Osmosis Coursework. Investigation Of The Effect of Different Concentrations of Sucrose Solution on Potato Strips

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Investigation Of The Effect of Different Concentrations of Sucrose Solution on Potato Strips

Aim of Investigation

I aim to investigate if osmosis occurs when potato cylinders are placed in different concentrations of sucrose solution. I will weigh the potato cylinders at the start and then again after three hours to find the percentage change in mass in each different solution. I will plot a graph of my results and from the graph I hope to find the internal sucrose concentration of the potato. This point is where there is no percentage change in mass as the internal and external sucrose concentrations will be equal and therefore there is no concentration gradient.

Scientific Knowledge

Osmosis is defined as ‘the movement of water molecules from an area of high water concentration to an area of low water concentration, across a selectively permeable membrane’ (Collins 1999).

Osmosis is a special type of diffusion, in which water molecules move through a selectively permeable membrane. Because water are small molecules and are able to fit through the gaps in the membrane. The large polar molecules (e.g. Sugar) cannot fit through the small gaps of the membrane, this is what makes it semi-permeable.

When the concentration of water molecules is high and the concentration of the solute molecules is low, this is called a weak / dilute /hypotonic solution.

When the concentration of water molecules is low and the concentration of the solute molecules is high, this is called a strong / concentrated / hypertonicsolution.

When two differently concentrated solutions are divided by a semi-permeable membrane the water molecules will move from the area of high concentration to the area of low concentration via. osmosis (the dilute solution into the concentrated solution), until both sides have reached an equal concentration called the isotonic solution.

Plant Cell in Water

When a plant cell is placed in distilled water (meaning it has a high water concentration) water will move across the selectively permeable membrane into the cell (which has a low water concentration) by osmosis, this results in the plant cell to swell and become turgid. If this is done with potato tissue we would see an increase in volume and mass of the potato tissue because of the extra water.

If a potato tissue is placed in a solution with a low water concentration, water will move out of the cell into the external sucrose solution. In some cases the cell membrane will break away from the cell wall, this is referred to as plasmolysed. The cell will have decreased in volume and mass because of the decrease in water.

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If the potato tissue is placed in a solution with the same water concentration of that inside the cell, water will move out of the cell at the same rate as it enters the cell. In this case the cell will stay its original shape and there will be no change in mass or size. This is called an isotonic solution. This is when the solution inside the plant cell is of equal osmotic potential to the solution surrounding the cell.

Predictions

When I put the potato into water or dilute sucrose solutions I ...

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