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NCERT Solutions · Class 11 Biology Breathing and Exchange of Gases

14 questions · 14 still being checked

Exercises 14.11–14.14 (part 2 of 2)

  1. Exercise 14.11

    Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?

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    Definition
    The oxygen dissociation curve is the sigmoid curve obtained when the percentage saturation of haemoglobin with \(\displaystyle O_{2} \) is plotted against the partial pressure of oxygen, \(\displaystyle pO_{2} \).
    It is highly useful in studying the effect of factors like \(\displaystyle pCO_{2} \), \(\displaystyle H^{+} \) concentration and temperature on the binding of \(\displaystyle O_{2} \) with haemoglobin.
    It shows that in the alveoli — high \(\displaystyle pO_{2} \), low \(\displaystyle pCO_{2} \), lesser \(\displaystyle H^{+} \), lower temperature — oxyhaemoglobin forms, while in the tissues — low \(\displaystyle pO_{2} \), high \(\displaystyle pCO_{2} \), high \(\displaystyle H^{+} \), higher temperature — oxygen dissociates from it.
    Why sigmoid, as far as the chapter allows
    Each haemoglobin molecule can carry a maximum of four molecules of \(\displaystyle O_{2} \), and they are taken up one after another, so saturation cannot rise as a straight line with \(\displaystyle pO_{2} \).
    The usual explanation is that the binding of the first \(\displaystyle O_{2} \) makes it easier for the next to bind (co-operative binding), giving the steep middle portion, while the curve flattens at high \(\displaystyle pO_{2} \) because all four sites are nearly filled.
    NCERT_Solution_Class11_Biology_Ch14_Q14-11

  2. Exercise 14.12

    Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.

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    Hypoxia is a condition in which the oxygen reaching the body tissues falls short of what they need for normal metabolism — a definition brought in from outside, because Chapter $\displaystyle 14$ prints the word only in this exercise and never defines it.
    Its usual types, also from outside the chapter:
    Hypoxic hypoxia — the arterial \(\displaystyle pO_{2} \) itself is low, as in the thin air of high altitude or where a lung disorder spoils diffusion.
    Anaemic hypoxia — enough oxygen reaches the lungs, but too little functional haemoglobin is present to carry it.
    Stagnant hypoxia — the blood carries oxygen normally but circulates too sluggishly to deliver it.
    Histotoxic hypoxia — oxygen is delivered to the cells, but they cannot use it.
    Common signs are breathlessness, faster breathing and heart rate, headache, fatigue and confusion, and a bluish tinge of the skin and lips (cyanosis).
    What the chapter supplies for the discussion:
    It sets out what a normal oxygen supply depends on: a \(\displaystyle pO_{2} \) gradient of $\displaystyle 104$ mm Hg in the alveoli against $\displaystyle 40$ mm Hg in deoxygenated blood, a diffusion membrane much thinner than a millimetre, and haemoglobin in the RBCs to carry about $\displaystyle 97$ per cent of the \(\displaystyle O_{2} \).
    Anything that spoils one of these would leave the tissues short of oxygen. The chapter names three such conditions:
    Emphysema — alveolar walls are damaged and the respiratory surface is decreased; cigarette smoking is a major cause.
    Asthma — difficulty in breathing with wheezing, due to inflammation of the bronchi and bronchioles.
    Occupational respiratory disorders — long exposure to dust in grinding or stone-breaking industries causes inflammation and fibrosis, seriously damaging the lung.
    Tie the two together while discussing: emphysema and occupational fibrosis shrink the exchange surface, asthma obstructs the air passages, and a shortage of haemoglobin cripples the $\displaystyle 97$ per cent of \(\displaystyle O_{2} \) the RBCs carry — each one a route to the oxygen shortage defined above.

  3. Exercise 14.13

    Distinguish between
    (a)
    IRV and ERV
    (b)
    Inspiratory capacity and Expiratory capacity.
    (c)
    Vital capacity and Total lung capacity.

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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) IRV and ERV
    Inspiratory Reserve Volume (IRV) is the additional volume of air a person can inspire by a forcible inspiration, over and above a normal inspiration. It averages $\displaystyle 2500$ mL to $\displaystyle 3000$ mL.
    Expiratory Reserve Volume (ERV) is the additional volume of air a person can expire by a forcible expiration, over and above a normal expiration. It averages $\displaystyle 1000$ mL to $\displaystyle 1100$ mL.
    So IRV concerns the extra air taken in, ERV the extra air pushed out, and IRV is the larger of the two.
    (b) Inspiratory capacity and Expiratory capacity
    Inspiratory Capacity (IC) is the total volume of air a person can inspire after a normal expiration: \(\displaystyle \text{IC} = \text{TV} + \text{IRV} \), about $\displaystyle 3000$–$\displaystyle 3500$ mL.
    Expiratory Capacity (EC) is the total volume of air a person can expire after a normal inspiration: \(\displaystyle \text{EC} = \text{TV} + \text{ERV} \), about $\displaystyle 1500$–$\displaystyle 1600$ mL.
    Both include the tidal volume, but IC adds the inspiratory reserve while EC adds the expiratory reserve.
    (c) Vital capacity and Total lung capacity
    Vital Capacity (VC) is the maximum volume of air a person can breathe in after a forced expiration: \(\displaystyle \text{VC} = \text{ERV} + \text{TV} + \text{IRV} \), about $\displaystyle 4000$–$\displaystyle 4600$ mL.
    Total Lung Capacity (TLC) is the total volume of air accommodated in the lungs at the end of a forced inspiration: \(\displaystyle \text{TLC} = \text{RV} + \text{ERV} + \text{TV} + \text{IRV} = \text{VC} + \text{RV} \), about $\displaystyle 5100$–$\displaystyle 5800$ mL.
    The one difference is the residual volume ($\displaystyle 1100$–$\displaystyle 1200$ mL): TLC includes it, VC does not, because that air remains in the lungs even after a forcible expiration and can never be breathed out.

  4. Exercise 14.14

    What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.

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    Tidal Volume (TV) is the volume of air inspired or expired during a normal respiration. It is approximately $\displaystyle 500$ mL.
    Tidal volume in an hour
    A healthy human breathes $\displaystyle 12$–$\displaystyle 16$ times per minute, so per minute the volume is \(\displaystyle 500\ \text{mL} \times 12\text{–}16 = 6000\text{–}8000\ \text{mL} \), which is the figure the chapter itself gives.
    In one hour: \(\displaystyle 6000\text{–}8000\ \text{mL} \times 60 = 3{,}60{,}000\text{–}4{,}80{,}000\ \text{mL} \).
    That is about $\displaystyle 360$ to $\displaystyle 480$ litres of air per hour.