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IGCSE: Biology - Circulation
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IGCSE: Biology - Circulation Triple award content course summary
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Circulation:Red blood cells: transport oxygen from lungs to cells. Adaptations → Biconcave shape (Large SA for
absorbing and releasing oxygen.) No nucleus which means more space. Contain hemoglobin which bind
to oxygen to form oxyhaemoglobin.
White blood cells:
- Phagocytes detect things that are foreign in the body, such as pathogens. These then engulf the
pathogens and digest them. They are non specific - will destroy anything foreign.
- Lymphocytes destroy specific pathogens, by recognising antigens on the surface of a pathogen.
They then produce antibodies specific to the pathogens antigens, which attach to the pathogen
so other white blood cells can detect them and destroy them.
There are also memory cells, which remain in the body and remember a specific antigen, meaning they
can produce antibodies faster, and in greater numbers if reinfected by the same pathogen. This is how
you become immune to a disease if you have already had it.
Vaccinations contain a dead or inactive pathogen, which have antigens. This is in a small amount - not
enough to become seriously ill. Most people have Measles and Polio vaccines.
Plasma: Yellow liquid. Carries the substances in your blood (White blood cells, red blood cells, platelets)
Transports: Carbon dioxide, Glucose, amino acids, Urea, Hormones. Urea is a waste product which is
transported from the liver where it is produced to the kidneys where it is removed in urine. Hormones
are chemical messengers, produced by a gland which travel in the blood to target organs / cells.
Platelets: Small fragments of cells. These help the blood to clot. When a blood vessel is damaged, these
group together (held by fibrin - a protein) to block the damaged area. The clot reduces blood loss, and
prevents microorganisms entering .
Arteries Carry blood away from the heart.Arteries have thick, muscular walls and a very narrow lumen. This is
because they need to transport blood at high pressures around the body.
Veins Carry blood back to heart.Veins have thin walls and a wider lumen, as the blood is at lower pressures. Veins
also have valves, to prevent the backflow of blood.
Capillaries Where exchange of materials between blood / tissues occurs. Capillaries are much smaller - they carry blood
close to every cell. Walls are 1 cell thick and permeable so substances can diffuse in and out.
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