Pressure in the life of living organisms
As we climb, the air thins, so atmospheric pressure and the amount of oxygen per breath fall: at about 5000 m pressure is nearly half of sea level, and on Everest’s summit (8849 m) about one third. Unprepared people get shortness of breath, dizziness and quick tiredness (altitude sickness), so one climbs high mountains gradually to adapt. People also have blood pressure: in healthy adults about 120/80 mm of mercury. In animals’ bodies the link between area and pressure matters: a mosquito’s proboscis and a bee’s sting have tiny tips so they exert a large pressure and pierce skin; the broad feet of camels, snow hares and lynxes reduce pressure and keep them from sinking into sand or snow. Aquatic animals have internal pressure equal to the outside water pressure, so life exists at depth. Many bony fish have a gas-filled swim bladder: when the fish dives the outside pressure squeezes the bladder, when it rises the bladder expands; by changing the amount of gas the fish can hover at any depth. Sharks have no swim bladder: they stay up with an oily liver and by swimming with their fins.
Test a model: make two plasticine pieces of equal mass, one with a thin point and one with a broad base; set each gently on soft plasticine or dough and compare which sinks deeper. Safety: use nothing sharp, keep plasticine and dough out of the mouth and wash hands afterwards.