a. Platelets- Platelets are cell fragments formed in the bone marrow. They are also called thrombocytes. Platelets carry blood coagulation factors on their surfaces, hence have a major role in initiating blood clotting. They are also involved in maintaining homeostasis.

b. Haemoglobin- Haemoglobin is a special protein found in the red blood cells that imparts red colour to the blood. It picks up oxygen from lungs to form oxyhaemoglobin and delivers it to the tissues. It maintains blood pH to tolerable limits.