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1.1 Active Transport
Osmosis and diffusion involve moment of substances from a higher
concentration to a lower concentration.
- A cell may need to take up a substance against the concentration gradient.
This involves energy and is called `ACTIVE TRANSPORT'.
- Active Transport is the only one of the three methods that requires energy.
It is only worth the cell using this energy if the substance involved is really
needed.
KEY WORDS:
Concentration,
Gradient,
Active Transport,
Energy.…read more

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1.2 Exchange of Gases in the Lungs
The lungs exchange OXYGEN (aerobic respiration) and CARBON DIOXIDE
(waste product of aerobic respiration) with the atmosphere. They have a
very large surface area provided by millions of ALVEOLI (air sacs). The
surfaces of the lungs are MOIST and THIN so diffusion takes place quickly.
Oxygen diffuses into the many CAPILLARIES surrounding the alveoli and
carbon dioxide diffuses back out into the lungs.
KEY WORDS:
Diffusion, Alveoli, Moist,
Surface Area.…read more

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1.3 Exchange in the Gut
Food we eat is digested in the gut into SMALL, SOLUBLE molecules. In the
small intestine these are absorbed by the blood, in which there is a rich
supply. Finger-like projections into the small intestine, VILLI, greatly
increase the surface area of absorption to take place.
Food is absorbed, where there is a low concentration of that molecule in the
blood. Food is absorbed by active transport where movement is against the
concentration gradient. ­ DIFFUSION & ACTIVE TRANSPORT.
KEY WORDS:
Villi (villus: singular).…read more

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1.4 Exchange of Materials in other
Organisms
All living organisms need to exchange gases. They need OXYGEN for
RESPIRATION and to remove CARBON DIOXIDE.
These organisms have a number of features in common:
- They have a large surface area.
- They are moist.
- The gases are transported away quickly to maintain a high gradient.
- The membranes which the gases diffuse across are thin.
KEY WORDS:
Surface Area, Concentration Gradient, Membrane.…read more

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1.5 Exchange in Plants
Gases diffuse in and out of leaves through tiny holes called `STOMATA'.
- Oxygen is needed for respiration and is a waste product of
PHOTOSYNTHESIS.
- Carbon Dioxide is needed for photosynthesis and is a waste product of
RESPIRATION.
The movement of these gases depends upon which process is taking place the
most quickly.
Leaves are flat and very thin so the gases do not need to diffuse very far. There
are also internal air spaces.
Water and mineral ions are taken up by roots. Roots have thousands of tiny
projections called root hairs to increase the surface area ­ water evaporates
from the leaves, and this can be a problem.
KEY WORDS:
Stomata, Photosynthesis, Respiration, Diffusion.…read more

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