Chapter 8: Human Health and Disease Class 12 Biology NCERT Solutions

NCERT Solutions for Class 12 Biology Chapter 8 – Human Health and Disease

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

The various public health measures against infectious diseases include the following:

• Education: People should be educated about infectious diseases so they can protect themselves.
• Isolation: Infected individuals should be isolated to prevent transmission.
• Vaccination: Vaccines should be taken to prevent infections like cholera, typhoid, and TB.
• Sanitation: Public hygiene involves proper disposal of waste, clean water, and personal hygiene practices.
• Eradication of vectors: Destroy vector breeding grounds and kill adult vectors using appropriate methods.

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

The study of biology, particularly pathology, helps identify pathogens, understand host responses, diagnose diseases, and develop preventive and curative measures like vaccines and antibiotics. This understanding has greatly aided in controlling infectious diseases.

3. How does the transmission of each of the following diseases take place?
(a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia

• (a) Amoebiasis: Transmitted through contaminated food or water containing amoebic cysts.
• (b) Malaria: Spread by female Anopheles mosquito, which transmits the parasite during its bite.
• (c) Ascariasis: Spread through contaminated vegetables, fruits, or water with parasite eggs.
• (d) Pneumonia: Spread via cough, sneezing, and sharing utensils with infected individuals.

4. What measures would you take to prevent water borne diseases?

Water borne diseases can be prevented through:

• Oral rehydration therapy
• Health education
• Controlling reservoirs
• Immunization
• Ensuring general hygiene and consumption of pure water

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

In DNA vaccines, ‘a suitable gene’ refers to a gene that encodes an antigenic protein. This gene is inserted into a plasmid, which, when introduced into the host, expresses the protein and triggers an immune response, preparing the body to fight the actual pathogen.

6. Name the primary and secondary lymphoid organs.

• Primary lymphoid organs: Bone marrow and thymus
• Secondary lymphoid organs: Spleen, lymph nodes, tonsils

7. Expand the following abbreviations:

• (a) MALT: Mucosa Associated Lymphoid Tissue
• (b) CMI: Cell-Mediated Immunity
• (c) AIDS: Acquired Immuno Deficiency Syndrome
• (d) NACO: National AIDS Control Organisation
• (e) HIV: Human Immunodeficiency Virus

8. Differentiate the following and give examples of each:
(a) Innate and acquired immunity
(b) Active and passive immunity

(a) Innate vs Acquired Immunity:

• Innate immunity is present from birth and is non-specific, e.g., skin, lysozyme in tears.
• Acquired immunity is developed through exposure to pathogens or via vaccination, and it is specific, e.g., antibodies formed after infection.

(b) Active vs Passive Immunity:

• Active immunity is developed when the body produces its own antibodies (e.g., through vaccination).
• Passive immunity involves direct transfer of antibodies (e.g., maternal antibodies through placenta).

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

(Refer to NCERT textbook for the labelled diagram of an antibody.)

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

• Unprotected sexual contact with infected individuals
• Sharing needles among intravenous drug users
• Transfusion of contaminated blood
• From infected mother to child during pregnancy or breastfeeding

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

HIV infects helper T-cells and uses reverse transcriptase to integrate its genetic material into host DNA. It replicates rapidly, mutates frequently, and destroys T-cells, weakening the immune system. This makes the body vulnerable to opportunistic infections and certain cancers, eventually leading to death if untreated.

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

Cancerous cells divide uncontrollably, lose the ability to undergo apoptosis (programmed cell death), and can spread to other parts of the body (metastasis). In contrast, normal cells divide in a regulated manner and stay within their original tissue boundaries.

13. Explain what is meant by metastasis.

Metastasis is the spread of cancer cells from the original (primary) site to distant organs, forming secondary tumors. This occurs via blood or lymphatic system and is a hallmark of malignant tumors.

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

Alcohol abuse effects:

• Heart issues due to blood vessel damage
• Gastritis and ulcers
• Nerve inflammation (neuritis)
• Liver damage (cirrhosis)

Drug abuse effects:

• Coma and death from overdose
• Behavioral changes: depression, aggression
• Infections like AIDS and hepatitis from needle sharing
• Violent and reckless behavior

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?

Yes, peer pressure can lead one to experiment with drugs or alcohol. One can avoid this influence by:

• Resisting peer pressure
• Seeking counseling when needed
• Talking to trusted adults or parents
• Staying away from negative influences

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

Addiction creates both psychological and physical dependence. With repeated use, tolerance builds, requiring higher doses to feel the same effect. This creates a cycle of dependence, making it hard to quit without support or rehabilitation.

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

Youth may turn to drugs or alcohol due to stress, peer pressure, curiosity, or lack of guidance. Prevention strategies include:

• Open communication with children
• Monitoring their activities and friends
• Setting a good example
• Keeping harmful substances out of reach
• Educating them about drug abuse and its consequences