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B1 (Osmosis, Microscopes, Exchanging surfaces, Differentiation of animal…
B1
Osmosis
A partially permeable membrane allows water through, but won't let larger molecules dissolved in water pass through.
Water will move to make the concentrations the same on both sides of the membrane:
When there are lots of water molecules (in a dilute solution) on one side of a partially permeable membrane, but not many on the other side (in a concentrated solution), water will move from the dilute to the concentrated solution.
It is important to remember that water molecules will move through the membrane in both directions, but the net (overall) movement of water will be from the dilute solution to a concentrated solution
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Microscopes
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Required practical
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Draw a low power image of what you see and then change the magnification and refocus using the fine focus adjustment
Exchanging surfaces
Exchange surfaces - surfaces that are adapted to maximize the efficiency of gas and solute (a substance dissolved in a liquid) exchange across them.
Adaptations
Where substances are exchanged through blood in animals, exchange surfaces are densely packed with blood vessels:
These blood vessels replenish the blood supply to maintain a high concentration gradient by bringing in new blood as diffusion starts to even out the concentrations.
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In animals, if a gas is exchanged, the surface is ventilated (through breathing) to maintain a high concentration gradient and increase the rate of exchange
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Examples
The small intestine is adapted for exchanging nutrients between digested food in the small intestine and the blood.
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The gills are adapted for exchanging oxygen that is dissolved in water, with the carbon dioxide in a fish's bloodstream.
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Leaves are adapted for exchanging carbon dioxide and oxygen between the leaves and the surrounding air.
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Plant cells
Cytoplasm, nucleus, ribosome, vacuole, mitochondria, cell membrane, cell wall, chloroplast
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Animal cells
Organelles
Cytoplasm, nucleus, ribosome, mitochondria, cell membrane
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