Therefore, I must take into account that using some concentrations of solution may give me no affect at all on the potato.
Preliminary Work
Before carrying out this investigation, I looked at similar experiment, which involved changing the concentration of sugar. The graph below shows the results of this experiment.
The graph on the previous page shows that as the concentration of sugar solution increased the length of the potato decreased.
(Fair Testing) The concentrations used were of low concentrations and increased in small intervals. In addition, the change in length of the potato was measured in millimetres. Using this information, I have decided to use a larger concentration increasing in greater intervals. Using these moles will enable me to measure the length of potato easier ensuring that I will get accurate results. It will also enable me to get accurate results because I have used moles which will give me large differences in results therefore they will not be too similar.
To see the affect of osmosis on a potato I could not only look at the change in length but also the weight. This will help me draw a firm prediction and conclusion.
Prediction:
I predict that as the concentration of the sugar solution increases the rate of osmosis will also increase therefore the potato will shrink or decrease in length.
Hypothesis:
I believe this prediction because as the concentration of the sugar solution increases the water concentration in the sugar solution will decrease. This means that the water in the potato will move out because the water in the potato will be of higher concentration inside the potato than outside in the solution. This can be explained using the theory of water movement that water moves from high concentration to low concentration. Because the potato will shrink, I think that the weight of the potato will decrease because water will move out therefore the mass will be lower.
I also predict that when the potato is put into the distilled water the potato will expand or increase in length because there will be a higher concentration of water molecules in the distilled water than inside the potato cylinder. Therefore, water will move in (from high concentration to low concentration). This will also increase the weight.
From my preliminary research, I found that using a certain concentration would show no change in the potato’s length or weight. Therefore, I also predict that when the potato cylinders are put into the low concentrations of sugar solution it can increase in length from its original size.
The graph used in my preliminary work also supports my theory. The length of the potato in the graph decreased as the concentration of sugar solution increased.
Fair Testing:
This will be a fair test because the factors I have described in my preliminary research will remain the same apart from the factor I am changing; the concentration of the sugar solution.
I will do this by cutting the potato cylinders length equally ensuring that they are all the same length and weigh the potato cylinders accurately.
I will also vary the sugar concentrations 5 times and repeat the experiment 3 times.
Apparatus:
Potato
Ruler
Scales
Cork borer
Knife
Beakers
Sugar solution – 4 concentrations: 0.5M, 1.0M, 1.5M, and 2.0M
Distilled water
Stopwatch
Measuring Cylinder
Tongs
Diagram:
Method:
- Use the cork borer to cut 15 cylinders of potato.
- Cut the cylinders so that they are all the same length,
- Weigh and measure the length of one of the potato cylinders and record the result.
- Pour 75ml of each concentration of sugar solution into separate beakers. Also, pour 75ml of distilled water into a separate beaker.
- In each beaker put three potato cylinders. Start stopwatch and leave for 20 minutes.
- After 20 minutes take the potato cylinders out making sure that they have not mixed with potato cylinders soaked in other concentrations.
- Measure and weigh the potato cylinders and record the result.
Safety:
There were no major safety precautions that needed to be taken during the experiment. I used the cork borer and knife safely and carefully.
Results:
The original length and weight of the potato cylinders before being put into the solutions were 3.6cm and 1.5g respectively.
The formulas below show how I calculated the average of the length and weight of potato:
Average length (cm) = (a + b + c) / 3
Average weight (g) = (A + B + C) / 3
Graph: (see next 2 pages)
Conclusion:
My results show that when the potato cylinders were put into distilled water and in 0.5M concentration of sugar solution, it had increased in its length and weight. At about 0.75M in the graph no change had occurred (osmotic potential – it remained its original length) to the potatoes length but beyond that point the length had decreased.
A similar pattern is shown on the graph showing the weight of the potato. The weight had increased in weight when it was put into water and remained larger than its original weight till it had reached 0.625M where the weight had decreased after that point.
This information shows that as the concentration of sugar solution increased the potato cylinders had decreased in weight and length. This supports my prediction.
This change had occurred because as the sugar concentration increased the osmosis rate had also increased. The balances of water molecules were becoming more and more uneven. Therefore, the difference in concentration made the water in the potato move out in greater amounts as water moves from a high concentration to a low concentration.
The theory about the osmotic potential I had made in my hypothesis had been seen in my results. I was correct that there would be at some point where no change would occur or that in some solutions its weight and length may still increase. Referring to my preliminary research it can be explained that there may have still been a higher concentration of water in the sugar solution than inside the potato causing water to move into the potato.
Background Work: A solution is a solute dissolved in a solvent. For example a sugar solution contains sugar (solute) dissolved in water (solvent). Water is a good solvent. In most biological solutions the solvent is water. If we looked at the solutions with a very powerful microscope, we would see the solvent is water. If we looked at the solutions with a very powerful microscope we would see that the solvent sugar end is weaker than side A. Osmosis is the diffusion of water molecules from a region of higher water concentration to a region of lower concentration through a selectively permeable membrane. It is important to remember that in osmosis, it is only the water molecules that move. Solutes stay in place.
Uptakes & Transport of Water in Plants:
All cells absorb water by osmosis. The cell membrane in plant and animal cells is a selectively permeable membrane. Plants absorb water from the soil through delicate root hair cells close to the tips of their roots. These cells give a large surface area for the absorption of water.
Key Facts:
- A solution is a solute dissolved in a solvent.
- Osmosis is the diffusion of water molecules from a region of higher water concentration to a region of lower water concentration through a selectively permeable membrane.
- Water enters a plant through root hair cells by osmosis.
Did You Know?
Poisoned by water- Osmosis affects all living things. A man from Scotland was admitted to hospital in a come. Docters discovered that he had drunk too much water. His blood plasma had become dilute. As a result, his brain cells had taken up too much water by osmosis and had started to burst, causing him to pass out. When he woke up he had drunk too much water to swill round a painfull toothache.
