SolveItClass 12 · NCERT

NCERT Solutions · Class 12 Biology Human Health and Disease

17 questions · 17 still being checked

Exercises 7.11–7.17 (part 2 of 2)

  1. Exercise 7.11

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

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    The virus destroys the helper T-lymphocytes (T\(\displaystyle _H\)), and their progressive fall leaves the person unable to fight infections.
    After getting into the body, the virus enters macrophages, where the RNA genome replicates to form viral DNA with the help of the enzyme reverse transcriptase.
    This viral DNA gets incorporated into the host cell's DNA and directs the infected cells to produce virus particles. The macrophage keeps producing virus and thus acts like an HIV factory.
    Simultaneously, HIV enters helper T-lymphocytes, replicates in them and produces progeny viruses.
    The progeny viruses released into the blood attack other helper T-lymphocytes, and this is repeated, leading to a progressive decrease in the number of helper T-lymphocytes.
    During this period the person suffers from bouts of fever, diarrhoea and weight loss.
    With too few helper T-lymphocytes left, the person starts suffering from infections that could otherwise have been overcome — bacteria, especially Mycobacterium, viruses, fungi and even parasites like Toxoplasma.
    The patient becomes so immuno-deficient that he/she cannot be protected against these infections. AIDS is diagnosed by ELISA; anti-retroviral drugs are only partially effective and can prolong life but not prevent death.

  2. Exercise 7.12

    How is a cancerous cell different from a normal cell?

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    A cancerous cell has lost contact inhibition and divides without control; in a normal cell, growth and differentiation are highly controlled and regulated.
    Contact inhibition — a normal cell stops its growth when it contacts other cells; the cancer cell appears to have lost this property and simply continues to divide, giving rise to masses of cells called tumors.
    Regulation — in cancer cells there is a breakdown of the regulatory mechanisms governing cell growth and differentiation.
    Invasion — malignant (neoplastic) cancer cells grow very rapidly, invading and damaging the surrounding normal tissues, and they starve the normal cells by competing for vital nutrients. Normal cells do neither.
    Metastasis — cells sloughed from a malignant tumor travel through the blood and start new tumors at distant sites; a normal cell stays in its own tissue.
    Origin — a normal cell becomes cancerous when carcinogens (physical, chemical or biological agents) act on it, or when cellular oncogenes (proto-oncogenes) already present in normal cells are activated.
    Immune behaviour — tumor cells carry cancer-specific antigens and have been shown to avoid detection and destruction by the immune system.

  3. Exercise 7.13

    Explain what is meant by metastasis.

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    Metastasis is the spread of cancer cells from the original tumor to distant sites in the body, where they start new tumors.
    Cells sloughed from a malignant tumor reach distant sites through the blood, and wherever they get lodged in the body, they start a new tumor there.
    It is a property of malignant tumors only. Benign tumors normally remain confined to their original location, do not spread to other parts of the body and cause little damage.
    The chapter calls it the most feared property of malignant tumors — it is what makes the disease impossible to remove by treating one site alone.

  4. Exercise 7.14

    List the harmful effects caused by alcohol/drug abuse.

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    The harmful effects run from immediate behavioural damage to death, and they reach the abuser's family as well.
    Immediate adverse effects — reckless behaviour, vandalism and violence.
    Excessive doses may lead to coma and death due to respiratory failure, heart failure or cerebral hemorrhage. A combination of drugs, or their intake along with alcohol, generally results in overdosing and even death.
    Warning signs in youth — drop in academic performance, unexplained absence from school/college, lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships with family and friends, loss of interest in hobbies, change in sleeping and eating habits, and fluctuations in weight and appetite.
    Social and family effects — an abuser unable to get money for drugs/alcohol may turn to stealing; the addict becomes a cause of mental and financial distress to the entire family and friends; dependence makes the person ignore all social norms to fund the habit.
    Infections — those who take drugs intravenously are much more likely to acquire AIDS and Hepatitis B through shared infected needles and syringes. Both are chronic and ultimately fatal.
    Long-term organ damage — chronic use of drugs and alcohol damages the nervous system and the liver (cirrhosis). Alcohol use during adolescence may lead to heavy drinking in adulthood.
    On the unborn child — use of drugs and alcohol during pregnancy adversely affects the foetus.
    Addiction and dependence themselves — a psychological attachment forms, tolerance rises, and abrupt stopping brings a withdrawal syndrome of anxiety, shakiness, nausea and sweating, which can be severe and even life-threatening.
    From misuse in sports (anabolic steroids) — in females, masculinisation, increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive facial and body hair, enlargement of the clitoris and deepening of the voice; in males, acne, increased aggressiveness, mood swings, depression, reduced testicle size, decreased sperm production, kidney and liver dysfunction, breast enlargement, premature baldness and enlargement of the prostate gland. In adolescents of either sex, severe facial and body acne and premature closure of the growth centres of the long bones, causing stunted growth. These effects may be permanent with prolonged use.

  5. Exercise 7.15

    Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?

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    Yes. The chapter lists peer pressure among the factors associated with drug and alcohol abuse in adolescents, alongside unstable or unsupportive family structures.
    Friends influence in two ways the chapter names — direct peer pressure, and the shared perception among youth that it is 'cool' or progressive to smoke, use drugs or alcohol, a perception that television, movies, newspapers and the internet help to promote.
    Adolescence is a very vulnerable phase of mental and psychological development, which is why influence works so strongly at this age.
    How one may protect oneself
    Avoid undue peer pressure — every child has his/her own choice and personality, which should be respected; do not let yourself be pushed beyond your threshold limits, in studies, sports or anything else.
    Education and counselling — learn to face problems and stresses and to accept disappointments and failures as a part of life; channelise your energy into healthy pursuits like sports, reading, music, yoga and other extracurricular activities.
    Seek help from parents and peers immediately, so that they can guide you; help may also be sought from close and trusted friends. This lets a young person vent feelings of anxiety and guilt.
    Look for danger signs — and if you find a friend using drugs or alcohol, do not hesitate to bring it to the notice of parents or a teacher, in the best interests of the person concerned.
    Seek professional and medical help — qualified psychologists, psychiatrists, and de-addiction and rehabilitation programmes are available.

  6. Exercise 7.16

    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.

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    Because of the inherent addictive nature of alcohol and drugs, which traps the user in a vicious circle of addiction and dependence.
    Addiction is a psychological attachment to certain effects — euphoria and a temporary feeling of well-being — associated with drugs and alcohol. These drive people to take them even when they are not needed, or even when their use becomes self-destructive.
    Tolerance rises. With repeated use, the tolerance level of the receptors in our body increases, so the receptors respond only to higher doses, leading to greater intake and deeper addiction.
    Even a single use can be a fore-runner to addiction — the chapter is explicit about this.
    Dependence then sets in: the body manifests a characteristic and unpleasant withdrawal syndrome if the regular dose is abruptly discontinued — anxiety, shakiness, nausea and sweating — which is relieved only when use is resumed. In some cases the withdrawal symptoms are severe and even life-threatening, needing medical supervision.
    In the absence of any guidance or counselling, the person gets addicted and becomes dependent, and dependence leads him/her to ignore all social norms to get funds for the habit.
    It is difficult, not impossible — with counselling, medical help, de-addiction and rehabilitation programmes, and sufficient effort and will power, the affected individual can get rid of the problem completely and lead a perfectly normal and healthy life.

  7. Exercise 7.17

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

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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.

    What motivates youngsters
    Curiosity, the need for adventure and excitement, and experimentation are the common causes. A child's natural curiosity motivates him/her to experiment.
    The perceived benefits of alcohol or drug use complicate this further — the first use may be out of curiosity, but later the child starts using these to escape facing problems.
    Stress, from pressures to excel in academics or examinations, has of late played a significant role in persuading youngsters to try alcohol and drugs.
    The perception that it is 'cool' or progressive to smoke, use drugs or alcohol — a perception that television, movies, newspapers and the internet help to promote.
    Unstable or unsupportive family structures and peer pressure.
    Adolescence itself (roughly $\displaystyle 12$–$\displaystyle 18$ years) is a very vulnerable phase of mental and psychological development, accompanied by several biological and behavioural changes.
    How it can be avoided
    Identify early the situations that may push an adolescent towards drugs or alcohol, and take remedial measures well in time. Parents and teachers have a special responsibility here; parenting that combines high levels of nurturance with consistent discipline is associated with a lowered risk of substance abuse.
    (i) Avoid undue peer pressure — respect and nurture the child's own choice and personality; do not push a child beyond his/her threshold limits in studies, sports or other activities.
    (ii) Education and counselling — teach the child to face problems and stresses and to accept disappointments and failures as a part of life; channelise the child's energy into healthy pursuits like sports, reading, music, yoga and other extracurricular activities.
    (iii) Seeking help from parents and peers — help should be sought immediately from parents, peers or close and trusted friends, which also lets the young person vent feelings of anxiety and guilt.
    (iv) Looking for danger signs — alert parents and teachers should watch for the warning signs; even friends should not hesitate to bring the matter to the notice of parents or teachers.
    (v) Seeking professional and medical help — qualified psychologists, psychiatrists, and de-addiction and rehabilitation programmes are available, and with them the affected individual can recover completely.