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EXCHANGE AND TRANSPORT IN ANIMALS
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exchange surfaces & transport system in multicellular organisms: surface area : volume ratio
Single-celled organisms: large surface area compared to volume
gases / dissolved substances can diffuse directly in/out cell across cell membrane – enough substances can be exchanged
across membrane to supply the cell’s volume
Multicellular organisms: smaller surface area compared to volume
difficult to exchange enough substances to supply its entire volume across only its outside surface
Need: exchange surface for efficient diffusion
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rate of diffusion
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blood
Red blood cells / erythrocytes: carry oxygen from lungs to all cells in body
Biconcave disc shape – larger surface area for absorbing oxygen
No nucleus – more room for oxygen
Haemoglobin: red pigment – contains iron
In lungs: binds to oxygen – become oxyhemoglobin
In body tissue: oxyhemoglobin splits to release oxygen into cells
White blood cells defend against infection
Phagocytes: change shape to engulf microorganism – phagocytosis
Lymphocytes: produce antibodies against microorganisms
Some produce antitoxins to neutralise toxins produced by microorganisms
Plasma: Pale yellow liquid that carries everything – 55%
Platelets: helps blood to clot – stops blood pouring out & microorganisms getting in
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heart & circulatory system
Double circulatory system: heart pumps blood in 2 circuits
Fish – single circulatory system: deoxygenated blood from body picks up oxygen at gills and goes to heart
Blood comes into atriums: vena cava & pulmonary veins
Atria contract: blood to ventricles
Ventricles contract: blood leaves through pulmonary artery & aorta
Right: deoxygenated
Vena cava: deoxygenated blood from body → right atrium
Pulmonary artery: deoxygenated blood from right ventricle → lungs
Left: oxygenated
Pulmonary vein: oxygenated blood from lungs → left atrium
Aorta: oxygenated blood from left ventricle → whole body
Valves prevent back-flow
Tricuspid/bicuspid valve: prevent back-flow to atria – when ventricles contract
Semilunar valves: prevent back-flow to ventricles when they relax
Relative thickness of chamber walls
Left ventricle has thicker walls – needs more muscle to pump blood round whole body at high pressure
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