osmosis

Topics: Cell wall, Plant cell, Concentration Pages: 15 (2394 words) Published: October 13, 2014
Osmosis in Plants

Outline:

To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size.

Definition - Osmosis:

Movement of a solvent (liquid) through a semi-permeable membrane separating solutions of different concentrations. The solvent passes from a less concentrated solution to a more concentrated solution until the two concentrations are equal.

All cell membranes behave as semi permeable membranes, and osmosis is a vital mechanism in the transport of fluids in living organisms for example, in the transport of water from the roots up the stems of plants.

Further relevant information on potato plant cells:

Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant "stand up" into the sunlight.

When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells

Shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.

When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means "about to be".

Plant cell structure:

Plant Structure:

How does Photosynthesis Work?:

The chloroplasts in the leaf cells convert sunlight into energy for the plant.

Carbon dioxide + water = Sugar + Oxygen

6CO2 + 6H2O = C6H12O6 + 6O2

Water movement in plants:

Xylem cell: Root cell:

The water is absorbed by the root calls and travels up the xylem cells to all the parts of the plant. Water is needed to make very important chemical processes happen, they also support the plant.

Reaction rate theory:

The theory is that different solutions can affect the way plant cells osmoses e.g.

A sugar water solution increases the extent of osmosis compared to just water.

Variables in the test:

These variables can affect the extent of osmosis: -

Heat:heating up the potato chip in the sugar will speed up the reaction and may increase the extent of the osmosis.

Concentration of sugar in solution: The concentration of sugar in the solution is a key factor in increasing or decreasing the extent of osmosis in the plants the more sugary the solution, the greater the extent of osmosis. The more sugar, the smaller the vegetable and the greater the amount of osmosis will occur.

Stirring: stirring the solution will speed up the rate of osmosis. If you leave the solution to react without stirring it will take a lot longer as the cell walls are weakened more with the molecule collisions that would occur.

Increasing surface area: if the potato chip had a larger surface area the extent of osmosis would increase largely. In the experiment the pieces of potato have to be the same size (length, width and even weight).

Other Vegetables: by using other vegetables you can observe how the rate of osmosis differs between them.

Age:by using fresh vegetables instead of old vegetables the extent of osmosis will be greatly affected as the cell walls would be stronger and newer.

PRELIMINARY

Choosing a variable:

It was decided that the concentration of the sugar in the solution was...
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