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NCERT Exemplar · Class 9 Science Why Do We Fall Ill

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Long Answer Questions 30–39 (part 4 of 4)

  1. Exercise 30

    Explain giving reasons
    (a)
    Balanced diet is necessary for maintaining healthy body.
    (b)
    Health of an organism depends upon the surrounding environmental
    conditions.
    (c)
    Our surrounding area should be free of stagnant water.
    (d)
    Social harmony and good economic conditions are necessary for good
    health.

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    NCERT’s answer
    (a)
    Food is necessary for the growth and development of the body. Balanced diet provides raw materials and energy in appropriate amount needed for the substances likes protein, carbohydrates, fats, minerals etc which in turn are essential for the proper growth and functioning of the healthy body. (b) Health is a state of being well enough to function well physically, mentally and socially and these conditions depend upon the surrounding environmental conditions. eg., If there is unhygienic conditions in surrounding area, it is likely we might get infected or diseased. (c) This is so because many water borne diseases and insect vectors flourish in stagnant water which cause diseases in human beings. (d) Human beings live in societies and different localities like villages or cities, which determines the social and physical environment and hence both are to be kept in harmony. Public cleanliness is important for individual health. For better living conditions lot of money is required. We need good food for healthy body and for this we have to earn more. For the treatment of diseases also, one has to be in good economic condition.
    (a)
    Carbohydrates and fats supply energy, and proteins, vitamins and minerals supply the raw material for tissue repair and antibody production, so \(\displaystyle \text{poor diet} \Rightarrow \text{weak immunity} \Rightarrow \text{frequent illness}\).
    (b)
    Air, water and soil quality set how many pathogens and pollutants the body meets, so surroundings decide disease exposure as much as the body's own state.
    (c)
    \(\displaystyle \text{stagnant water} \Rightarrow \text{mosquito breeding} \Rightarrow \text{malaria, dengue, filariasis}\); removing it cuts the vector's life cycle at its source.
    (d)
    Money buys good food, clean water and treatment, and public cleanliness needs cooperation among neighbours, so \(\displaystyle \text{poverty or discord} \Rightarrow \text{malnutrition, unsafe surroundings, no care} \Rightarrow \text{poor health}\).
    Answer: diet, surroundings, standing water and social/economic conditions each control a different route by which disease reaches or overpowers the body.

  2. Exercise 31

    What is a disease? How many types of diseases have you studied? Give examples.

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    NCERT’s answer
    Hint— When the functioning or the appearance of one or more systems of the body change for the worse the body is said to be diseased. The diseases can be — acute/chronic/ infectious/non infectious. Examples, influenza, tuberculosis, pneumonia, cancer respectively.
    A disease is any deviation from normal body structure or function that produces recognisable signs, with or without an obvious external cause. By duration: acute — short-lived, e.g. common cold, typhoid; chronic — lasts long, sometimes lifelong, e.g. elephantiasis, tuberculosis. By cause: infectious — due to a microbial agent and transmissible, e.g. cold, tuberculosis, AIDS; non-infectious — due to internal or environmental factors, not transmitted, e.g. cancer, high blood pressure, deficiency diseases.Answer: disease is a disturbance of normal body function; it is studied along two axes — acute/chronic by duration, infectious/non-infectious by cause.

  3. Exercise 32

    What do you mean by disease symptoms? Explain giving two examples?

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    NCERT’s answer
    When the functioning or the appearance of one or more systems of the body will change for the worse, it gives certain abnormal signs of the disease. These visual changes in human beings are called symptoms. Symptoms give indication of the presence of a particular disease. Example (i) Lesions on the skin are the symptoms of chickenpox. Example (ii) Cough is the symptom of lung infection.
    Symptoms are the outward signs that tell us a body is diseased — they show that something is wrong, though not always which disease it is.Skin lesions over the whole body — a symptom of chickenpox. Cough with fever — a symptom of a lung infection.Answer: symptoms are visible signs that a disease is present, e.g. skin lesions (chickenpox) and cough with fever (lung infection).

  4. Exercise 33

    Why is immune system essential for our health?

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    NCERT’s answer
    The immune system of our body is a kind of defense mechanism to fight against pathogenic microbes. It has cells that are specialized to kill infecting microbes and keep our body healthy.
    The immune system is the body's defence network — skin and mucus as physical barriers, plus phagocytic and antibody-producing cells inside — that meets an invading pathogen before it can multiply. \(\displaystyle \text{pathogen entry} \Rightarrow \text{immune recognition} \Rightarrow \text{destruction/neutralisation} \Rightarrow \text{no disease}\) When it is weak — from malnutrition, HIV infection or drugs that suppress it — even a mild pathogen multiplies unchecked and a minor infection turns severe.Answer: the immune system detects and destroys pathogens before they establish infection, so its strength directly decides whether exposure to a pathogen ends in disease.

  5. Exercise 34

    What precautions will you take to justify “prevention is better than cure”.

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    NCERT’s answer
    Following precautions should be taken for prevention of disease. ($\displaystyle 1$) Maintaining hygienic conditions. ($\displaystyle 2$) Awareness about the disease and causal organism. ($\displaystyle 3$) Balanced diet. ($\displaystyle 4$) Regular medical check up.
    A balanced diet keeps the body's own defences strong; personal hygiene and clean drinking water stop pathogens from entering it in the first place. Keep surroundings free of stagnant water and garbage, with proper waste disposal — this denies mosquitoes and other vectors a breeding site. Stay up to date on immunisation against preventable diseases and go for regular medical check-ups to catch problems early. Stay aware of disease outbreaks around you and keep distance from a person with an infectious illness.Answer: diet and hygiene, clean surroundings, timely immunisation with regular check-ups, and awareness of disease around you each block one route to illness — far cheaper than treating it after it strikes.

  6. Exercise 35

    Why do some children fall ill more frequently than others living in the same locality?

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    NCERT’s answer
    Hint— Due to poor immune system, some children fall ill frequently. Balanced diet and proper nutrition for healthy body is required to have a strong immune system.
    Susceptibility differs child to child even within one locality:
    Nutrition — a poorly fed child has weaker immunity.
    Immunisation status — a vaccinated child carries acquired resistance an unvaccinated one lacks.
    Genetic make-up — inborn resistance to a given microbe varies between individuals.
    Hygiene habits — fewer microbes reach a child who washes hands and eats covered food.
    An existing illness — leaves less immune capacity to fight a new infection.
    Access to clean water and healthcare — can differ house to house even in one street.
    Answer: differences in nutrition, immunisation, genetic resistance, personal hygiene, existing illness and access to clean water/healthcare.

  7. Exercise 36

    Why are antibiotics not effective for viral disease?

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    NCERT’s answer
    Antibiotics generally block the biosynthetic pathways and they block these pathways of the microbes/bacteria. However, viruses have very few biochemical mechanisms of their own and hence are unaffected by antibiotics.
    Antibiotics work by blocking a bacteria-specific step — cell-wall synthesis or the bacterial ribosome — that only a bacterial cell carries.\[\text{virus has no cell wall or ribosomes of its own} \Rightarrow \text{it hijacks the host cell's machinery to replicate} \Rightarrow \text{no bacteria-specific target exists inside it} \]With no such target, the antibiotic has nothing to block.Answer: antibiotics act on bacterial cell-wall/ribosome machinery; a virus has none of its own, so no antibiotic target exists inside it.

  8. Exercise 37

    Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. Explain.

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    NCERT’s answer
    Because of strong immune system our body is normally fighting off microbes. We have cells which are specialised to kill the pathogenic microbes. These cells are active when infecting microbes enter the body and if they are successful in removing the pathogen, we remain disease- free. So even if we are exposed to infectious microbes, it is not necessary that we suffer from diseases.
    Exposure only starts a contest between the microbe and the host's own defences; disease is not automatic.\[\text{host immunity and nutrition} \uparrow \;\Rightarrow\; \text{microbe cleared before damage} \;\Rightarrow\; \text{no noticeable disease} \] \[\text{microbe number and virulence} \uparrow \;\Rightarrow\; \text{host defences overwhelmed} \;\Rightarrow\; \text{noticeable disease} \]A small infecting dose, a weak strain, prior immunity (from past infection or vaccination), or good nutrition can let the immune system clear the microbe silently.Answer: the outcome depends on the microbe's number/virulence versus the host's immunity and nutrition; the body can clear a small or weak infection without visible disease.

  9. Exercise 38

    Give any four factors necessary for a healthy person.

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    NCERT’s answer
    For a healthy person it is necessary that (i) The surrounding environment should be clean. Air and water borne diseases will not spread. (ii) Personal hygiene prevents infectious diseases. (iii) Proper, sufficient nourishment and food is necessary for good immune system of our body. (iv) Immunisation against severe diseases.
    Balanced, nutritious diet — builds the body's resistance to infection.
    Clean drinking water and proper sanitation — cuts exposure to disease-causing microbes.
    Timely immunisation and access to healthcare — prevents and treats disease early.
    A safe, secure social and economic environment — supports both physical and mental well-being.
    Answer: good nutrition; clean water and sanitation; immunisation and healthcare access; a safe, secure social-economic environment.

  10. Exercise 39

    Why is AIDS considered to be a ‘Syndrome’ and not a disease?

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    NCERT’s answer
    AIDS causing virus— HIV that comes into the body via, the sexual organs or any other means like blood transfusion will spread to lymph nodes all over the body. The virus damages the immune system of the body and due to this the body can no longer fight off many minor infections. Instead, every small cold can become pneumonia, or minor gut infection can become severe diarrhoea with blood loss. The effect of disease becomes very severe and complex, at times killing the person suffering from AIDS. Hence there is no specific disease symptoms for AIDS but it results in a complex diseases and symptoms. Therefore, it is known as a syndrome.
    A syndrome is a group of different signs and symptoms that appear together from one underlying cause, unlike a disease with one fixed, defined set of symptoms.HIV progressively destroys the immune system's helper T-cells, so the body loses its defence against many, unrelated microbes at once. Different patients then develop different combinations of infections and symptoms — tuberculosis, pneumonia, skin and gut infections, weight loss — depending on whichever opportunistic microbe finds the weakened immunity first.Answer: AIDS is a collection of varying symptoms/infections caused by HIV-driven immune collapse, not one specific disease — hence 'Acquired ImmunoDeficiency Syndrome'.