Monday, February 28, 2011

3.2 MOVEMENT OF SUBSTANCE ACROSS THE PLASMA MEMBRANE IN EVERYDAY LIFE

THE EFFECTS OF HYPOTONIC, HYPERTONIC AND ISOTONIC SOLUTIONS ON ANIMAL AND PLANT CELLS

1. Hypertonic solution is the solution with a higher solute concentration ('hyper': more).
2. Hypotonic solution is the solution with a lower solute concentration ('hypo' : less).
3. Isotonic solution is the solution in which the concentration of solutes are equal ('iso' : equal).


A. PLANT CELLS IN AN ISOTONIC SOLUTION
1. If a plant cell is immersed in an isotonic solution such as 5% sucrose solution, there is no net movement of water across the plasma membrane.
2. Water flows across the membrane at the same rate in both directions.
3. The cell's volume and shape remain constant.





Effect of Isotonic Solution on a Plant Cell






B. PLANT CELLS IN A HYPOTONIC SOLUTION
1. When a plant cell is immersed in a hypotonic solution such as water, water molecules diffuse into the cell by osmosis.
2. The vacuole gain water, expands and exerts pressure outwards on the cell wall.
3. This pressure is called turgor pressure which cause the plant cell to become turgid.
4. The turgidity of the cells give the plant mechanical support.





Effect of Hypotonic Solution on a Plant Cell





C. PLANT CELLS IN A HYPERTONIC SOLUTION
1. When a plant cell is placed in a hypertonic solution such as 30% sucrose solution, water molecules diffuses out of the cell by osmosis.
2. Water is lost from the vacuole and cytoplasm.
3. The vacuole and the cytoplasm shrink. The plasma membrane is pulled away from the cell wall.
4. The plant cell becomes flaccid and the plant wilts.
5. This process is called plasmolysis.
6. If the plasmolysed plant cell is immersed in a hypotonic solution, there is a net movement of water into the cell. The cell will expand and become turgid again.
7. This process is called deplasmolysis.







Effect of Hypertonic Solution on a Plant Cell








A Simulation of Plasmolysis Process in Onion Cells



A Simulation of Deplasmolysis Process in Onion Cells


A Deplasmolysis Process in a Wilt Salad Leaf.



D. ANIMAL CELLS IN AN ISOTONIC SOLUTION

1. When animal cells such as red blood cells are immersed in an isotonic solution (0.85% sodium chloride solution), water molecules flow across the plasa membrane at the same rate in both directions.
2. There is no net movement of water molecules across the plasma membrane because the concentration in the red blood cells is the same as the concentration in the environment.
3. The red blood cells maintain their shape.








E. ANIMAL CELLS IN A HYPOTONIC SOLUTION
1. When red blood cells are placed in a hypotonic solution (distilled water), water molecules diffuse into the red blood cells by osmosis.
2. The red blood cells gain water and swell.Finally burst because they have no cell wall.
3. The red blood cells undergo haemolysis.






F. ANIMAL CELLS IN A HYPERTONIC SOLUTION
1. When red blood cells are placed in a hypertonic solution (4% sodium chloride solution), water molecules diffuse out of the cells by osmosis.
2. Water is rapidly lost.
3. The red blood cells will shrivel and probably die.
4. This process is called crenation.








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