If the solution is heated up it will increase collisions between the water molecules and the other molecules therefore making them dissolve faster. This happens because the heat is acting as a Catalyst and is speeding up the particles movements.
The more time I give the reaction, the more time the cell will have to grow, and become turgid, or to shrink, and become flaccid.
- Surface area of the potato:
If the potato has a large surface area it means that there will be more surface for osmosis to take place.
If there is a higher or lower concentration of water there will be more chance that the potato chip will grow to be turgid or shrink to be flaccid.
- Concentration of the water:
The concentration of the water can affect the rate of reaction because if there is more salt in the solution, then the membrane will try to dilute it more therefore using more water and making it flaccid.
In this piece of coursework I will be varying only the concentration of the water and how it affects osmosis. The concentration of the water is the most important variable in the experiment as it is what varies what goes in and out of the semi-permeable membrane. The concentration of the water can be controlled quite easily by simply putting in the right concentration of water into each beaker, making sure that the same volume of water is in each one.
Hypothesis:
I predict that as the salt concentration increases, the length of the potato chip will decrease. My reasoning behind this, is that the higher the concentration of glucose in a solution, the lower the concentration of water. When the potato chip is put into the solution, it will, by osmosis lose some of its water, and the water will diffuse into the solution of glucose, causing the potato chip to lose water, thus decreasing in length.
Water potential is defined as “the tendency of water to enter or leave a cell”. Water moves from a region of high water potential to a region of lower water potential. A crucial point to learn is that the highest water potential is 0. All other water potential values are negative numbers and water moves towards the region with the more negative water potential.
Water potential is measured in kilopascals.
However, if a potato chip is placed into a solution of 0% concentration, it should gain length. This is because the solution has more water potential than the potato chip, and so water moves from a region of high concentration (the solution) to a region of low concentration (the potato chip.)
Fair Test:
Except for the variables everything else that could be changed must be kept the same like length of potato, size of borer etc.
Apparatus:
Knife,
White Tile,
Borer,
6 plastic cups,
Ruler,
0%, 2%, 4%, 6%, 8%, 10% Sugar solutions
Method:
1. I took an average sized ground potato and checked that it was both healthy and hard.
2. Using a borer I carved 18 pieces out of the potato and cut each one into an even block approximately 24mm on a white tile.
3. Using a scalpel and ruler I cut the potato into chips that were 24mm long. I had to be very careful whilst cutting the potato, as the scalpel is exceptionally sharp. I then had 18 chips.
4. Taking 6 plastic cups I lined them up and labeled them 0%, 2%, 4%, 6%, 8%, and 10%.
5. Using a measuring cylinder I measured out 15mls of each sugar solution, which I then poured into the corresponding plastic cups.
6. I swiftly put 3 potato chips into each cup and then left them for 24 hours. 3 chips were used to create an average, which would give me a better set of results and more accurate graphs.
8. After 24 hours I set out some paper towels with which I was going to dry up the solution once I was done and I drew up a basic table for my results.
9. When I was ready I drained out the solutions in the sink and placed all the chips on the paper towels in the order I had put them in the plastic cups as to not confuse myself as to which chip came from which solution.
10. I dried each chip with the paper towel and then placed each one on the tile for measuring.
11. Each potato chip was measured accurately and I noted down the length in my book.
Results Table
Conclusion:
To conclude this experiment, I can say that the movement of water through a selectively permeable membrane is affected by concentration of sugar solution. The higher the concentration of sugar solution, the more the potato chip will lose its length.
Because water molecules have kinetic energy, they are constantly moving around in gaseous or liquid form, moving randomly from one place or another. The greater the concentration of water molecules in a system or solution, the greater the total kinetic energy, and the higher its water potential. This means, that as the concentration of glucose increases in a solution, the concentration of water decreases, lessening the solution’s water potential, and lessening its ability to move between solutions by osmosis. Relating this to the potato chips: basically, as the concentration of glucose in each solution increases, the water in that solution is less able to move to the potato, causing water from the potato to move to the solution, decreasing its length, weight and width.
An Osmotic system is established when a semi-permeable membrane is placed between two solutions. In biological systems osmosis is the exchange of water between the toplasm and the surrounding medium, with the plasm membrane being the semi- permeable membrane.
In the living cell, both the cell wall and plasma membrane determine the permeability of the cell, but the latter of the two is the less permeable of the two. The ability of a substance to pass through these barriers is known as the permeation of the substance. Since not all substances may pass into or out of the cell, the cell surface is known as selectively permeable or as a semi permeable membrane. The semi permeability varies from cell to cell and under certain conditions. Water molecules alone permeate freely, but ions do so more slowly, many large molecules and no electrolytes, such as sugars, do not move at all. This indicates that temperature could also affect osmosis. A solution in which the concentration of salt is greater than that inside the cell is called a hypertonic solution and will cause a cell to become Plasmolysis. An example of this in my results is the test at 1 molar. In other words, it becomes dehydrated and loses water through Plasmolysis. If the concentration of the salt solution (in our case Glucose solution) outside the cell is less than that inside the cell, this means that the solution is Hypotonic to the cells of the potato chip. The water will diffuse into the cells, making it turgid. This would explain why potato chips put into a solution of 0 molar seemed very firm compared to the potato chip used for 1 molar, this was because the cells of the potato had lost their turgor, and had become flaccid.
Evaluation:
When it came to accuracy during this experiment, it was extremely difficult to maintain. For example, we had to, for as much as possible, keep each potato chip the same surface area. However, putting this theory into practice wasn’t easy. Even if you cut three potato chips, each measuring 24mm, it was very unlikely that they would all be the same length and width. This inaccuracy was due to human error, it is very difficult to make 18 potato chips exactly the same. In future, I would make a template, or use a cutter to make all my potato chips the same.
Another inaccuracy was when we put the potato chips into the solutions, because it was impossible to not leave a small interval between each test tube. The first test would have been going for a few seconds longer than the last. In future I will time each individual potato chip and leave 1-minute intervals, which then will give me time to immerse all 18 pieces. Therefore it will then give me time to remove each potato chip after 24 hours making it a fairer test.
I could extend this Coursework by investigating osmosis with a different factor as opposed to concentration of water. I could investigate the effects of temperature, surface area or weight on Osmosis. This would give me a very clear understanding and knowledge of osmosis in potatoes.
