July 18, 2021
Why is blood so important?
- An adult has about 5 litres of blood. Although blood is liquid, it is also an organ containing many different types of specialised cells that carry out particular functions in your body
- These have all differentiated from blood stem cells and become specialised
The composition of blood
You will most definitely be asked about this in I/GSCE Biology
- Blood is made up of four main components: plasma, red blood cells, white blood cells and platelets
- Plasma is a yellow liquid. It transports dissolved substances such as carbon dioxide, food substances and hormones
- Red blood cells contain the red pigment haemoglobin. Haemoglobin can combine reversibly with oxygen to form oxyhaemoglobin:
haemoglobin + oxygen = oxyhaemoglobin
- When blood passes through the lungs the haemoglobin combines with oxygen
- Oxyhaemoglobin is transported in red blood cells around the body to the tissues, where the oxygen is then released so that the tissue cells have oxygen for aerobic respiration
- A red blood cell has the shape of a biconcave disc - it has a dimle on both sides. This adaptation gives a large surface area to volume ratio for oxygen to diffuse into and out of the cell
- A red blood cell also has no nucleus and this makes room for as much haemoglobin as possible
- White blod cells are part of the body's defences against disease
- Some white blood cells make antibodies - these are proteins that bind to the microorganisms that cause disease and destroy them
- Other white blood cells surround and destroy any foreign cells that get into the body
- All the white blood cells have a nucleus
- Platelets are tiny fragments of cells (and so do not have nuclei)
- They are important in making blood clot if you cut or damage your blood vessels
- The clot dries out and forms a scap which also stops microorganisms getting into the body
Drafted by Catrina (Biology)