Osmosis is the diffusion of water particles through a selectively permeable membrane from areas of high water concentration (low solute) to areas of low water concentration (high solute).
From revision notes:
(Water molecules always travel through a cell membrane; this is the selectively permeable membrane. This selectively permeable membrane only allows water through, and does not allow though any solutes.
Water molecules are much smaller than the dissolved particles (solutes) and so are able to pass through the pores in the membrane.
This means that water will still move, either; from PURE WATER (DISTILLED WATER) into a DILUTE SOLUTIONS, or; from a DILUTE SOLUTION into a more CONCENTRATED SOLUTION. The more concentrated a solution is, the less water there is.
We can use this theory of osmosis to explain the movement of water into the root hairs cells of plants. The water in the soil is a dilute solution; the cytoplasm in the root hair is a ...view middle of the document...
If the opposite occurred and there was more water outside the cells there would be a net gain of water and the cells would burst. Therefore it is vital that the composition of out blood and other body fluids is regulated. This is an example of homeostasis or regulation of our internal environment.
Diffusion is affected by the following factors:
* Concentration â€“ the greater the difference in concentration between two substances the more rapidly diffusion takes place.
* Temperature â€“ the higher the temperature, the greater the speed of molecular motion.
* Pressure â€“ the higher the pressure on particles, the greater the speed of diffusion from a region of high-pressure to a region of low pressure.
If a cell were completely permeable it would die, as no water (or substance) would be able to move through its membrane.
Osmosis in plant cells
Plant cells have a strong rigid cell wall on the outside of the cell membrane. This stops the cell bursting when it absorbs water by osmosis. The increase in pressure makes the cell rigid. This is useful, as plants do not have a skeleton. Instead the pressure of water in their cells can support the leaves and shoots. If plant cells lose too much water by osmosis they become less rigid and eventually the cell membrane shrinks away from the cell wall.
Water entering the cell by osmosis inflates the cell and makes it rigid
Loss of water makes the cell limp and shrinks the cell membrane away from the cell wall.
What question are we going to be investigating?
We will be investigating the effect of the concentration of sucrose on osmosis.
I predict that the higher the concentration of sucrose in the visking tube, the more osmosis will take place. This is because there are less water molecules inside the tube than there is out and therefore the water molecule will move from the area of high water concentration (outside) to the area of low water concentration (inside). Weâ€™d be able to test this because as the water molecules enter the tubing, the weight will increase, the higher the increase in weight, the more osmosis has taken place.
For example if there was a visking tube with 30% sucrose in it, and one with 70%, the one with 70% sucrose in it will have a higher weight gain as more water will enter the tube.