Investigate the effect on length when varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato pieces of the same size.

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                                                      GCSE Biology       Manish patalia

Aim

 

To investigate the effect on length when varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato pieces of the same size. And to find the water potential of potato pieces.

Before I actually planning the experiment, I think that it is essential that I do some research about osmosis, and matters related to it, so that I an make predictions. And work out a way to make this investigation fair, safe and predictable.

Planning my experiment will make it easier for me to know what to do and when. This will help me to get more accurate results.

Hypothesis

Diffusion is defined as the movement of water molecules across a partially permeable membrane from a region of high water concentration to area of low water concentration. This movement has to occur across a partially permeable membrane like a cell wall, which is penetrable by small molecules. Water as a small compound can easily diffuse through but larger molecules wont be able to penetrate the membrane.

A partially permeable membrane is something that has tiny holes in it. So in fact only water molecules can pass through them and bigger molecules like glucose can’t.

This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecule. A potato contains starch but it is not osmotically active (insoluble). This will affect the water potential of the cell’s cytoplasm.

In a partially permeable membrane like potato cells the water molecules can actually pass both ways through the membrane, like two way traffic. In some cases there may be some different amounts of water on each side of the membrane. For instance their may be more water outside the potato cells while a potato is placed in a jar of water. In this case because there is more water molecules on one side of membrane then the outside there’s a steady net flow into the region with fewer water molecules, it into the stronger solution.

Diagram below shows the movement of water molecules across a partially permeable membrane like a potato.

The diagrams below show the movement of water on different water and concentrate circumstances.

                                         Darker the colour the higher the concentration

                                                                                                                     

                                                                                                     

This diagram shows that if there is less water molecules outside the cytoplasm then the water will flow out along the diffusion gradient. The potato cytoplasm will concededly shrink due to the loss of water. I predict this sort of water movement will happen when a potato piece is placed in a solution which is highly concentrated with sugar. The potato cells become more flaccid as water content is low in the potato cell area due to the loss of water.

 

This diagram shows that if the cytoplasm is more concentrated with sugar and starch and less with water, the water along the diffusion gradient will flow into the cytoplasm through its partially permeable membrane. This will make the potato expand in size and it will make its cells more turgid.  

In this diagram the sugar solution is equal to concentration in sugar as the cytoplasm and potato. This means that water doesn’t move to a particular side. In this diagram there is a steady net flow of water passing through the cell membrane both ways. I predict that this sort of water movement will happen when I use a sugar solution that is equal in concentration to the potato (0.4 molar). The cell hasn’t become flaccid or turgid in this diagram in fact it has stayed the same due to the equal sugar concentration.  

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The potato cells in my experiment when placed in solutions that contain less water then the water content in the potato will lose water via the osmotic gradient. The Solution will have higher water (ψ).

In pure water potential is 0. Water potential (ψ) is the tendency of water molecules to move from one place to another. Water potential will always move from a place with high water potential to a place where there is less water potential until a equilibrium is reached. If a solute is added to water then it will have ...

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