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B3 1 Summary
Exchange of materials
Chapter review
AQA Science © Nelson Thornes Ltd 2006
1
B3 1 Summary
How do substances move in and
out of cells?
• Diffusion – passive movement of substances
along a concentration gradient.
• Osmosis – movement of water along a
concentration gradient through a partially
permeable membrane.
• Active transport – movement of substances
against a concentration gradient, or across a
partially permeable membrane, using energy
produced by respiration.
AQA Science © Nelson Thornes Ltd 2006
2
B3 1 Summary
How are the lungs adapted for
effective gas exchange?
• Breathing movements –
good concentration gradient.
• Alveoli – massive surface
area for diffusion.
• Moist surfaces so gases
dissolve for efficient diffusion.
• Rich blood supply – so
concentration gradient
maintained.
• Short distance between
alveoli and blood.
AQA Science © Nelson Thornes Ltd 2006
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B3 1 Summary
How is your gut adapted for the
absorption of your food?
• Large food molecules broken down
into small food molecules
(digestion).
• Villi – large surface area for
diffusion.
• Rich blood supply – maintains
concentration gradient for diffusion.
• Short distances for diffusion.
• Moist surfaces.
• Active transport of substances.
AQA Science © Nelson Thornes Ltd 2006
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B3 1 Summary
What adaptations are needed for
exchange of gas and solutes in
any organism?
• A large surface area to give plenty of
opportunity for substances to diffuse.
• A way of removing the substances
exchanged (e.g. a rich blood supply) to
maintain a steep concentration gradient and
carry them to where they are needed.
• Moist surfaces for substances to dissolve.
• A short distance between the two areas –
this makes diffusion as effective as possible.
AQA Science © Nelson Thornes Ltd 2006
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B3 1 Summary
How are plants adapted for
exchange of substances?
• Leaves: flat and thin for large
surface area and short diffusion
distances; internal air spaces;
stomata to let air in and out.
• Roots: many tiny roots and root
hairs for large surface area;
short diffusion distances; active
transport to work against
concentration gradients.
Photo: John Kaprielian
AQA Science © Nelson Thornes Ltd 2006
6
B3 1 Summary
What is transpiration and what
factors affect it?
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Temperature.
Light levels.
Air movements.
Carbon dioxide
levels.
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