Osmosis is defined as the movement of water molecules from a region of higher water potential (dilute solution or lower concentration of the solute) to a region of lower water potential (higher concentration of the solute or concentration of the solution) through a semi-permeable/selectively permeable membrane.
Osmosis is defined as the movement of water molecules from a dilute solution to a concentrated solution through a semi-permeable / selectively permeable membraneA semipermeable membrane is a layer that only certain molecules can pass through. Smaller molecules like water can pass but not the bigger molecules like solutes. It allows cells to keep... More.
If a concentrated solution is separated from the dilute solution by a semi-permeable membrane, water diffuses across the membrane from the dilute solution by the process of osmosis.
The weaker solution is said to be hypotonicHypotonic solution refers to a solution containing a lower solute concentration in comparison to the solute concentration in another solution, across a semipermeable membrane. Such a solution has a decreased solute... More and the stronger solution is described as hypertonicA hypertonic solution refers to a solution containing a higher solute concentration in comparison to the solute concentration in another solution, across a semipermeable membrane. More, when both solutions have the same concentration, they are described as isotonicAn isotonic solution is when two solutions, separated by a semipermeable membrane, have equal concentrations of solutes and water. More.
Osmosis provides the primary means by which water is transported into and out of cells.
Experiment – Osmosis in a Non–living System:
1. Tie a piece of cellophane paper over the mouth of a thistle funnel using a rubber band.
2. Fill the thistle funnel with a strong sugar solution. Mark the level of the sugar solution.
3. Lower the thistle funnel into a beaker of water such that the levels of the sugar solution in the thistle funnel and in the beaker are the same.
4. Set up a control experiment; add water into the thistle funnel instead of sugar solution.
5. Allow the experiment to stand for some hours.
The level of water in the beaker drops while the level of the sugar solution rises
Water molecules move from a region of higher concentration (the beaker) through the selectively permeable membrane (cellophane paper) into the thistle funnel by osmosis.
Experiment – Osmometer with Living Material:
Activity – osmosis in living tissue:
1. Remove the skin of a potato tuber. Cut it into two equal halves with a blade.
2. Make a square or a circular shaped cavity in the centre of the slice.
3. Place the slices of yam in a trough containing water.
4. Add freshly prepared 20% sugar solution into the cavity of the tubers and water into the second.
5. Mark the level of water and sugar in the trough and yam cavity.
6. Allow the set-up to stand for some hours.
7. Notice the sugar solution in the osmometer towards the end of the experiment.
The level of the sugar solution has risen resulting in a decrease in the level of the water trough.
The yam tissue is acting as a semi-permeable membrane. Water molecules moved through the yam tissue into the cavity of the yam by osmosis as a result of the difference in the concentration. This shows that osmosis has taken place.
Differences between Diffusion & Osmosis:
|1.||Diffusion occurs in gases and liquids||Osmosis occurs only in liquids mediums|
|2.||Semi permeable membrane not required||Semi permeable membrane is required|
|3.||Occurs in living and non-living organisms||Occurs naturally in living organisms|
(i) Osmotic Pressure: The pressure that a solution can potentially exert is called Osmotic pressure.
(ii) Water Potential: The water potential of a solution is a measure of whether it is likely to gain or lose water molecules from another solution.
(iii) Semi-permeable membrane: A layer that only certain molecules can pass through.
(iv) Hypotonic – weaker solution, Hypertonic – stronger solution, Isotonic – same concentration.
(v) Osmosis provides the primary means by which water is transported into and out of cells.