Variables:
Independent Variable:
In this experiment I will have only one independent variable, which I will change though out the experiment. The independent variable will be the sugar solution that the potatoes are placed in, I will first of all do a test to see what concentration
Dependent Variables:
I’ll have several Dependent variables in this experiment to try and help keep it a fair test. The first one being that I’ll keep all the other variables the same (e.g. Mass). I’ll also make sure that I use all the same equipment (e.g. the same beakers) and the last dependent variable will be that I will use only sugar and water to make the sugar solutions. The reason for keeping all of these variables the same is to help keep the experiment fair, if something else was added into the solution it could affect the results
Hypothesis:
Osmosis is where water passes though semi-permeable membranes from high concentration to a low concentration. What I mean by a semi-permeable membrane is a cell membrane that only allows very small molecules though e.g. Oxygen, water, Carbon Dioxide etc but don’t let large molecules though e.g. starch etc. So to osmosis is the passage from a dilute solution to a more concentrated solution though a semi-permeable substance.
Now to explain how osmosis would affect a plant cell if placed into a water concentration. If the cell was placed in a water concentration that was of a higher concentration of the cell, then the cell would grow in size because water would enter the cell, whereas if the cell was a higher concentration the water concentration it was placed in, the cells size would decrease because water would leave the cell and go into the water concentration it was placed in. If the cell and the water were of the same concentration, then there would be no change in mass.
From knowing this I could estimate that the point where they’ll be no change in mass be around 5% or slightly over.
Equipment:
- 5 x 100ml beakers
- 15 x Potato Chips
- 5 pieces or red and 5 pieces of blue cotton.
- 450ml of Water
- 50g of Sugar
- A clean scalpel knife
- Electronic scales
Method:
1.) Firstly we will cut each chip to be 4cm long and 1cm in depth and width to make sure that each chip has the same amount of surface area, this will mean that each chip will have the same amount of cell membrane in contact with the solution making it a fair test.
2.) Then we’ll weigh each chip on a ser of electronic scales and rounding it off to just 2 decimal places.
3.) We’ll then tie a piece of red cotton around 5 chips and 5 pieces of red around another 5 chips. The reason we use cotton instead of pen or any other way of marking the chip is because it firstly causes the least damage to chip but it also covers the least surface area.
4.) Next we’ll make 6 sugar solutions, from 0% to 25% going up in increments of 5%, places in 100ml of water in beakers all the same size. By making the beakers the same size you know that each one will have the sugar spread out evenly.
3.) Then the potato chips will be placed in each beaker at the same time, insuring that it will be a fair test.
4.) The beakers will then be left for 24 hours, giving them enough time to absorb or release water but not too long so they don’t plasmolysed or become too turgid.
5.) After the 24 hours, we’ll remove the potato chips from the water solutions and roll then on paper towel but not pressing down on them, just to remove any excess water off them. The reason we don’t press on the chips is because if we did we might squeeze out water from inside them making the test unfair.
5.) Then the potato chips are weighed to 2 decimal places (in grams) like before to give us accurate results.
6.) Then we’ll calculate the change in mass in both grams and percentage.
Fair Test:
When I do this experiment I will be doing several things to make sure that it’s a fair test. The first one being that I’ll make sure all surfaces and sizes are the same on each chip. Also I will have to make sure I keep the sugar solution all in the same place because otherwise they would be different conditions and this could effect me results, firstly because the of temperature which could effect the conditions and results of my test making it unfair. Another thing I’ll keep the same is the amount of time in which there kept in the sugar solution because leaving some in for longer than other could also affect the results. Finally when drying the potato chips afterward I will make sure not to apply any pressure because if I apply pressure it could also effect the results.
Analysis:
I have determined that the potato chips have approximately 5.75% starch content. I have been able to work this out because on my graphs the line of best fit crosses 0 on the y axis at 5.75%. The graph was of a negative gradient.
Osmosis is the way water in which moved around a plant. It is the movement of water from a high water potential to a low water potential through a partially permeable membrane. A high water potential is something with a lot of water and not much of any other substances e.g. salt or sugar, whereas a low water potential is something with a lot of the sugars or salts and not as much water.
For example if you put a plant sell into a sugar solution there are 3 possible outcomes:
1) If the water has a high water potential, for example a sugar solution of 0% then the plant cell would gain water though osmosis and increase in size.
2) If both the sugar solution and the plant cell were of the same concentration then they’d be no net change and the cell would stay the same size and weight.
3) If the water was of a low water potential (very concentrated e.g. sugar). Take for example a sugar solution of say 20% is of a low water potential so it would cause the plant sell to shrink and lose water.
Evaluation:
The results from the experiment could have been a lot accurate if we could of looked at other possibilities and elements that could of effected. Take for example by putting the beakers in a set temperature for the time, or in or out of direct sunlight. By doing these in the test it would have meant that the results could have been more accurate and wouldn’t have been effects by any other variables that we didn’t include into the experiment. Also some of the results in my results might have been affect by other things which could of happened during the test that i wouldn’t of meant to of happened, take for example if one of the potato chips was leaning against the side of the beaker, which would of consequenced in that potato chip not having as much contact with the sugar solution as the rest.
If I was to continue this investigation any further or re-do the experiment I would like to look into testing it going up by 1% each time between 5% and 10%, and then I would have an even better idea of exactly what the amount of starch is inside the potato chip. Another thing I would of like to of done is to of maybe tried more potato chips instead of 3 maybe tried 5, which would help me in being able to reach a more exactly amount and would give me more reliable results because I would be able to work out a more accurate average. Finally I would also have liked to of looked into trying this experiment in a different place, say out of view of the sun from the window or in a place where I could set the temperature to a certain amount.
The last thing I would like to change if I could do this experiment again is putting the potato chips at an angle or all lay across the bottom of the beakers, so then I would be able to get even more accurate results and not have some potato chips with more contact with the sugar solution than others (Like shown in diagrams). It would also help me get results which are more reliable.