આ MCQ મોડ્યુલ આના પર આધારિત છે: Transport Regulation Disorders
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Transport Regulation Disorders
🎓 Class 11
Biology
CBSE
Theory
Ch 14 – Breathing and Exchange of Gases
⏱ ~14 min
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આ મૂલ્યાંકન આના પર આધારિત હશે: Transport Regulation Disorders
મૂલ્યાંકન બનાવવામાં તેમની સામગ્રી સામેલ કરવા ચિત્રો, PDF અથવા Word દસ્તાવેજ અપલોડ કરો.
Transport of Gases, Regulation of Respiration and Disorders
The gases have crossed the diffusion membrane. But dissolved gas alone could never meet the body's needs — plasma can hold far too little. This part follows the carriers that solve that problem, the brain centres that set the rhythm, and what goes wrong when the system fails.
14.4 Transport of Gases
Blood is the medium of transport for O₂ and CO₂. The division of labour is worth memorising as a set of figures, because examiners ask for them directly.
| Gas | Mode of transport | Share |
|---|---|---|
| O₂ | Transported by RBCs (as oxyhaemoglobin) | About 97 per cent |
| Carried in a dissolved state through the plasma | The remaining 3 per cent | |
| CO₂ | Transported by RBCs (as carbamino-haemoglobin) | Nearly 20–25 per cent |
| Carried as bicarbonate | 70 per cent | |
| Carried in a dissolved state through plasma | About 7 per cent |
14.4.1 Transport of Oxygen
Haemoglobin is a red coloured iron containing pigment present in the RBCs. O₂ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of O₂.
Binding of oxygen with haemoglobin is primarily related to the partial pressure of O₂. Partial pressure of CO₂, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.
The oxygen dissociation curve. A sigmoid curve is obtained when percentage saturation of haemoglobin with O₂ is plotted against the pO₂. This curve is called the Oxygen dissociation curve and is highly useful in studying the effect of factors like pCO₂, H⁺ concentration, etc., on binding of O₂ with haemoglobin.
The four conditions, compared at the two sites
| Condition | In the alveoli | In the tissues |
|---|---|---|
| pO₂ | High | Low |
| pCO₂ | Low | High |
| H⁺ concentration | Lesser | High |
| Temperature | Lower | Higher |
| Net result | All factors favourable for the formation of oxyhaemoglobin | Conditions favourable for dissociation of oxygen from oxyhaemoglobin |
This clearly indicates that O₂ gets bound to haemoglobin in the lung surface and gets dissociated at the tissues. Every 100 mL of oxygenated blood can deliver around 5 mL of O₂ to the tissues under normal physiological conditions.
What makes this elegant. Notice that all four conditions shift together, and all four push the same way. A tissue that is working hard is by that very fact low in O₂, high in CO₂, acidic and warm — so the harder a tissue works, the more readily haemoglobin surrenders its oxygen to it. No nerve, no hormone and no enzyme is involved. The delivery is self-regulating, built into the chemistry of one molecule.
Why the curve is sigmoid, not a straight line. The reason lies in the sentence that each haemoglobin molecule can carry a maximum of four molecules of O₂. The four binding sites do not act independently: once the first O₂ attaches, the molecule changes shape so that the next one binds more readily, and so on. This is cooperative binding. It produces a shallow start, a steep middle and a flat top — and that shape is exactly what is useful. The flat upper plateau means haemoglobin loads to nearly full saturation in the lungs even if alveolar pO₂ falls somewhat, as at altitude. The steep middle, which is where tissue pO₂ of 40 lies, means a small further fall in pO₂ releases a large amount of oxygen exactly where it is needed.
14.4.2 Transport of Carbon dioxide
Mode 1 — carbamino-haemoglobin (20–25%)
CO₂ is carried by haemoglobin as carbamino-haemoglobin (about 20–25 per cent). This binding is related to the partial pressure of CO₂. pO₂ is a major factor which could affect this binding.
- When pCO₂ is high and pO₂ is low, as in the tissues, more binding of carbon dioxide occurs.
- When the pCO₂ is low and pO₂ is high, as in the alveoli, dissociation of CO₂ from carbamino-haemoglobin takes place — i.e., CO₂ which is bound to haemoglobin from the tissues is delivered at the alveoli.
Mode 2 — bicarbonate (70%)
RBCs contain a very high concentration of the enzyme carbonic anhydrase, and minute quantities of the same is present in the plasma too. This enzyme facilitates the following reaction in both directions.
CO2 + H2O ⇆ carbonic anhydrase ⇆ H2CO3 ⇆ HCO3− + H+
- At the tissue site, where partial pressure of CO₂ is high due to catabolism, CO₂ diffuses into blood (RBCs and plasma) and forms HCO₃⁻ and H⁺.
- At the alveolar site, where pCO₂ is low, the reaction proceeds in the opposite direction, leading to the formation of CO₂ and H₂O.
Thus CO₂ trapped as bicarbonate at the tissue level and transported to the alveoli is released out as CO₂. Every 100 mL of deoxygenated blood delivers approximately 4 mL of CO₂ to the alveoli.
Mode 3 — dissolved in plasma (7%)
The remaining about 7 per cent of CO₂ is carried in a dissolved state through plasma — possible only because CO₂ is so much more soluble than O₂, which manages only 3 per cent this way.
The linked pair worth noticing. Each gas helps unload the other. High pCO₂ in the tissues promotes dissociation of O₂ from oxyhaemoglobin, and at the same time low pO₂ in the tissues promotes binding of CO₂ as carbamino-haemoglobin. At the alveoli both reverse together. One molecule, two passengers, and each passenger's arrival helps the other leave.
14.5 Regulation of Respiration
Human beings have a significant ability to maintain and moderate the respiratory rhythm to suit the demands of the body tissues. This is done by the neural system.
| Structure | Location | Role |
|---|---|---|
| Respiratory rhythm centre | Medulla region of the brain | Primarily responsible for this regulation |
| Pneumotaxic centre | Pons region of the brain | Can moderate the functions of the respiratory rhythm centre. Its neural signal can reduce the duration of inspiration and thereby alter the respiratory rate |
| Chemosensitive area | Adjacent to the rhythm centre | Highly sensitive to CO₂ and hydrogen ions. Increase in these can activate this centre, which signals the rhythm centre to make necessary adjustments by which these substances can be eliminated |
| Receptors of the aortic arch and carotid artery | Great vessels | Can recognise changes in CO₂ and H⁺ concentration and send necessary signals to the rhythm centre for remedial actions |
The fact students find counter-intuitive. The role of oxygen in the regulation of respiratory rhythm is quite insignificant. Breathing is regulated by CO₂ and H⁺, not by oxygen. Every receptor named above monitors CO₂ and hydrogen ions; not one monitors O₂ as its primary signal.
14.6 Disorders of Respiratory System
Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
Emphysema is a chronic disorder in which alveolar walls are damaged, due to which respiratory surface is decreased. One of the major causes of this is cigarette smoking.
Occupational Respiratory Disorders. In certain industries, especially those involving grinding or stone-breaking, so much dust is produced that the defense mechanism of the body cannot fully cope with the situation. Long exposure can give rise to inflammation leading to fibrosis (proliferation of fibrous tissues) and thus causing serious lung damage. Workers in such industries should wear protective masks.
Each disorder attacks a different part of the machinery. Put beside the earlier parts of the chapter, the three disorders map onto three different steps. Asthma damages the conducting part — inflamed bronchi and bronchioles obstruct air flow, so ventilation suffers while the exchange surface is intact. Emphysema destroys the exchange part — area is lost, not airway width, which is why opening the airways does not relieve it. Fibrosis thickens the diffusion membrane, whose total thickness is normally much less than a millimetre. Reading the disorders this way turns three definitions into one coherent picture.
📐 Activity 14.4 — Read the oxygen dissociation curve
What to do. Draw the axes for Figure 14.5 on graph paper: pO₂ from 0 to 100 mm Hg on the x-axis, percentage saturation of haemoglobin from 0 to 100 on the y-axis. Sketch the sigmoid curve. Now mark two points on it: A at the alveolar pO₂ of 104, and T at the tissue pO₂ of 40. Read off the approximate saturation at each, and calculate the difference.
Then, on the same axes, sketch a second curve shifted to the right, as it would be under tissue conditions of high pCO₂, high H⁺ concentration and higher temperature, and read off the saturation at pO₂ 40 again.
Predict: is haemoglobin nearly empty at tissue pO₂, or still largely loaded? And does the rightward shift help or hinder the tissues?
Readings. At point A (pO₂ 104) haemoglobin is about 97 per cent saturated. At point T (pO₂ 40) it is still roughly 75 per cent saturated. The difference of about 22 per cent is the oxygen actually handed over — which matches the chapter's figure that every 100 mL of oxygenated blood can deliver around 5 mL of O₂ to the tissues under normal physiological conditions.
The surprise. Haemoglobin is not emptied at the tissues. It leaves with three-quarters of its oxygen still bound. That reserve is what a muscle draws on when it starts to work hard — a small extra fall in tissue pO₂ then releases a great deal more oxygen, because pO₂ 40 sits on the steep part of the curve.
The rightward shift helps the tissues. Under tissue conditions — low pO₂, high pCO₂, high H⁺ concentration and higher temperature — the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin. On the shifted curve, saturation at pO₂ 40 falls well below 75 per cent, so more oxygen is released at the same pO₂. The beauty of it: an active tissue generates exactly those four conditions by working, so it summons its own extra oxygen supply automatically.
Why the plateau matters too. The flat top means that even if alveolar pO₂ drops appreciably — at altitude, or in mild lung disease — haemoglobin still loads to near-full saturation. The curve's shape gives safety in loading and sensitivity in unloading, which a straight line could not do.
🎯 Interactive: Change a condition, predict the effect
Effect on O₂–haemoglobin binding: Favours formation of oxyhaemoglobin
Binding of oxygen with haemoglobin is primarily related to the partial pressure of O2. In the alveoli, where pO2 is high, pCO2 low, H+ concentration lesser and temperature lower, all the factors are favourable for the formation of oxyhaemoglobin.
🎯 Competency-Based Questions
Scenario: A sprinter finishes a 400 m race. Her muscle temperature has risen, her muscles are producing lactic acid, her muscle pCO₂ is high and her muscle pO₂ has fallen below 20 mm Hg. Meanwhile a patient in another ward has been given a drug that inhibits carbonic anhydrase, and a third patient has been breathing a gas mixture with an abnormally high CO₂ content.
Q1. Explain, using all four factors, why the sprinter's muscles receive far more oxygen than at rest. L4 Analyse
All four of the chapter's factors have shifted in the direction that favours dissociation of oxygen from oxyhaemoglobin, and they act together. (i) pO₂ is low — below 20 mm Hg, further down the steep part of the dissociation curve than the usual 40, so a much larger share of the bound oxygen is released. (ii) pCO₂ is high, from vigorous catabolism. (iii) H⁺ concentration is high, from the lactic acid. (iv) Temperature is higher, from the heat of respiration. The chapter states that in the tissues, where low pO₂, high pCO₂, high H⁺ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin. The elegance is that the muscle creates all four conditions simply by working hard, so the extra oxygen is summoned automatically, with no nerve or hormone involved.
Q2. Predict the effect of inhibiting carbonic anhydrase on CO₂ transport. L3 Apply
The largest route for CO₂ would be crippled. Nearly 70 per cent of CO₂ is carried as bicarbonate, and it is carbonic anhydrase — present in very high concentration in RBCs — that facilitates the reaction CO₂ + H₂O ⇆ H₂CO₃ ⇆ HCO₃⁻ + H⁺ in both directions. Without the enzyme, CO₂ arriving at the tissues could not be rapidly trapped as bicarbonate, and what bicarbonate did exist could not be rapidly reconverted at the alveoli. Only the other two routes would remain — 20–25 per cent as carbamino-haemoglobin and about 7 per cent dissolved in plasma — so CO₂ would accumulate in the tissues and blood.
Q3. Fill in the blanks: About ______ per cent of O₂ is transported by RBCs and ______ per cent dissolved in plasma. Of CO₂, ______ per cent travels as bicarbonate, ______ per cent bound to haemoglobin and ______ per cent dissolved in plasma. L1 Remember
97; 3; 70; 20–25; about 7.
Q4. The third patient, breathing CO₂-rich gas, begins to breathe deeply and rapidly although his blood oxygen is normal. Explain the mechanism. L4 Analyse
Because respiration is regulated by carbon dioxide, not oxygen. The inhaled CO₂ raises blood pCO₂, and since CO₂ + H₂O ⇆ H₂CO₃ ⇆ HCO₃⁻ + H⁺, the H⁺ concentration rises with it. A chemosensitive area situated adjacent to the rhythm centre is highly sensitive to CO₂ and hydrogen ions; an increase in these substances can activate this centre, which in turn can signal the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated. In parallel, receptors associated with the aortic arch and carotid artery also recognise changes in CO₂ and H⁺ concentration and send necessary signals to the rhythm centre for remedial actions. The respiratory rhythm centre in the medulla then raises rate and depth to blow the CO₂ off. The patient's normal oxygen is beside the point, because the role of oxygen in the regulation of respiratory rhythm is quite insignificant.
Q5. “We breathe because our body detects that it is running short of oxygen.” Evaluate this common belief. L5 Evaluate
The belief is intuitive and largely incorrect, and the chapter says so in a single sentence: the role of oxygen in the regulation of respiratory rhythm is quite insignificant.
What actually drives breathing. Every regulating structure the chapter names monitors CO₂ and hydrogen ions: the chemosensitive area adjacent to the rhythm centre is highly sensitive to CO₂ and hydrogen ions, and the receptors associated with the aortic arch and carotid artery also recognise changes in CO₂ and H⁺ concentration. The respiratory rhythm centre in the medulla then adjusts respiration so that these substances can be eliminated. Not one of them is described as primarily an oxygen sensor.
Why this design makes sense. CO₂ is the better signal on three counts. It is produced in proportion to metabolic rate, so it reports demand directly. It is 20–25 times more soluble than O₂ and converts to H⁺, so a small change is easy to detect chemically. And because of the flat upper plateau of the oxygen dissociation curve, haemoglobin stays about 97 per cent saturated even when alveolar pO₂ falls appreciably — so oxygen saturation is a late and insensitive warning, whereas CO₂ changes early.
The grain of truth. Oxygen is not entirely without influence — it becomes a significant stimulus in severe hypoxia, and at high altitude the fall in atmospheric pO₂ does eventually drive increased ventilation. So the honest verdict: breathing is normally regulated by carbon dioxide and hydrogen ions, with oxygen serving only as an emergency backup. The common belief mistakes the ultimate purpose of breathing for its actual control signal.
What actually drives breathing. Every regulating structure the chapter names monitors CO₂ and hydrogen ions: the chemosensitive area adjacent to the rhythm centre is highly sensitive to CO₂ and hydrogen ions, and the receptors associated with the aortic arch and carotid artery also recognise changes in CO₂ and H⁺ concentration. The respiratory rhythm centre in the medulla then adjusts respiration so that these substances can be eliminated. Not one of them is described as primarily an oxygen sensor.
Why this design makes sense. CO₂ is the better signal on three counts. It is produced in proportion to metabolic rate, so it reports demand directly. It is 20–25 times more soluble than O₂ and converts to H⁺, so a small change is easy to detect chemically. And because of the flat upper plateau of the oxygen dissociation curve, haemoglobin stays about 97 per cent saturated even when alveolar pO₂ falls appreciably — so oxygen saturation is a late and insensitive warning, whereas CO₂ changes early.
The grain of truth. Oxygen is not entirely without influence — it becomes a significant stimulus in severe hypoxia, and at high altitude the fall in atmospheric pO₂ does eventually drive increased ventilation. So the honest verdict: breathing is normally regulated by carbon dioxide and hydrogen ions, with oxygen serving only as an emergency backup. The common belief mistakes the ultimate purpose of breathing for its actual control signal.
🧠 Assertion–Reason Questions
For each pair choose: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true but R is false. (D) A is false but R is true.
Assertion (A): Oxygen is released from oxyhaemoglobin at the tissues.
Reason (R): In the tissues, low pO₂, high pCO₂, high H⁺ concentration and higher temperature all favour dissociation of oxygen from oxyhaemoglobin.
Answer: A. Both are true and the reason is the correct explanation. All four conditions shift together and all four push the same way.
Assertion (A): Respiratory rhythm is primarily regulated by the partial pressure of oxygen in the blood.
Reason (R): A chemosensitive area adjacent to the rhythm centre is highly sensitive to CO₂ and hydrogen ions.
Answer: D. The assertion is false — the role of oxygen in the regulation of respiratory rhythm is quite insignificant. The reason is true and names the actual signals: CO₂ and H⁺.
Assertion (A): Most of the carbon dioxide in blood travels as bicarbonate rather than as a gas.
Reason (R): RBCs contain a very high concentration of carbonic anhydrase, which facilitates the interconversion of CO₂ and water with carbonic acid and bicarbonate in both directions.
Answer: A. Both are true and the reason explains the assertion. Nearly 70 per cent of CO₂ is carried as bicarbonate, which is possible only because the enzyme makes the conversion fast enough in both directions.
Coming next. Part 5 is the exercise part: the chapter summary followed by full worked solutions to all fourteen NCERT exercise questions of Chapter 14, including the three “distinguish between” pairs, the multiple-choice question on partial pressures, and the questions on hypoxia and climbing a hill.
Frequently Asked Questions - Transport of Gases, Regulation and Disorders
How is oxygen transported in blood?
About 97 per cent of O2 is transported by RBCs bound reversibly to haemoglobin as oxyhaemoglobin, each haemoglobin molecule carrying a maximum of four O2 molecules. The remaining 3 per cent is carried in a dissolved state through the plasma.
What is the oxygen dissociation curve?
It is the sigmoid curve obtained when the percentage saturation of haemoglobin with O2 is plotted against pO2. It is highly useful in studying the effect of factors such as pCO2 and H+ concentration on the binding of O2 with haemoglobin.
Why is the oxygen dissociation curve sigmoid?
Because each haemoglobin molecule carries up to four O2 molecules and the binding sites do not act independently - binding of the first oxygen makes the next bind more readily. This cooperative binding gives a shallow start, a steep middle and a flat plateau, which means near-full loading in the lungs and sensitive unloading at the tissues.
Which conditions favour oxyhaemoglobin formation and which favour dissociation?
In the alveoli high pO2, low pCO2, lesser H+ concentration and lower temperature all favour the formation of oxyhaemoglobin. In the tissues low pO2, high pCO2, high H+ concentration and higher temperature favour dissociation of oxygen from oxyhaemoglobin.
What are the major transport mechanisms for carbon dioxide?
Nearly 70 per cent is carried as bicarbonate, formed with the help of carbonic anhydrase; about 20 to 25 per cent is carried by haemoglobin as carbamino-haemoglobin; and about 7 per cent is carried dissolved in plasma.
What is the role of carbonic anhydrase?
It is present in very high concentration in RBCs and in minute quantities in plasma, and it facilitates the reaction CO2 + H2O giving H2CO3 and then HCO3 minus plus H plus, in both directions. At the tissues it traps CO2 as bicarbonate; at the alveoli the reaction reverses and CO2 is released.
How much O2 and CO2 are delivered per 100 mL of blood?
Every 100 mL of oxygenated blood can deliver around 5 mL of O2 to the tissues under normal physiological conditions, and every 100 mL of deoxygenated blood delivers approximately 4 mL of CO2 to the alveoli.
How is respiration regulated?
By the neural system. The respiratory rhythm centre in the medulla is primarily responsible. The pneumotaxic centre in the pons can moderate it by reducing the duration of inspiration. A chemosensitive area adjacent to the rhythm centre is highly sensitive to CO2 and hydrogen ions, and receptors in the aortic arch and carotid artery also detect these and signal the rhythm centre.
Does oxygen regulate the respiratory rhythm?
No. The role of oxygen in the regulation of respiratory rhythm is quite insignificant. Breathing is regulated by carbon dioxide and hydrogen ions, detected by the chemosensitive area and by receptors in the aortic arch and carotid artery.
What are the main disorders of the respiratory system?
Asthma, a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. Emphysema, a chronic disorder in which alveolar walls are damaged so the respiratory surface is decreased, cigarette smoking being a major cause. And occupational respiratory disorders, in which long exposure to dust in grinding or stone-breaking industries causes inflammation leading to fibrosis and serious lung damage.
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