BLOOD AND IT'S FUNCTION IN THE HUMAN Just over half of the blood volume is made up of a pale yellow fluid called plasma . The rest of the blood is made up of cells (red blood cells and white blood cells) and platelets. Blood has several vital functions: · Transport - oxygen in the red blood cells, absorbed, digested food by the plasma, excretory products by the plasma, hormones by the plasma etc. · Defence - by the white blood cells (a.k.a. leucocytes). · Formation of lymph and tissue fluid. · Homeostasis. Red blood cells Also known as erythrocytes . These contain a pigment, haemoglobin, which gives them their colour. Red blood cells are made in the bone marrow (the liver in a foetus) of many bones. They have a life span of abo...