Consider the following statements about haemoglobin: A ) It carries oxygen in the blood. B ) It is iron containing compound. C ) It provides immunity against certain disease. D ) It imparts red colour to the blood. The correct statements out of these are:

Take the four statements one at a time. Haemoglobin is a protein in red blood cells, and its heme groups contain iron (Fe2+) that binds oxygen in the lungs and releases it in the tissues. So statement 1 is correct, and statement 2 is correct because the iron is what allows it to bind oxygen at all. Statement 4 is also correct: the iron-heme complex gives blood its characteristic red colour, and oxygenated blood looks bright red while deoxygenated blood looks darker.

• Statement 3 is wrong. Immunity comes from antibodies (immunoglobulins), produced by B-lymphocytes, along with other white blood cells. Haemoglobin has no role in immune defence.

So the correct set is 1, 2 and 4, which is option D.

Core concept: structure-function link in respiratory physiology. The iron-heme structure explains oxygen transport, and this connects to Mains topics on nutrition and anaemia, where iron deficiency reduces haemoglobin synthesis and oxygen-carrying capacity.

Trap: candidates sometimes pick option B because they associate blood with immunity, confusing haemoglobin with the white blood cells and antibodies that actually fight infection.