blood

• blood is mostly made up of plasma, red blood cells (erythrocytes) , white blood cells (leukocytes) and platelets (thrombocytes)
• red blood cells contain haemoglobin, which carries oxygen
• the shape of red blood cells is a biconcave disc, giving them a large surface area
• in the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin. in body tissues, the reverse happens
• white blood cells defend against infection
• some white blood cells can change shape to engulf unwelcome microorganisms in a process called phagocytosis
• some white blood cells produce antibodies to fight microorganisms
• red blood cells do not have a nucleus to allow more room for oxygen
• as opposed to red blood cells, white blood cells have a nucleus
• platelets help the blood clot
• platelets allow clots to form in wounds, stopping the body from fully bleeding out
• lack of platelets can cause excessive bleeding and bruising (a condition known as haemophilia)
• plasma is the liquid that carries everything in blood