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· Osmosis is the movement of water molecules across a partially permeable
membrane from a region of high water concentration to a region of low
water concentration
· A partially permeable membrane is just a membrane with a number of tiny
holes in it so that small molecules such as water can pass through
· During osmosis, water tries to `balance out' the concentration of a solution
which contains less water with the area with lots of water, meaning that it
makes the solution more dilute…read more

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· Tissue fluid surrounds the cells in the body
· It's basically water with oxygen, glucose and other substances dissolved in it
· Tissue fluid is squeezed out of the blood capillaries to supply the cells with
everything they need
· The tissue fluid usually has a different concentration to the fluid inside the
cell. This means that the when the cell contains more water than the
surrounding fluid, the water will travel out of the cell and into the tissue fluid
by osmosis, and vice versa.…read more

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An Osmosis Experiment
· Cut a potato into identical cylinder shapes and measure them.
· Collect several beakers, each with different concentrations of sugar solution.
One should be pure water, one should be a highly concentrated sugar
solution, and the remaining beakers should be in between.
· Leave the potatoes in the beakers for 30 minutes. When the time is up, re-
measure the potato cylinders. Potatoes which have gotten longer have drawn
in water by osmosis, whereas potatoes shorter than before have given out
water by osmosis.…read more

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Gas and Solute Exchange
· For life processes to occur in an animal or plant, gases or other dissolved
substances need to get inside the cells.
· As well as this, waste substances such as CO2 need to be removed from the
· This is where diffusion, osmosis and active transport come in.
· Diffusion is the movement of particles from an area of high concentration to
an area of low concentration. An example of this is gases diffusing through
each other, much like the way perfume diffuses through the air.…read more

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Exchange Surfaces
· Gases must diffuse through some sort of exchange surface to get to the place
they need to be. This exchange surface must allow enough of the gas to get
through, and so are specially adapted to maximise effectiveness:
· They are thin- substances only have a short distance to diffuse
· Large surface areas- more of the gas can diffuse at one time
· Exchange surfaces in humans have lots of blood vessels which means that
substances can get into and out of the blood quickly
· Exchange surfaces in animals are often ventilated, too (air moves in and out)…read more

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