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Slide 2

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Exchange between Organisms and Environment
Organisms must transfer materials b/w themselves & their environment. Why?
· To rapidly distribute the absorbed materials to the cells.
For survival
· For the removal of waste products from the body.
Substances that are interchanged among organisms & their environment
· Respiratory gases (Oxygen and Carbon Dioxide)
· Nutrients (fatty acids, glucose, amino acids, vitamins and minerals)
· Excretory products like urea and CO2
· Heat…read more

Slide 3

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Exchange of materials requires a transport system
There are two types of transport mechanisms
· Passively (no energy required): diffusion and osmosis
· Actively (energy required): active transport
The child swings In order to swing,
by himself. No an external push
external energy is or energy is
used. required.
Passive Active…read more

Slide 4

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Surface area to volume ratio
Surface area of the organism must be large compared with its volume
If the organism is small in size, the surface area to volume ratio will be
large and hence they perform effective exchange.
As the size increases, the surface to volume ratio decreases.…read more

Slide 5

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As organisms become larger, their volume increase at a
faster rate than their surface area.
But this is of course a problem because the exchange of
materials will not be inefficient. It would take too long for
it to reach the middle of the organism if diffusion alone is
used as the method of transport.
Then, how do large organisms overcome this problem?
By evolving certain adaptations
· Flattened shape so that the cells are close to surface (flatworm)
· Specialized exchange surface with large area to increase surface
area to volume ratio (lungs in mammals, gills in fish)…read more

Slide 6

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Features of a specialized exchange surface
What are the characteristics of an effective exchange surface?
· a large surface area to volume ratio to increase the rate of exchange
· very thin so as to have a short diffusion distance
· partially permeable membrane to allow exchange of selected molecules
· movement of the environmental medium like air to have a gradient
· movement of the internal medium like blood (for diffusion gradient)
Fick's Law of diffusion…read more

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