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biology 0610printed 115 · PDF 115
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printed 115 · PDF 115
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Blood cells:
The blood contains red blood cells, white blood cells and platelets amongst many
other substances.
Plasma is the liquid which contains soluble nutrients, the blood cells and urea etc
Red blood cells contain haemoglobin which binds to oxygen to become
oxyhaemoglobin. They don’t have a nucleus to enable more packing for haemoglobin.
Haemoglobin releases the bonded oxygen to the cells in need. They are disc shaped
and biconcave
White blood cells are immunity related cells. They fight off pathogens. White blood
cells are subdivided; one white blood cell type is lymphocytes. Lymphocytes produce
antibodies. Antibodies are specific to specific antigens. Antibodies allow for fighting
against the particular pathogen, often holding it in place for phagocytes to come and
consume them.
Phagocytosis and platelets:
Phagocytes recognise and attach to the particular pathogen, engulfing it. The
pathogen is trapped inside and the phagocyte releases enzymes to enable
breakdown of the pathogen, killing it. This process is called phagocytosis
Platelets are small fragments involved in blood clotting. Blood clotting occurs when a
blood vessel is broken or damaged. Platelets stick to the broken blood vessel wall.
This causes a protein known as fibrinogen to convert into fibrin which forms a mesh
fibre around the breakage. More platelets come and attach themselves, trapping other
cells around the site in the process. This creates a scab and prevents further
bleeding, allowing the blood vessel to heal.