Which component of blood is responsible for carrying oxygen to the body tissues?

Step 1: Analyze the question The question asks which blood component transports oxygen from the lungs to the body tissues.

Step 2: Explain the concept Blood has four main components, each with its own job:

• Platelets (thrombocytes): help blood clot and stop bleeding.
• White blood cells (leucocytes): defend the body against infections and disease-causing organisms.
• Red blood cells (erythrocytes): carry oxygen. They contain haemoglobin, a red pigment rich in iron that binds oxygen.
• Plasma: the liquid part of blood. It transports dissolved substances such as digested food, hormones, urea and most carbon dioxide (as hydrogencarbonate), but it is not the main oxygen carrier.

Step 3: Work through the solution In the lungs, oxygen diffuses into the blood and combines with haemoglobin in the red blood cells to form oxyhaemoglobin:

Haemoglobin + Oxygen → Oxyhaemoglobin

The blood carries this to the tissues. There, where oxygen concentration is low, oxyhaemoglobin releases its oxygen, which diffuses into the cells for respiration.

Red blood cells are well adapted for this job:

• They are biconcave, which gives a large surface area for gas exchange.
• They have no nucleus in mammals, so there is more room for haemoglobin.
• They are very numerous and flexible enough to squeeze through capillaries.

Step 4: Identify the answer The answer is **C.

Step 5: Exam tip Link each name to its job:

• Red cells → Respiratory gas (oxygen) transport
• White cells → Warriors (defence)
• Platelets → Plugging wounds (clotting)
• Plasma → Pool or liquid transport medium

Keep going, you are doing well!