Blood
Blood is important in multicellular organisms because it flows around the body, transporting substances to and from cells.
The composition of blood
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:
- red blood cells
- white blood cells
- cell fragments called platelets
This table explains the functions of various blood components.
| Component | Function(s) |
| 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 |
| Component | Plasma |
|---|---|
| Function(s) | Transporting carbon dioxide, digested food molecules, urea and hormones; distributing heat |
| Component | Red blood cells |
|---|---|
| Function(s) | Transporting oxygen |
| Component | White blood cells |
|---|---|
| Function(s) | Ingesting pathogens and producing antibodies |
| Component | Platelets |
|---|---|
| Function(s) | Involved in blood clotting |
Transporting substances in plasma
Plasma is made primarily of water. Many of the molecules the body needs to transport, such as A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine., 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.
Adaptations of red blood cells for oxygen transport
Red blood cells transport the oxygen required for Respiration that requires oxygen. in body cells.
They must be able to absorb Gaseous element making up about 20% of the air, which is needed by living organisms for respiration. in the lungs, pass through narrow blood Tiny blood vessels with walls one-cell thick where exchange of materials occurs., and release this oxygen to To engage in respiration, the energy-producing process inside living cells. cells.
Red blood cells have adaptations that enable them to carry a maximum amount of oxygen:
- They contain the Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.The red protein found in red blood cells that transports oxygen round the body., which gives them their red colour, at the lungs.
\( \text{haemoglobin} + \text{oxygen} \xrightarrow {at~the~lungs} \text{oxyhaemoglobin}\)
\( \text{haemoglobin} + \text{oxygen} \xleftarrow {at~the~cells} \text{oxyhaemoglobin}\)
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.
- They have no The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei. - they lose it during their development - so they can pack in more haemoglobin.
- They are small and flexible so that they can fit through narrow blood capillaries.
- They have a biconcave shape - they are the shape of a disc that is curved inwards on both sides - to maximise their surface area for oxygen absorption.
- They are thin, so there is only a short distance for the oxygen to diffuse to reach the centre of the cell.
Looking at blood 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.
More guides on this topic
- How does the nervous system help us respond? - OCR 21st Century
- Why do we need to maintain a constant internal environment?
- What role do hormones play in human reproduction? - OCR 21st Century
- What can happen when organs & control systems stop working?
- Sample exam questions - the human body - staying alive
