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Slide 1

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Unit 3 biology…read more

Slide 2

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Exchange of materials…read more

Slide 3

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Active Transport
Active transport
Osmosis and diffusion
involves moving
involve the movement of BUT
substances against
substances from a HIGH
the concentration
to LOW concentration.
gradient, therefore
This is passive ­ does not
using energy.
require energy.…read more

Slide 4

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Exchange of gases in the lungs
The lungs exchange oxygen and
carbon dioxide with the
atmosphere. They have a very large
surface area provided by millions of
air sacs called alveoli. The lungs are
moist and thin so that diffusion
takes place quickly.
Oxygen diffuses into the many
capillaries surrounding the alveoli
and carbon dioxide diffuses back
out into the lungs.…read more

Slide 5

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Exchange in the gut
The food we eat is digested in the gut into small, soluble molecules to be absorbed by
the blood in the small intestine. For this to take place efficiently a large surface area is
needed. In the small intestine small `finger-like projections' called villi increase the
surface area for absorption to take place.
Food is absorbed by diffusion when there is a lower
concentration of that molecule in the blood. However it is
absorbed by active transport when there is a higher
concentration of that molecule in the blood, therefore
moving against the concentration gradient. This is to make
sure that all food is absorbed and none is wasted.…read more

Slide 6

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Exchange of materials in other
All living organisms need to exchange gases as they all need oxygen for respiration.
These organisms all have these features:
· Large surface area
· Moist
· Gases are transported quickly to maintain a high concentration gradient
· Membranes are thin
Fish exchange oxygen through their gills, frogs through their skin and insects through
holes in their sides.…read more

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