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Summary Transport in Animals A Level Biology
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Revision notes for Biology Transport in Animals OCR Biology A As/A Level
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TRANSPORT IN ANIMALSOPEN CLOSED
Explain the need for transport systems in multicellular Very few vessels to contain transport medium Blood enclosed in blood vessels
animals Pumped stsraight from heart to body cavity Doesn't come directly into contact with body cells
In body cavity (haemocoel) medium is under low pressure Heart pumps blood around body under pressure
• Low SA:V as we get bigger, diffusion not enough. Comes into direct contact with the tissues and the cells Substances enter & leave blood by diffusion through vessels
Medium returns to heart through open-ended vessel Blood flow adjusted by widening/narrowing vessels
• Increased metabolism – more O2 and nutrients required. Invertibrate animals; most insects All vertibrates and starfish.
• To remove waste e.g. CO2.
SINGLE DOUBLE
Fish; annelid worms Birds and most mammals
Blood flows through heart once for each circulation Blood flows twice through heart for each complete circulation
Blood flows through two sets of capillaries Blood pumped from heart to lungs = get O2 and unload CO2
Blood returns to heart slowly due to very narrow vessels Blood flowws through heart and is pumped around the body
Low pressure = low efficiency of exchange so activity in these High activity of these animals maintained by high pressure
animals are low except for fishes as there are 3 vessels
Exception: fish = countercurrent gas exchange; don't maintain
their body temp.
Describe how tissue fluid is formed from plasma
• At arterial end of capillary, blood is under high pressure
(hydrostatic pressure).
• This tends to push out blood fluid from the capillaries.
• Can leave through tiny gaps in capillary wall
• Contains plasma with dissolved nutrients and O2.
ARTERIES CAPILLARIES VEINS
Carry blood at high pressure Once cell thick - short diffusion diffusion Carry blood at low pressure
Carry oxygenated blood (except pulm. artery) Where most exchange occurs Carry deocygenated blood (except pulm. vein)
Small lumen = maintain pressure Lumen same size as RBCs Large lumen = ease blood flow
Thick wall with collagen - withstand pressure Many of them - large SA for diffusion Thin walls - no pressure to maintain
Elastic tissue- allow wall to stretch and recoil (pulse) Valves - prevent backflow of blood
Smooth muscle - constrict and contract Carry blood to heart
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