Aim and background knowledge: - To investigate how different concentrations of sugar solutions affect the osmosis and equilibrium happening in potatoes.

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Aim and background knowledge:

−        To investigate how different concentrations of sugar solutions affect the osmosis and equilibrium happening in potatoes.

Osmosis is the net movement/diffusion of water molecules from high (hypertonic) to low concentration (hypotonic) across a partially permeable membrane.

Equilibrium is when the concentrations on each side of the selectively permeable membrane are equal, and therefore, there is no net change over time and there is equal movement in both directions.

Method:

1.        First, I cut the potatoes into as similar as possible shapes using a potato chipper and a knife and measured the mass of each, picking the shapes which weighed the most similar.

2.        Next, I made the various sugar solutions. This was done by calculating the appropriate proportions in relation to the solution tables. Measuring cylinders were used to carry out this step.

3.        Then, I placed the potato shapes with certain sugar solutions into test tubes.

4.        The test tubes were left for approximately two hours so that osmosis could take place.

5.        The masses of the potato shapes were measured after drying off water residues; this data was recorded in a table.

The variable that was changed was the concentrations of sugar solutions.

Preliminary work and justifications of plan:

The first preliminary work completed was using raisins to obtain a broader understanding of osmosis and equilibrium. We measured the masses of raisins before and after osmosis took place, and chose similar weighing raisins to make sure that the results would be more valid. After osmosis happened, we measured the mass of each raisin again (after drying off water residues) and recorded this information in a table. From completing this work, I have learnt that not only the mass is important when making investigations such as these fair tests, but also the surface areas of the samples used should be taken into consideration. This is because, when the surface area is larger, the diffusion of water molecules through the plant cells increases, and so osmosis increases. However, the surface area of raisins is not directly proportional to its mass. Additionally there is not a very accurate method to measure the surface area of raisins, as their shapes are very irregular (with numerous grooves and ridges) These grooves and ridges mean that water remains in the gaps even after drying the raisins (in order to measure the masses accurately after osmosis has happened).

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During the main preliminary work, I used two different vegetables (potato and carrot) and a couple of different sugar solutions. At first, I found it hard to comprehend the ideas behind osmosis and equilibrium, and apply these to completing an investigation. But after completing the graph (included in coursework) to illustrate the results, I understood the mistakes that I had made and knew that I would be able to correct these in the actual investigation. From observing that a small range of concentrations of sugar solutions made the results not very useful, weak and inconclusive,  I realised that by ...

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