Exercises
What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Answer
(i) Public hygiene: proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks; standard hygiene practices in public catering; supply of safe drinking water. (ii) Personal hygiene education: keeping the body clean and using clean water, food, vegetables and fruits. (iii) For air-borne diseases (pneumonia, common cold): avoiding close contact with infected persons and their belongings. (iv) Vector control for malaria, filariasis, dengue and chikungunya: avoiding stagnant water, cleaning household coolers, using mosquito nets and wire mesh on doors and windows, introducing larva-eating fish like Gambusia in ponds, spraying insecticides in ditches, drains and swamps. (v) Vaccination and immunisation programmes. (vi) Early diagnosis and proper treatment with antibiotics and other drugs, and health education campaigns.
In which way has the study of biology helped us to control infectious diseases?
Answer
(i) Identification of pathogens and their life cycles and modes of transmission (e.g. Plasmodium through female Anopheles) has allowed targeted measures such as vector control. (ii) Understanding of the immune system led to vaccines and immunisation programmes; smallpox has been eradicated, and polio, diphtheria, pneumonia and tetanus are largely controlled. (iii) Biotechnology (recombinant DNA technology) has made newer and safer vaccines, e.g. hepatitis B vaccine produced from yeast. (iv) Discovery of antibiotics and other drugs allows effective treatment. (v) Diagnostic tests such as ELISA help early detection, and knowledge of hygiene shapes public health measures.
How does the transmission of each of the following diseases take place? (a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia
Answer
(a) Amoebiasis (Entamoeba histolytica): through drinking water and food contaminated with faecal matter of infected persons; houseflies act as mechanical carriers, carrying the parasite from faeces to food.
(b) Malaria (Plasmodium): through the bite of an infected female Anopheles mosquito, which injects sporozoites into the blood; the mosquito becomes infected by biting an infected person.
(c) Ascariasis (Ascaris, roundworm): eggs passed in faeces of infected persons contaminate soil, water and plants; a healthy person is infected by taking contaminated water, vegetables, fruits, etc.
(d) Pneumonia (Streptococcus pneumoniae, Haemophilus influenzae): by inhaling droplets/aerosols released by an infected person, or by sharing glasses and utensils with an infected person.
What measure would you take to prevent water-borne diseases?
Answer
(i) Drink only safe water – boiled, filtered or chlorinated. (ii) Proper disposal of sewage and excreta, and avoiding open defecation, so that drinking water is not contaminated. (iii) Periodic cleaning and disinfection of water tanks, reservoirs and wells. (iv) Washing hands before eating and after using the toilet; washing fruits and vegetables properly. (v) Protecting food and water from houseflies, and maintaining hygiene in public eating places. (vi) Vaccination where available (e.g. typhoid).
Discuss with your teacher what does 'a suitable gene' means, in the context of DNA vaccines.
Answer
A DNA vaccine contains a gene (in a plasmid or other vector) that, when introduced into the body, makes our own cells produce a protein of the pathogen. A suitable gene is one that codes for an antigenic protein of the pathogen (for example a surface or coat protein) which can trigger a strong, specific immune response (antibodies and memory cells), but which by itself cannot cause the disease. It should be stable, expressible in human cells, and represent a part of the pathogen that does not change much, so that the immunity is protective. For hepatitis B, for example, the gene for the surface antigen (HBsAg) is used.
Name the primary and secondary lymphoid organs.
Answer
Primary lymphoid organs: bone marrow and thymus (where immature lymphocytes differentiate into antigen-sensitive lymphocytes). Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix (also MALT), where lymphocytes interact with antigens and proliferate into effector cells.
The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT (b) CMI (c) AIDS (d) NACO (e) HIV
Answer
(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
Differentiate the following and give examples of each: (a) Innate and acquired immunity (b) Active and passive immunity
Answer
(a) Innate immunity is non-specific defence present from birth; it acts through barriers. Examples: physical barriers (skin, mucus coating of respiratory, gastrointestinal and urogenital tracts), physiological barriers (acid in stomach, saliva, tears), cellular barriers (neutrophils, monocytes, natural killer lymphocytes, macrophages) and cytokine barriers (interferons from virus-infected cells). Acquired immunity is pathogen-specific, develops during life after exposure to an antigen and has memory; it shows a weak primary response and a rapid, intense secondary (anamnestic) response, through B-lymphocytes (antibodies, humoral) and T-lymphocytes (cell-mediated). Example: lifelong immunity after chickenpox; graft rejection by T-cells.
(b) Active immunity is produced when the body's own immune system makes antibodies after exposure to antigens (live or dead microbes or proteins); it is slow to develop but long-lasting. Examples: natural infection, vaccination (e.g. polio vaccine). Passive immunity is given by ready-made antibodies from outside; it acts quickly but is short-lived. Examples: IgG from mother to foetus through placenta, IgA in colostrum, and injection of preformed antibodies or antitoxins (e.g. anti-tetanus serum, snake antivenom).
Draw a well-labelled diagram of an antibody molecule.
Answer
The antibody is a Y-shaped molecule made of four peptide chains, written H₂L₂: two long heavy chains and two short light chains, held together by disulphide bonds. Labels: the two arms each with an antigen-binding site at the tip (formed by the variable regions of one heavy and one light chain); constant regions of the heavy and light chains; the hinge region where the arms join; and the stem formed by the two heavy chains. Types include IgA, IgM, IgE and IgG.
What are the various routes by which transmission of human immuno-deficiency virus takes place?
Answer
(a) Sexual contact with an infected person; (b) transfusion of contaminated blood and blood products; (c) sharing infected needles and syringes, as among intravenous drug abusers; (d) from an infected mother to her child through the placenta. HIV is not spread by mere touch or physical contact; it spreads only through body fluids.
What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Answer
HIV is a retrovirus with an RNA genome. After entering the body it infects macrophages, where its RNA is copied into viral DNA by reverse transcriptase. This viral DNA is incorporated into the host cell's DNA and directs the cell to produce new virus particles, so macrophages act as an HIV factory. At the same time HIV enters helper T-lymphocytes (TH), multiplies, and the progeny viruses released into blood attack more helper T-cells. This cycle repeats, steadily reducing the number of helper T-lymphocytes. Since helper T-cells are needed for both antibody and cell-mediated responses, the person becomes immuno-deficient and suffers from fever, diarrhoea, weight loss and infections that would otherwise be overcome (e.g. Mycobacterium, viruses, fungi, Toxoplasma).
How is a cancerous cell different from a normal cell?
Answer
(i) Normal cells divide in a controlled, regulated way; in cancer cells these regulatory mechanisms break down and cells divide uncontrollably. (ii) Normal cells show contact inhibition – contact with neighbouring cells stops their growth; cancer cells lose contact inhibition and form masses called tumours. (iii) Normal cells stay in place and differentiate; malignant cancer cells grow rapidly, invade and damage neighbouring tissue, starve normal cells by competing for nutrients, and can spread to distant parts (metastasis). (iv) Cancer cells arise by oncogenic transformation, often through activation of cellular oncogenes (proto-oncogenes) by carcinogens.
Explain what is meant by metastasis.
Answer
Metastasis is the property of malignant tumours by which cells sloughed off from the tumour travel through the blood (or lymph) to distant sites in the body and, wherever they get lodged, start forming new tumours. It is the most feared property of malignant tumours.
List the harmful effects caused by alcohol/drug abuse.
Answer
(i) Immediate effects: reckless behaviour, vandalism and violence. (ii) Excessive doses can cause coma and death due to respiratory failure, heart failure or cerebral haemorrhage; mixing drugs or taking them with alcohol often causes overdose and death. (iii) Warning signs: falling academic performance, unexplained absence, poor personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, damaged relationships, changes in sleep, eating and weight. (iv) Intravenous drug users risk AIDS and hepatitis B from shared needles. (v) Chronic use damages the nervous system and liver (cirrhosis); use during pregnancy harms the foetus. (vi) Alcohol in adolescence can lead to heavy drinking in adulthood. (vii) Social effects: stealing to buy drugs, mental and financial distress to family and friends. (viii) Misuse of anabolic steroids by sportspersons causes masculinisation, mood swings and abnormal cycles in females, and reduced testes, decreased sperm production, liver and kidney problems and premature baldness in males.
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
Yes. Peer pressure is a major factor in adolescents starting to smoke, drink or take drugs, often by presenting it as "cool" or adventurous. To protect oneself: (i) learn to say a firm "no" and not give in to undue peer pressure; (ii) choose friends who do not use drugs or alcohol; (iii) seek help and guidance from parents, teachers, trusted friends or counsellors; (iv) learn correct facts about the harmful and addictive effects of drugs and alcohol; (v) spend time and energy on healthy pursuits like sports, reading, music, yoga and other activities; (vi) learn to handle stress and accept failures as part of life.
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
(i) Addiction: drugs and alcohol give euphoria and a temporary feeling of well-being, creating a psychological attachment that drives repeated use even when it becomes self-destructive. (ii) Tolerance: with repeated use, the tolerance level of the body's receptors rises, so they respond only to higher doses, leading to greater intake. (iii) Dependence: if the regular dose is stopped suddenly, the body shows an unpleasant withdrawal syndrome – anxiety, shakiness, nausea and sweating – which is relieved only when use is resumed; withdrawal can even be life-threatening. These together trap the user in a vicious circle, so quitting usually needs medical help and counselling.
In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
Answer
Motivating factors: curiosity and experimentation; need for adventure and excitement; using them to escape problems; stress from pressure to excel in studies and examinations; the perception that smoking, drinking or drugs are "cool" or progressive, promoted by TV, movies, newspapers and the internet; unstable or unsupportive families; and peer pressure.
Avoidance: (i) avoid undue peer pressure and do not push children beyond their limits; (ii) education and counselling to face problems, stress, disappointments and failures; channel energy into sports, reading, music, yoga and hobbies; (iii) seek help from parents, peers and trusted friends; (iv) parents and teachers should look for danger signs and act early; (v) seek professional and medical help from psychologists, psychiatrists, and de-addiction and rehabilitation programmes when needed. Parenting with high nurturance and consistent discipline lowers the risk.
Important Extra Questions
Which substance released from ruptured RBCs causes the recurring chill and fever in malaria?
Answer
Haemozoin, a toxic substance released when Plasmodium ruptures RBCs; fever recurs every three to four days.
What is an allergy? Name the antibody and chemicals involved.
Answer
An exaggerated immune response to certain environmental antigens (allergens) such as dust mites, pollen and animal dander. IgE antibodies are produced, and mast cells release chemicals like histamine and serotonin. Antihistamines, adrenaline and steroids reduce the symptoms.
What is autoimmunity? Give an example.
Answer
A condition in which the immune system attacks the body's own cells, due to genetic or unknown reasons; e.g. rheumatoid arthritis.
Name the source plant and effect of cocaine.
Answer
Obtained from the coca plant Erythroxylum coca; it interferes with transport of the neurotransmitter dopamine, stimulates the central nervous system and gives euphoria and increased energy; excess causes hallucinations.
Name the test used to diagnose AIDS. Can anti-retroviral drugs cure it?
Answer
ELISA (enzyme linked immuno-sorbent assay). No; anti-retroviral drugs are only partially effective and can only prolong the patient's life.