The Standard two class, of Rangiwahia School, asks :-

Why do we have blood?

David Parry, a biophysicist at Massey University, responded.

Probably the most important role of the blood is one of transport. The blood distributes nutrients, water, vitamins, hormones, chemicals, cells and gases to the tissues and organs. If for some reason through sickness or injury the blood is not able to perform this function, we would not be able to survive.

Blood is comprised of blood cells that are produced in the bone marrow in humans and other vertebrates. The blood cells are suspended in a straw coloured liquid called plasma that transports them around the body. The three main cells that can be found in the blood are red cells (erythrocytes), white cells (leucocytes) and platelets.

The major role of red cells is gas transport. They are packed with a complex protein molecule called haemoglobin which picks up oxygen in the lungs and deposits it in body tis- sues. They then are able to pick up carbon dioxide from the tissues and transport this back to the lungs where it is expelled when we breath out.

White cells have two major roles, both to do with protecting the body. Some eat and de- stroy (phagocytose) bacteria and viruses that we encounter every day. While many of these bugs are harmless others would cause disease if they were allowed to invade our body and mul- tiply. Some white cells called lymphocytes provide us with immunity to bacteria and viruses. Lymphocytes produce proteins called immunoglobulins that together with phagocytes provide an even more effective defense mechanism against invaders.

Platelets are the smallest cells of the blood. Their job is to prevent blood loss. When we cut or injure ourselves platelets clot together at the wound to stop the bleeding.