Q.Name the respiratory pigment present in human red blood cells that binds and transports oxygen.

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.

The distractors are other pigments found elsewhere: myoglobin is the oxygen-storing pigment of muscle tissue (not the main transport pigment in blood); haemocyanin is a copper-based respiratory pigment used by many molluscs and arthropods, not humans; chlorophyll is a plant photosynthetic pigment, unrelated to respiration.

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 shows cooperative binding of O2 (the sigmoidal oxygen-dissociation curve), where binding of one O2 molecule makes it easier for the next ones to bind.

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.

Myosin is a muscle protein, chlorophyll is a plant photosynthetic pigment, and albumin is a plasma protein — none of these is a respiratory pigment. So the answer is haemoglobin.

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 oxygen. Since there are four haem groups per haemoglobin molecule, one molecule of haemoglobin can carry a maximum of four molecules of O₂ (forming oxyhaemoglobin).

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 haemoglobin molecule can bind and transport up to 4 molecules of O2 -- this cooperative binding across the four subunits is also what gives haemoglobin's oxygen-dissociation curve its characteristic sigmoid shape.

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.

Carbamino-haemoglobin (option b) is instead formed when CO₂ (not O₂) binds reversibly to the amino groups of the globin (protein) part of haemoglobin — this is one of the ways carbon dioxide, not oxygen, is transported from tissues back to the lungs. Since the question specifically concerns O₂ binding, options (c) and (d) are incorrect.

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.

Oxygen transport in blood relies on haemoglobin inside red blood cells. Each of the four globin subunits of a haemoglobin molecule holds a haem prosthetic group, and each haem's central Fe2+ ion binds one molecule of O2 -- giving the classic cooperative, sigmoidal oxygen-dissociation curve as the four sites bind O2 progressively.