ion our body increases with repeated use of addictive substances. This results in body craving for higher doses. Thus, it becomes difficult to get rid of the habit.

Question 17. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?

Answer: Conformity to group behavior, need for experimentation and excitement, curiosity, etc. can motivate a person to take to alcohol or drugs. This can be avoided by following various steps. One should make friends with his/her parents. One should develop a disciplined lifestyle; in terms of daily routine. One should inculcate some artistic hobbies; like painting, music, photography, etc.