Find out the concentration of the cell contents of a potato

Introduction

Osmosis is the diffusion of water from a lower concentration of solute to a higher concentration of solute through a partially permeable membrane. This lets smaller molecules such as water, pass through but does not allow bigger molecules through. The molecules continue to diffuse until they reach a balanced state, where no area has a higher or lower concentration than any other.

In a high concentration of water the amount of sugar solution is low. This is called a weak/dilute solution. In a weak concentration of water the amount of sugar solution is high. This is called a strong/concentrated solution.

When a semi-permeable membrane divides two solutions, the water will move from the area of high concentration to the area of low concentration, until both sides are equal.

Aim

To find out how much sugar concentration there is in a cell of a potato. This means I will put the potato cylinders in different solutions of different concentrations.

There are also other factors involved, these are:

Temperature of water
Size of potato cylinder
Mass of potato cylinder
Volume of solution potato cylinder is in
Type of potato
Time left in solution

Fair Testing

If this experiment isn’t a fair test, we will be collecting the wrong results, which can lead us to the wrong conclusions. To conduct a fair test I will ensure that the experiment is carried out at room temperature. The size of the potato is an important factor, as the amount of weight lost or gained will alter. Also the potato cylinders will be weighed before and after the experiment to see if osmosis has taken place. The type of potato I will use will stay the same as different potatoes may absorb at different rates.

Planned Method

A range of sugar solutions will be arranged with concentrations……………..

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Planned Method

A range of sugar solutions will be arranged with concentrations……………..

Sections of potato will be cut with a scalpel and measured with a ruler. This has to be done carefully as the difference of surface area may allow more or less osmosis to occur. The mass of each cylinder will be weighed to ensure consistency. I will do each experiment three times so that I can take an average for each sugar solution. By doing this I will receive more accurate results and therefore draw up a more accurate conclusion. I will also use 20 ml of each solution and of tap water. The potato cylinders will then be left for 15 minutes. When the cylinders are removed I will clean them with a paper towel, to remove excess moisture, and then re-weigh them.

Prediction

For this investigation, I think the lower the concentration of the sugar solution in the beaker the larger the mass of the potato will be. This is because the water molecules will pass from a high concentration (the water) to a low concentration (the potato cylinder). This means that the potato in higher water concentrations will have a larger mass than in higher sugar concentrations.

Apparatus

Potato
Sugar solutions x5- 0%, 1%, 2%, 3% and 4%
Tap water
Cork borer
Measuring cylinder
Tile
Beaker x5
Knife
Ruler
Digital scales
Clingfilm

Method

1. Bore a hole through an average sized potato.

2. Using a scalpel and ruler I cut the potato into 5 equal pieces measuring 2cm long.

3. Using a measuring cylinder, I measured out 100ml of water and put it into each of the beakers.

4. I then weighed the sugar content needed by using digital scales. This varied starting with 1g for 1% of sugar, then 2 grams for 2% of sugar etc. These weights were then recorded.

5. I put each potato cylinder into the different beakers containing the sugar solution. These were labeled so as to not get confused.

6.We covered the tops of the beakers with clingfilm so that oxygen would not interfere with the experiment.

7. After 48 hours, I drained out the solutions and placed all the potato cylinders in the order they were in the beakers, so not to confuse myself.

8. I dried each potato and placed it on the scales to be weighed.

9. Each was measured accurately and recorded.

10. The potato cylinders were weighed twice as to gain an average for my results.

Results and Conclusion

My graph shows that the mass of the potato cylinders before the experiment are roughly more or less the same, whereas as after the experiment, their mass decreases more as a result of which solution it was in, e.g. - high sugar solution= decrease in mass.

My results show that the potato cells increase in mass solutions in high concentration and decrease in mass in solutions in low concentration. When the concentration reaches above 3%, there appears to be no further mass loss, this is because the cell is fully plasmolysed. This is called the isotonic point, when the potato is neither increasing nor decreasing in mass. This is when the potato cannot expand and take in any more water.

The graph shows that there is an obvious decrease in mass during the experiment, which proves my hypothesis as being correct as the higher the sugar concentration the more mass lost.

On my graph I have marked the point where the graph line crosses the place on the axis where the potato neither loses nor gains mass. This happens when the concentration of the sugar solution is 3%, so therefore the content of the potato is 3%.

Evaluation

In my opinion the experiment went well. I gathered a sufficient quantity of results that allowed me to create an informative graph. The time used for the experiment was a good choice as it gave enough time for osmosis to occur. The amount of concentrations was about right, but if I were to repeat the experiment I would maybe use higher ranges.

In my opinion the cutting of the potatoes was the hardest part as although I was only recording the mass for my results, it could have affected the surface area and therefore the general rate of osmosis.

Through my findings I did not find any anomalies. The only possible incorrect things could have been that on removing the potatoes from the beakers, one could have been more dried more thoroughly than the others and so would have had excess water, this would add to the mass. If the experiment was repeated I would find another way to dry off the potatoes that would ensure they were dried the same way for the same amount of time.

To extend this experiment I could by looking at the potato cylinders through a microscope, this would enable me to see the cells in greater detail and draw some more observational drawings.

However I thought the experiment went very well, and I was pleased that the results backed up my initial prediction.