Q.A rise in blood CO2 concentration, a rise in H+ concentration (fall in pH), and a rise in temperature all shift the oxyhaemoglobin dissociation curve to the right, an effect known as the:
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Transport Of Oxygen
The Delivery Problem
Every one of the body's trillions of cells constantly burns fuel and needs a steady oxygen supply, yet oxygen is a gas and the cells are buried deep inside tissues. The body solves this with a dedicated carrier: a protein inside red blood cells called haemoglobin. Oxygen is not simply dissolved in blood — dissolved oxygen alone could barely supply the body — instead it binds chemically to haemoglobin, forming oxyhaemoglobin, which raises blood's oxygen-carrying capacity roughly seventy-fold.
How the Binding Works
When you inhale, oxygen diffuses from the alveoli into the surrounding capillaries and meets red blood cells packed with haemoglobin. Each haemoglobin molecule carries four iron-containing haem groups, and each haem group can bind one oxygen molecule. The reaction is reversible: haemoglobin picks up oxygen (Hb + 4 O₂ ⇌ Hb(O₂)₄) where oxygen is plentiful, in the lungs, and releases it where oxygen is scarce, in the tissues.
Oxyhaemoglobin, the oxygen-loaded form, is bright red; deoxyhaemoglobin, the oxygen-free form, is darker — this is why arterial blood looks bright red and venous blood looks darker.
Cooperative Binding
When the first oxygen molecule binds to haemoglobin, it triggers a shape change that makes it easier for the next three to bind — this is cooperative binding, and it produces an S-shaped (sigmoid) oxygen-haemoglobin dissociation curve rather than a straight line. At the oxygen level found in the lungs, haemoglobin is nearly fully saturated — almost every binding site is filled. At the lower oxygen level found in resting tissues, saturation drops to around 75%, meaning about a quarter of the carried oxygen is unloaded to the cells.
A healthy adult's blood carries about 20 mL of oxygen per 100 mL of blood; only a small fraction of that travels dissolved in plasma, the rest is bound to haemoglobin.
What Shifts the Curve
Haemoglobin's affinity for oxygen is not fixed — it changes with conditions in the tissues, letting the body fine-tune delivery:
| Factor | Change | Effect on oxygen release | Why it helps |
|---|---|---|---|
| Carbon dioxide level | High | Increases release | Active tissues produce more carbon dioxide |
| Acidity (pH) | Lower (more acidic) | Increases release | Active tissues produce lactic acid |
| Temperature | Higher | Increases release | Working muscles run hotter |
[!TLDR]
A rightward shift of the dissociation curve from raised CO2, H+ and temperature is th …
The Bohr effect describes how a rise in local CO2 concentration, a rise in H+ concentration (fall in pH), and a rise in temperature -- exactly the conditions generated by actively respiring tissue -- shift the oxyhaemoglobin dissociation curve to the right, lowering haemoglobin's affinity for oxygen at that pO2 and so promoting extra oxygen release exactly where it is most needed. The chloride shift is a separate, unrelated ionic exchange involved in CO2 tr …
Recognise the three listed conditions (CO2, H+/pH, temperature) as the defining triggers of the Bohr …
Confusing the Bohr effect (a rightward shift of the O2-haemoglobin curve, affecting oxygen unloading) with the chloride shift (an ionic exchange balancing bicarb …
- CBSE 2026Set ANNUAL1 markMCQQ.The respiratory pigment in human blood is:(a) Myoglobin(b) Hemoglobin(c) Hemocyanin(d) Chlorophyll
›Reveal solutionSolution
Haemoglobin, packed inside red blood cells, is the respiratory pigment of humans — it binds oxygen in the lungs (where partial pressure of O₂ is high) and releases it in the tissues (where partial pressure of O₂ is low).
Haemoglobin is a conjugated protein made of four polypeptide (globin) chains, each carrying an iron-containing haem group. Each haem group can bind one molecule of O₂, so one haemoglobin molecule can carry up to four O₂ molecules, forming oxyhaemoglobin. About 97% of the oxygen transported in human blood travels bound to haemoglobin this way; only a small fraction dissolves directly in plasma. Haemoglobin also assists in carbon dioxide transport, binding CO₂ as carbaminohaemoglobin.
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- CBSE 2026Set ANNUAL1 markQ.Write True/False: Each molecule of haemoglobin can carry a maximum of two O2 molecules.
›Reveal solutionSolution
This statement is False — a haemoglobin molecule has four heme groups (one on each of its four polypeptide chains), so it can bind and carry a maximum of four oxygen molecules, not two.
Haemoglobin is a globular, iron-containing conjugated protein made of four polypeptide chains (two alpha and two beta chains in adult human Hb), and each chain carries one heme group with a central Fe2+ ion. Each heme group can reversibly bind one molecule of oxygen, so with four heme groups per Hb molecule, one molecule of haemoglobin can carry a maximum of four O2 molecules — not two as stated. This is why haemoglobin sh …
- CBSE 2026Set ANNUAL1 markMCQQ.Which of the following is a respiratory pigment ?(a) Myosin(b) Haemoglobin(c) Chlorophyll(d) Albumin
›Reveal solutionSolution
Haemoglobin is the respiratory pigment, so the answer is (B).
A respiratory pigment is a coloured protein that binds and transports oxygen. In humans this is haemoglobin, a red, iron-containing pigment present in red blood cells. It combines reversibly with oxygen to form oxyhaemoglobin and carries about 97% of the oxygen in the blood.
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- CBSE 2024Set ANNUAL1 markMCQQ.One molecule of haemoglobin can carry a maximum of how many molecules of oxygen ?(a) 2(b) 4(c) 6(d) 8
›Reveal solutionSolution
Haemoglobin is a tetramer with four polypeptide chains, each bearing one haem group, so it can bind a maximum of four O₂ molecules.
Haemoglobin is a respiratory pigment present in the red blood corpuscles, made up of four polypeptide chains (two alpha and two beta chains in adult human haemoglobin), each associated with one haem group containing an iron (Fe²⁺) ion. Each haem group can reversibly bind one molecule of …
- CBSE 2022Set TERM11 markMCQQ.One haemoglobin carries how many molecules of O2?(a) 4(b) 2(c) 6(d) 8
›Reveal solutionSolution
One haemoglobin molecule, with its four heme units, can carry a maximum of 4 O2 molecules.
Haemoglobin is a globular, iron-containing conjugated protein made of four polypeptide (globin) chains (typically two alpha and two beta chains in adult human haemoglobin), each chain carrying one heme group at its core. Each heme group contains one Fe2+ (ferrous) ion, which can reversibly bind one molecule of oxygen (forming oxyhaemoglobin). Because there are four heme groups per haemoglobin molecule, one complete haemoglo …
- CBSE 2021Set ANNUAL1 markMCQQ.O₂ binds with haemoglobin in a reversible manner to form(a) oxyhaemoglobin(b) carbamine haemoglobin(c) both(a) and(b)(d) none of the above
›Reveal solutionSolution
O₂ binds reversibly with haemoglobin to form oxyhaemoglobin, the main way oxygen is carried in blood.
Haemoglobin (Hb), the respiratory pigment present in red blood cells, has a very high affinity for oxygen. In the lungs, where the partial pressure of O₂ (pO₂) is high, oxygen binds reversibly with the iron (Fe²⁺) of the haem part of haemoglobin to form oxyhaemoglobin. This reversible binding allows oxyhaemoglobin to release O₂ again in the tissues, where pO₂ is lower — about 97% of O₂ is transported this way, with only a small fraction dissolved directly in plasma.
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- CBSE 2020Set ANNUAL1 markMCQQ.One haemoglobin carries how many molecules of O2 ?(a) 4(b) 2(c) 6(d) 8
›Reveal solutionSolution
Haemoglobin is a tetrameric protein (2 alpha + 2 beta globin chains), each chain carrying one haem group with an iron atom that can reversibly bind one O2 molecule -- so one haemoglobin molecule carries up to 4 O2 molecules.
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