NCERT Solutions

1. Safe Drinking Water: Treatment of water to remove pathogens (e.g., prevention of Typhoid, Amoebiasis).
2. Proper Waste Disposal: Hygienic disposal of human excreta and garbage.
3. Vector Control: Cleaning stagnant water to prevent breeding of mosquitoes (Malaria, Dengue, Chikungunya). Use of mosquito nets and repellents.
4. Hygiene: Maintenance of personal and public hygiene (washing hands, clean food).
5. Vaccination: Immunization programs to prevent diseases like Polio, Diphtheria, Tetanus, etc.

• Identification of Pathogens: Biology helps identify the causative agents (bacteria, virus, fungi) of diseases.
• Understanding Life Cycles: Studying the life cycles of vectors (like mosquitoes) helps in devising control strategies (e.g., Gambusia fish for larvae).
• Vaccines: Understanding the immune system led to the development of vaccines (e.g., Smallpox eradication).
• Antibiotics: Discovery of antibiotics (like Penicillin) to kill bacteria.

• Use of clean, treated, or boiled water for drinking.
• Periodic cleaning and disinfection of water reservoirs and tanks.
• Proper disposal of sewage to prevent contamination of water bodies.
• Avoiding consumption of uncovered food or water from unhygienic sources.

In the context of DNA vaccines, a ‘suitable gene’ refers to a specific segment of DNA from the pathogen (virus or bacterium) that codes for an antigenic protein.

Mechanism: When this gene is introduced into the host body (via a vector like plasmid), the host cells express this gene to produce the pathogen’s protein (antigen). The immune system recognizes this protein as foreign and produces antibodies/memory cells against it, providing immunity without causing the actual disease.

• Primary Lymphoid Organs: Organs where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
  • Bone Marrow (B-cells and T-cells production).
  • Thymus (T-cells maturation).
• Secondary Lymphoid Organs: Organs where lymphocytes interact with antigens and proliferate.
  • Spleen, Lymph nodes, Tonsils, Peyer’s patches of small intestine, Appendix.

• (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.

• Y-shaped structure.
• Consists of 4 polypeptide chains: 2 Heavy (H) chains and 2 Light (L) chains (\(H_2L_2\)).
• Chains are held together by Disulphide bonds.
• Antigen Binding Site: Located at the tips of the ‘Y’ (Variable region).

1. Sexual Contact: With an infected person.
2. Blood Transfusion: Transfusion of contaminated blood and blood products.
3. Sharing Needles: Sharing infected needles (common in intravenous drug abusers).
4. Placental Transmission: From infected mother to child through placenta.

1. HIV enters the body and infects Macrophages (called HIV factory).
2. Viral RNA is converted to Viral DNA by Reverse Transcriptase enzyme.
3. Viral DNA incorporates into the host genome and directs the production of virus particles.
4. HIV enters Helper T-lymphocytes (TH cells), replicates, and destroys them.
5. This leads to a progressive decrease in the number of Helper T-cells.
6. Since TH cells are crucial for immunity, their reduction leaves the person susceptible to opportunistic infections (Mycobacterium, fungi), leading to immune deficiency.

Metastasis is the most feared property of malignant tumors. It is the process where cancerous cells detach from the primary tumor, travel through the blood or lymph system to distant parts of the body, and start a new tumor (secondary tumor) there.

• Immediate Effects: Reckless behavior, vandalism, violence. In high doses: Respiratory failure, heart failure, coma, death.
• Social Effects: Deteriorating relationships, financial loss, stealing, isolation, depression.
• Chronic Effects: Damage to nervous system and liver (Cirrhosis from alcohol).
• Use in Pregnancy: Adverse effect on the foetus.
• Intravenous Drug Use: High risk of AIDS and Hepatitis B.

Yes, peer pressure is a major factor.

1. Avoid Undue Peer Pressure: Have the confidence to say ‘No’ to things you are not comfortable with.
2. Education and Counseling: Accept failures as part of life; do not use drugs as an escape mechanism.
3. Seeking Help from Parents/Peers: Discuss problems immediately with trusted elders.
4. Looking for Danger Signs: Teachers and parents should be vigilant about behavioral changes.
5. Professional Help: Seek help from psychologists or de-addiction centers if needed.

It is difficult due to the psychological and physiological nature of Addiction and Dependence.

• Addiction: A psychological attachment to certain effects (euphoria) associated with drugs/alcohol.
• Tolerance: Repeated use increases the tolerance level of receptors, requiring higher doses for the same effect.
• Dependence: The body manifests unpleasant Withdrawal Syndrome (anxiety, shakiness, nausea, sweating) if the dose is stopped abruptly. To avoid this pain, the person continues usage, creating a vicious cycle.

1. Infection: Infected female Anopheles bites human, injecting Sporozoites.
2. Liver Stage: Sporozoites reach liver, reproduce asexually, bursting cells to release parasites.
3. RBC Stage: Parasites reproduce asexually in RBCs, bursting them to release Haemozoin (causes chill and fever).
4. Gametocytes: Sexual stages develop in RBCs.
5. Mosquito Stage: Mosquito takes up gametocytes. Fertilization occurs in mosquito gut. Sporozoites formed migrate to salivary glands.