Blood is important in multicellular organisms because it flows around the body, transporting substances to and from cells.
Blood transports materials and distributes heat around the body. It also helps to protect against disease. Blood contains a liquid called plasma. Suspended in the plasma are cells and cell fragments, such as:
This table explains the functions of various blood components.
|Plasma||Transporting carbon dioxide, digested food molecules, urea and hormones; distributing heat|
|Red blood cells||Transporting oxygen|
|White blood cells||Ingesting pathogens and producing antibodies|
|Platelets||Involved in blood clotting|
Plasma is made primarily of water. Many of the molecules the body needs to transport, such as urea, carbon dioxide and glucose, are soluble in water. This means that a large number of substances can be transported around the body in plasma at any one time. This ability to transport important substances around makes plasma well adapted to meet its function.
Red blood cells transport the oxygen required for aerobic respiration in body cells.
Red blood cells have adaptations that enable them to carry a maximum amount of oxygen:
Haemoglobin can combine reversibly with oxygen. This is important - it means that it can combine with oxygen as blood passes through the lungs, and release the oxygen when it reaches the cells.
You may be given some prepared slides of blood to examine with the microscope.
Many types of blood cell are 10 μm in diameter or less. You will need to use a high magnification to examine them.
The slides will have been stained to show the cells, and cell features. The micrograph shows many red blood cells and three white blood cells.