This month's Challenge Question: Specs & Techs from GlobalSpec:"
Between 10 and 15 atm of pressure would be required to
transport water to the top leaves of California's redwoods, which can reach
heights of 120 meters. How could the water be transported upward such a
distance?
And the answer is:
When two solutions are separated by a membrane, the solvent
in the more dilute solution moves to the more concentrated solution. This
process is well known and it is called osmosis. The movement of solvents produce
pressure in the more concentrated solution. Eventually the process reaches
equilibrium. The pressure at equilibrium (this is the pressure that stops the
osmosis) is called osmotic pressure. Now, let's see how water can be transported
up the tree. The leaves in trees continuously lose water to the air by a
process called transpiration. By losing water the leaf fluid inside becomes
more concentrated. Then the water (less concentrated) surrounding the leaves
(from the trunk, the branches and the stems of the tree) moves inside by
osmosis. Water is pushed up by osmotic pressure. It is not possible to move
water up a big distance by a process called capillarity, because
capillarity is very low pressure process.
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