The Concentration inside Potato Cells

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Ami Broughton 11K

The Concentration inside Potato Cells

Aim

To find the concentration of the inside of potato cells.

Prediction and Background Knowledge

It is hard to make a prediction about what the concentration of the potato cells will be until I have completed my preliminary experiment. By looking at my background knowledge I can see a general idea what will happen during the experiment.

Theory of osmosis: Osmosis is the process by which water molecules move from an area of a low solute concentration to an area of high solute concentration through a semi-permeable membrane to balance out a concentration gradient. When the concentration gradient has been balanced out this is called an equilibrium. Encarta 98 says that osmosis is “the flow of one constituent of a solution through a semi-permeable membrane while the other constituents are blocked and unable to pass through the membrane”.

In my experiment the particles that will pass through the semi-permeable membrane of the potato cells are water particles and the particles that are blocked from passing through the semi-permeable membrane are the sodium chloride particles. Osmosis can work both ways and water is being lost from the potato but the net movement happens with water going into the potato, as shown in the diagram above.

 When osmosis occurs in the potato cells the potato gains water and therefore its mass increases as does its length. The potato cells become turgid and swollen which causes in increase in length and mass, as shown in the diagram:

When turgid, the cells no longer take on water by osmosis as they are full. This is the normal state for cells to be in. If a cell has a weak concentration it loses water meaning it will become plasmolysed, as shown in the diagram. This is what causes plants to wilt as turgidity also gives a plant its shape.

 If osmosis does occur during my experiment it means that there is a difference in concentration between the potato and the sodium chloride solution. The potato will have either gained or lost mass. If there is no change in the mass or length of the potato this means that no osmosis has taken place and the concentration of the sodium chloride solution must be equal to that of the potato cells; an equilibrium between the concentration of the solution and the potato cells has been reached. This is how I plan to find out the concentration of the inside of potato cells.

Factors Affecting Osmosis: Other factors that could affect osmosis are concentration, temperature, surface area, mass and the type of potato used.

  1. If the concentration of the sodium chloride solution is high and the concentration inside the potato cells is reasonably high then the amount of osmosis that occurs will be low. If both concentrations are low then the same will happen. If there is a big difference between the two concentrations then more osmosis will occur.

  1. If the temperature of the sodium chloride solution is quite high then more osmosis will occur. This is because the water molecules have more energy and therefore they have more energy to pass through the semi-permeable membrane. The opposite effect will occur if the temperature of the sodium chloride solution is low. Osmosis will happen quicker so the equilibrium will be reached faster.  
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  1. If the potato has a high surface area then more osmosis can occur because there are more places for the water to pass into the potato. Osmosis will happen quicker so the equilibrium will be reached faster. Mass has a similar effect to surface area on the rate of osmosis.

  1. If the mass of the potato core is less than the other cores then the osmosis equilibrium will be reaches faster. If the mass of the core is higher, then the equilibrium will be reached slower.

  1. If the type of potato used is different ...

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