ZIMSEC O-Level Biology (4025)

Respiration, Breathing and Circulation: notes

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Aerobic respiration: glucose + oxygen gives carbon dioxide + water + energy.
Anaerobic respiration: in muscles it gives lactic acid; in yeast it gives ethanol and carbon dioxide.
Breathing in: ribs move up and out, the diaphragm flattens, and lung volume rises.
Alveoli: thin walls, rich blood supply and a moist surface give fast gas exchange.
Smoking: tar causes cancer, carbon monoxide reduces oxygen carried, nicotine is addictive.
Heart: four chambers; the left side pumps oxygenated blood to the body.
Vessels: arteries have thick walls and high pressure; veins have valves; capillaries have walls one cell thick.
Blood: red cells carry oxygen, white cells fight disease, platelets help clotting, plasma carries dissolved substances.