Part A · Exchange and circulation Exchange and transport in animals mind map

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Exchange surfaces

Cell needs: Deliver nutrients / O₂; remove CO₂ and liver-made urea
Diffusion: Large area, short distance, steep gradient → faster exchange
Size: Larger organisms: lower SA:V and longer transport distances
Cubes: SA = 6l²; V = l³; 1, 2, 3 cm → 6:1, 3:1, 2:1
Alveoli: Large moist surface; two one-cell-thick walls
Gradients: O₂ → blood; CO₂ → air; ventilation and blood flow maintain

Blood and vessels

Plasma: Carries cells, dissolved nutrients, wastes, hormones and heat
Red cells: Haemoglobin carries O₂; biconcave, no nucleus
Defence: White cells: immunity; platelet fragments: clotting
Arteries: Away from heart; thick elastic muscle; pulse is pressure wave
Capillaries: Thin walls, extensive networks; exchange with tissues
Veins: Towards heart; lower pressure, wider lumen; many have valves

Heart and flow

Double circuit: Body → right heart → lungs → left heart → body
Right route: Vena cava → right atrium → right ventricle → pulmonary artery → lungs
Left route: Pulmonary veins → left atrium → left ventricle → aorta → body
Structure: Valves; septum; thicker left ventricle; coronary supply
Cardiac output: Stroke volume × heart rate; 70 × 75 = 5,250 cm³/min
Exercise / training: Immediate demand raises output; training may raise stroke volume

Connections

Exchange surfaces → Blood and vessels: Gas exchange loads oxygen into circulating blood.
Blood and vessels → Heart and flow: The pump drives blood through vessels to tissues.