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NCERT Solutions · Class 12 Biology Human Health and Disease

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Exercises 7.1–7.10 (part 1 of 2)

  1. Exercise 7.1

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

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    The safeguards are hygiene, safe food and water, proper waste disposal, vector control and immunisation.
    Personal hygiene — keep the body clean; consume only clean drinking water, food, vegetables and fruits.
    Public hygiene — proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks; observing standard practices of hygiene in public catering.
    These are particularly essential where the agent travels through food and water — typhoid, amoebiasis and ascariasis.
    For air-borne diseases such as pneumonia and the common cold, add one more measure: avoid close contact with infected persons or their belongings.
    For vector-borne diseases such as malaria, filariasis, dengue and chikungunya, the most important measure is to control or eliminate the vectors and their breeding places — avoid stagnation of water in and around residential areas, clean household coolers regularly, use mosquito nets, introduce larvivorous fishes like Gambusia in ponds, spray insecticides in ditches, drainage areas and swamps, and fit doors and windows with wire mesh.
    Vaccination (immunisation) against infectious diseases, on a programme scale.
    Awareness and education about diseases and their effect on bodily functions — as NACO and NGOs do for AIDS.

  2. Exercise 7.2

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

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    Biology armed us with vaccines, antibiotics and diagnostic tests, and with the knowledge of how pathogens live and spread.
    Vaccines and immunisation programmes have completely eradicated a deadly disease like smallpox; polio, diphtheria, pneumonia and tetanus have been controlled to a large extent.
    Biotechnology is on the verge of making newer and safer vaccines — recombinant DNA technology lets antigenic polypeptides of a pathogen be produced in bacteria or yeast, allowing large-scale production and greater availability, e.g. hepatitis B vaccine produced from yeast.
    Discovery of antibiotics and various other drugs has enabled us to treat infectious diseases effectively.
    Diagnosis improved: typhoid is confirmed by the Widal test, AIDS by ELISA — early detection allows early treatment and stops onward spread.
    Working out pathogen life cycles showed us where to break transmission — knowing that Plasmodium needs the female Anopheles as a vector makes vector control a cure-free way of stopping malaria.

  3. Exercise 7.3

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

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    (a) Amoebiasis
    Through drinking water and food contaminated by faecal matter — this is the main source of infection with Entamoeba histolytica.
    Houseflies act as mechanical carriers, transmitting the parasite from the faeces of an infected person to food and food products, thereby contaminating them.
    (b) Malaria
    Through the bite of an infected female Anopheles mosquito, which is the vector.
    Plasmodium enters the human body as sporozoites — the infectious form stored in the mosquito's salivary glands.
    The mosquito itself picks up the parasite when it bites an infected person, so the cycle needs two hosts, human and mosquito.
    (c) Ascariasis
    Through contaminated water, vegetables, fruits, etc.
    The eggs of Ascaris are excreted along with the faeces of infected persons and contaminate soil, water and plants; a healthy person then takes them in.
    (d) Pneumonia
    By inhaling the droplets/aerosols released by an infected person.
    Also by sharing glasses and utensils with an infected person.

  4. Exercise 7.4

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

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    The measures are those of personal and public hygiene, aimed at keeping faecal matter out of what we drink and eat.
    Consume only clean drinking water — water-borne diseases such as typhoid, amoebiasis and ascariasis spread through contaminated water.
    Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.
    Proper disposal of waste and excreta, so that faecal matter never reaches the water supply.
    Observe standard practices of hygiene in public catering, and use clean food, vegetables and fruits.
    Keep houseflies away from food, since they act as mechanical carriers from faeces to food.
    Keep the body clean — the chapter treats personal hygiene as inseparable from public hygiene here.

  5. Exercise 7.5

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

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    The chapter does not cover DNA vaccines, and the exercise itself asks you to discuss this with your teacher.
    What the chapter does give is the principle of vaccination: a preparation of the antigenic proteins of the pathogen, or an inactivated/weakened pathogen, is introduced into the body; the antibodies raised against these antigens then neutralise the real pathogen during actual infection, and memory B- and T-cells recognise it quickly on later exposure.
    It also gives the recombinant DNA route: antigenic polypeptides of a pathogen can be produced in bacteria or yeast, e.g. hepatitis B vaccine produced from yeast.
    Read together, these two ideas point to what 'a suitable gene' would have to be — the gene coding for an antigenic protein of the pathogen, one that provokes an immune response and memory without being able to cause the disease. Note clearly that this last step is an inference; the chapter does not state it.

  6. Exercise 7.6

    Name the primary and secondary lymphoid organs.

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    Primary lymphoid organs — bone marrow and thymus.
    Secondary lymphoid organs — spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix.
    The primary organs are where immature lymphocytes differentiate into antigen-sensitive lymphocytes; both bone marrow and thymus provide the micro-environments for the development and maturation of T-lymphocytes, and the bone marrow is the main lymphoid organ where all blood cells, including lymphocytes, are produced.
    After maturation the lymphocytes migrate to the secondary lymphoid organs, which provide the sites for interaction of lymphocytes with the antigen, after which they proliferate to become effector cells.
    Lymphoid tissue also lies within the lining of the major tracts — respiratory, digestive and urogenital — and is called MALT (mucosa-associated lymphoid tissue); it constitutes about $\displaystyle 50$ per cent of the lymphoid tissue in the human body. The chapter describes MALT as lymphoid tissue and does not place it in either the primary or the secondary class, so do not label it as one in the answer.

  7. Exercise 7.7

    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

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    (a) MALT — Mucosa-Associated Lymphoid Tissue
    (b) CMI — Cell-Mediated Immunity (cell-mediated immune response)
    (c) AIDS — Acquired Immuno Deficiency Syndrome
    (d) NACO — National AIDS Control Organisation
    (e) HIV — Human Immuno deficiency Virus

  8. Exercise 7.8

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

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    (a) Innate and acquired immunity
    Innate immunity is non-specific and is present at the time of birth; acquired immunity is pathogen-specific and is characterised by memory.
    Innate immunity works by putting up barriers to entry; acquired immunity acts after the pathogen is met, and remembers it.
    Acquired immunity gives a low-intensity primary response on the first encounter and a highly intensified secondary (anamnestic) response on a later encounter with the same pathogen. Innate immunity shows no such change.
    Innate immunity is carried out by four barriers; acquired immunity is carried out by B-lymphocytes and T-lymphocytes.
    Examples of innate immunity — physical: skin, and the mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts; physiological: acid in the stomach, saliva in the mouth, tears from the eyes; cellular: PMNL-neutrophils, monocytes, natural killer lymphocytes and tissue macrophages that phagocytose microbes; cytokine: interferons secreted by virus-infected cells.
    Examples of acquired immunity — antibodies (IgA, IgM, IgE, IgG) in the blood, i.e. the humoral immune response; and cell-mediated immunity, by which the body distinguishes 'self' from 'nonself' and rejects a graft.
    (b) Active and passive immunity
    Active immunity is produced when the host is exposed to antigens — living or dead microbes or other proteins — and makes its own antibodies. Passive immunity is when ready-made antibodies are directly given to the body.
    Active immunity is slow and takes time to give its full effective response; passive immunity acts at once, which is why it is used where a quick response is needed, as in tetanus.
    Examples of active immunity — antibodies raised during a natural infection, and those raised by deliberate injection of microbes during immunisation (vaccination).
    Examples of passive immunity — the yellowish colostrum secreted by the mother in the initial days of lactation, rich in IgA antibodies for the infant; antibodies the foetus receives from the mother through the placenta during pregnancy; the preformed antitoxin injected in tetanus; and the preformed antibodies against snake venom given after a snakebite.

  9. Exercise 7.9

    Draw a well-labelled diagram of an antibody molecule.

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    ncert_XII_Biology_fig_7-9
    What the diagram must show: an antibody is H\(\displaystyle _2\)L\(\displaystyle _2\) — four peptide chains, two small ones called light chains and two longer ones called heavy chains.
    Draw the molecule as a Y, which is the shape the chapter's Figure $\displaystyle 7.4$ uses.
    The two heavy chains are the long chains: draw each one running from the tip of one arm of the Y, down through the fork, into the stem. Together they make the whole stem and the inner half of both arms. Shade or hatch them differently from the light chains.
    The two light chains are the short chains: draw one lying alongside the outer part of each arm, from the tip of the arm down to the fork. They do not reach the stem.
    The molecule is symmetrical — the left arm and the right arm must be drawn identically.
    Labels to write, with lead lines: Light chain (L) on each of the two short chains; Heavy chain (H) on each of the two long chains; antigen-binding site at the tip of each of the two arms. Write H\(\displaystyle _2\)L\(\displaystyle _2\) beside the figure and title it Structure of an antibody molecule.
    Give the figure a caption naming it an antibody; the chapter calls its own picture a cartoon, so a clean two-tone outline is enough — nothing finer is required.
    Note for accuracy: the chapter's running text names only the four chains and the formula H\(\displaystyle _2\)L\(\displaystyle _2\); the Y outline is what its Figure $\displaystyle 7.4$ draws.

  10. Exercise 7.10

    What are the various routes by which transmission of human immuno- deficiency virus takes place?

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    HIV is transmitted by four routes:
    (a) Sexual contact with an infected person.
    (b) Transfusion of contaminated blood and blood products.
    (c) Sharing infected needles, as in the case of intravenous drug abusers.
    (d) From an infected mother to her child through the placenta.
    High-risk groups therefore are individuals with multiple sexual partners, drug addicts who take drugs intravenously, individuals who require repeated blood transfusions, and children born to an HIV-infected mother.
    It is important to note that HIV/AIDS is not spread by mere touch or physical contact — it spreads only through body fluids. Infected persons must therefore not be isolated from family and society.