Chapter 7: Human Health and Disease (Biology and Human Welfare)

• Personal hygiene: keeping the body clean, drinking clean water, eating clean food.
• Public hygiene: proper disposal of waste and excreta, periodic cleaning of water tanks, pools and drains, standard practices in public catering.
• Control of vectors: removing stagnant water and breeding sites of mosquitoes, spraying insecticides, using nets and repellents, introducing fish like Gambusia that eat mosquito larvae.
• Isolation and treatment of infected persons; avoiding contact with their articles.
• Vaccination and immunisation programmes.
• Health education and awareness.

Personal and public hygiene, clean water and food, vector control, isolation of patients, vaccination and awareness.

• It identified the causes (pathogens) of diseases and how they spread (e.g. the mosquito in malaria), so preventive measures could be taken.
• It led to vaccines and immunisation programmes (e.g. smallpox has been eradicated; polio nearly so).
• It gave us antibiotics and other drugs to treat infections.
• It helped vector control and better hygiene and sanitation.

By finding pathogens and their modes of spread, and developing vaccines, antibiotics, drugs and vector control.

• (a) Amoebiasis (Entamoeba histolytica): through food and water contaminated with faeces containing cysts; houseflies act as mechanical carriers.
• (b) Malaria (Plasmodium): by the bite of an infected female Anopheles mosquito.
• (c) Ascariasis (Ascaris): eggs passed in the faeces of an infected person contaminate soil, water and vegetables; a healthy person is infected by eating contaminated food or drinking contaminated water.
• (d) Pneumonia (Streptococcus pneumoniae, Haemophilus influenzae): by inhaling droplets or aerosols released by an infected person, or by sharing their glasses and utensils.

(a) Faecal contamination of food/water (cysts); (b) bite of female Anopheles; (c) eggs in contaminated food, water, soil; (d) droplets from infected persons.

• Drink boiled, filtered or chlorinated water.
• Keep water tanks and containers clean and covered; clean them periodically.
• Dispose of sewage and excreta properly so they do not mix with drinking water.
• Wash hands with soap before eating and after using the toilet.
• Avoid eating uncovered or unhygienic food.

Boiled/chlorinated water, clean covered storage, proper sewage disposal and hand washing.

In a DNA vaccine, a suitable gene is a gene from the pathogen that codes for an antigenic protein (one that can trigger an immune response but cannot cause the disease itself). This gene is put into the body (in a plasmid); body cells make the antigen, and the immune system produces antibodies and memory cells against the pathogen.

A pathogen gene that codes for a harmless antigen able to trigger immunity.

• Primary lymphoid organs (where lymphocytes form and mature): bone marrow and thymus.
• Secondary lymphoid organs (where lymphocytes meet antigens): spleen, lymph nodes, tonsils, Peyer's patches of the small intestine, appendix and MALT.

Primary: bone marrow and thymus. Secondary: spleen, lymph nodes, tonsils, Peyer's patches, appendix and MALT.

• (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

As expanded above.

(a)

(b)

(a) Innate: inborn, non-specific (skin); acquired: specific with memory (after infection). (b) Active: body makes antibodies (vaccine); passive: ready-made antibodies (colostrum, antitoxin).

An antibody is a Y-shaped molecule made of four polypeptide chains: two heavy (H) chains and two light (L) chains (H₂L₂), joined by disulphide bonds.

Labels to show: antigen-binding sites (at the tips of the two arms), variable region and constant region of each chain, heavy chain, light chain, disulphide (S–S) bonds, hinge region.

A Y-shaped H₂L₂ molecule; label the antigen-binding sites, variable and constant regions, heavy and light chains and disulphide bonds.

• Sexual contact with an infected person.
• Transfusion of contaminated blood or blood products.
• Sharing infected needles (as among intravenous drug users).
• From an infected mother to her child through the placenta (and during birth or breastfeeding).

Unsafe sex, infected blood transfusion, shared needles, and from mother to child.

• HIV enters the body and infects macrophages, which act as an "HIV factory": the viral RNA is copied into DNA by reverse transcriptase, which is inserted into the host DNA and directs production of new viruses.
• The virus then enters helper T-lymphocytes (T_H cells), replicates and destroys them.
• The number of helper T cells steadily falls. Since these cells are needed to activate both B cells and other T cells, the immune system becomes very weak.
• The person then suffers from infections (opportunistic infections such as Mycobacterium, viruses, fungi and Toxoplasma) that a healthy body could fight.

HIV multiplies in macrophages and destroys helper T cells, so the immune response collapses and opportunistic infections follow.

• Normal cells show contact inhibition: they stop dividing when they touch other cells. Cancer cells have lost contact inhibition and divide uncontrollably, forming masses called tumours.
• Cancer cells are often abnormal in shape and do not differentiate properly.
• Malignant cancer cells can invade nearby tissues and spread to other parts (metastasis).

Cancer cells lose contact inhibition and divide uncontrollably, forming tumours, and can invade and spread.

Metastasis is the spread of cancer cells from a malignant tumour to distant parts of the body through the blood or lymph. The cells reach new sites and start new tumours there. It is the most feared property of malignant tumours.

The spread of cancer cells from a malignant tumour to distant sites through blood or lymph, forming new tumours.

• Immediate: reckless behaviour, vandalism and violence; overdose can cause coma and death (respiratory failure, heart failure, cerebral haemorrhage).
• Behavioural signs: fall in academic performance, absence from school, loss of interest, isolation, depression, fatigue, aggressive behaviour, deteriorating relationships.
• Health damage: liver cirrhosis and nervous system damage (alcohol); infections like AIDS and hepatitis B from shared needles; drug use in pregnancy harms the foetus.
• Social and financial problems: stealing to buy drugs, family distress.
• Misuse of anabolic steroids causes side effects such as aggression, mood swings, acne and, in females, masculinisation; in males, breast enlargement and reduced sperm production.

Violent and reckless behaviour, poor studies, depression, organ damage (liver, nerves), infections like AIDS and hepatitis, family and financial problems, and even death.

Yes. Peer pressure is a major reason young people start taking alcohol or drugs. To protect oneself:

• Say no firmly and avoid friends who pressure you.
• Choose friends with healthy habits; take part in sports, reading, music and other hobbies.
• Talk to parents, teachers or counsellors about any pressure or problem.
• Learn the facts about the harmful effects of drugs and alcohol.
• Seek professional help early if tempted.

Yes; refuse firmly, avoid such company, keep healthy hobbies, and seek help from parents, teachers or counsellors.

Drugs and alcohol cause addiction: a psychological attachment to the "high" they give, so the person feels driven to use them again. With repeated use, the body develops tolerance (more is needed for the same effect) and dependence. If use stops suddenly, withdrawal symptoms appear (anxiety, shakiness, nausea, sweating), which can be severe. To avoid these, the person keeps using the substance, so the habit is very hard to break.

They cause addiction, tolerance and dependence, and stopping brings painful withdrawal symptoms.

Reasons: curiosity, peer pressure, a wish for adventure or excitement, wanting to look grown-up, escaping stress, frustration or depression (exams, family problems), and the influence of family members or media.

Prevention:

• Avoid undue pressure on children to perform; parents and teachers should guide them supportively.
• Education and counselling about the dangers.
• Encourage healthy activities: sports, reading, music, yoga.
• Seek help from parents, peers and professionals; look for early warning signs.

Curiosity, peer pressure, stress and escape; prevented by support without undue pressure, education and counselling, healthy activities, and early help.