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Exchange
Diffusion, Osmosis & Active Transport
· Diffusion is the movement of substances
through a membrane from a high to low
concentration.
· Osmosis is the movement of water through a
partially permeable membrane from a high to
low concentration
· Active transport is the movement of
substances in & out a cell from a low to high
concentration. It uses energy.…read more

Slide 3

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Exchange
Diffusion/ Transpiration in Plants
· The underneath of the leaf is an exchange surface for
gasses.
· It's covered in stomata holes, which are controlled by
the guard cells.
· Water, oxygen, & carbon-dioxide diffuse through the
stomata.
· The leaf is adapted to have a large surface area for
exchange by the flattened shape & air spaces.
· The diffusion of water out of the leaf is called
transpiration. This is quickest in dry, hot, windy
conditions (plants don't like transpiring, they need
water).…read more

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Exchange
How guard cells work
· They become turgid and swollen when the
plant has lots of water in it.
· This means they open the stomata, which
assists gas exchange and transpiration.
· So when the guard cells are flaccid and thin,
they close the stomata, thus preventing any
further water loss (as the plant is already
lacking water).…read more

Slide 5

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Body Functions
Breathing in & out
· Breathing in: · Breathing out:
· Intercostal muscles and · Intercostal muscles and
diaphragm contract. diaphragm relax.
· Thorax volume · Thorax volume
increases. decreases.
· Air is drawn in. · Air is forced out.…read more

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Body Functions
The Alveoli in the lungs
· The lungs function is to get oxygen into the
blood, and remove waste carbon-dioxide.
· They do the gas exchange in the alveoli.
· The alveoli have a large surface area for
diffusion, a moist lining for dissolving gasses,
thin walls for diffusion, and a copious blood
supply to maintain a steep concentration
gradient.…read more

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