I have chosen 5 ranges in my practical A-E to get more reliable evidence.
I wanted to see what would happen to the chips when they were placed in strong solution, solutions of medium strengths and solution with no glucose at all. This range would provide more reliable results and a better understanding of Osmosis. I have chosen a measurement of 3cm for each chip because it is easy to fit I the test tube and also any change in length would have been easy to measure.
I repeated the practical twice to get an accurate result and to rectify any mistakes I made in the first reading.
A semi permeable membrane is important because it only allows small molecules to pass through it such as Water. This means if the potato decrease or increase in size it would be the movement of water in or out which is causing it. Osmosis will not occur when the concentration of water is the same on both sides of the semi permeable membrane. When the cell loses water it shrinks and becomes flaccid, when it gains water it increases in size and becomes turgid.
(P8B) Background information
Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
A semi permeable is a thin layer with tiny pores surrounding a plant cell and an animal cell and is known as a cell membrane. Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, Glucose, amino-acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. to pass through.
An area of high concentration of water is either a very dilute solution of something like sucrose or pure water. In each case there is a lot of water: there is a high concentration of water.
In osmosis the movement of water can occur from both directions. This may mean more movement out of the cell, or more movement in the cell, and however water molecules tend to move more from one direction to another, depending on the concentration of the solution inside and outside of the cell.
Method
To complete my practical accurately and to get fair reliable results I have plan each step appropriately to avoid any mistakes that may occur.
I collected my equipment to begin my experiment. There was 3 students in my group including me the other two students were Harry and Edward, to complete our practical we each had separate jobs.
I had to collect the equipment cut the potato chips to 3cm I measured them with a ruler to get an accurate measurement. Then Harry placed the potato chips into the chipper so the chips are all the same size so the test would be fair. Whilst Harry was cutting the chips to size Edward was filling up the test tubes with different concentrations. He used a measuring cylinder so the concentrations were all measured to size. He labelled the test tubes from A-E, A was the strongest solution of sugar and E had no solution of sugar.
After completing the main part of the practical Harry, Edward and I placed the test tube rack with labelled test tubes in them on the window.
Observation
Reading 1
Reading 2
You can see by looking at my table how a strong concentration and a weak concentration affect’s a potato chip over a certain length of time.
Analysis
(A2A) What happened?
After completing my 2 readings in my practical and accomplished my results I identified what happened. I identified that the more volume of glucose there was the more the potato chip would shrink and if there was a weak concentration of water the potato chip would increase in size. This is because water in osmosis moves from a high concentration to a low concentration and if there was a high volume of glucose that would mean the water would be in the potato chip and it would move to a low concentration which would be in the glucose solution because of this the potato chip would decrease as it is lacking water. But in the other hand if there was a high volume of water it would mean all the water is in the solution so the water would move to a weak concentration, which would be the potato chip, and as a result the potato chip would increase in size.
(A4A) line Graph
I have presented my findings in the form of a line graph.
(A4B) Pattern and Trend
As the Mole decreases the change in length increases. This pattern has appeared in both of my readings. This pattern shows that if the lower the concentration the length of the potato chip will increase.
For example
When the concentration was 1 mole
The change in length was - 0.2 cm
When the concentration was 0.0 mole
The change in length was + 0.3
This example explains the Pattern I have identified because you can see that the bigger the mole the smaller the size of the chip and the smaller the mole the bigger the chip.
(A6B) Conclusion and scientific knowledge,
I have found out from my table of results and my line graph that if a cell is places in a strong concentration, the cell will decrease in size due to the water from the potato chip moving to the glucose solution.
If you reversed the experiment and placed a cell into a weak concentration the cell will increase in size due to the water moving from the glucose solution to the potato chip. You can see that if I reverse the experiment you will achieve opposite results.
(A6B) Scientific Theory
If you place a cell into a strong concentration of water, using osmosis we know that water will move from a high concentration of water to a low concentration of water. So as there is a strong concentration this means that is more water on the potato chip than in the glucose solution and as a result, the water would move from the potato chip to the glucose solution where it a low concentration of glucose because of this the potato chip will decrease in size because the potato chip has lost plenty of water.
If you put a potato chip into a weak glucose concentration that means there is more water in the glucose solution. Using our knowledge of Osmosis we know that water moves from a high concentration of water to a low concentration of water. As a result the potato chip would increase in size as it has gained plenty of water.
(A8A) Detailed Scientific Theory
Osmosis is the movement of water from an area of high water concentration, through a semi permeable to an area of low water concentration. In Osmosis, the movement of water can occur from both directions. There may be more movement out of the cell, or more movement into the cell, and sometimes the net movement will be balanced. However water molecules tend to move more from one direction to another, depending on the concentration of the solution inside and outside of the cell.
For the 0.5 mole concentration the net movement of water was balanced because water concentration was the same on both of the semi permeable membrane.
The potato chips that decreased in size were because they were placed in a strong glucose solution, which meant there is more water in the glucose solution than on the potato chip.
The chips that increased in size was because they were placed in a weak glucose solution which means that there is more water in the on the potato chip than there is in the glucose solution.
(A8B) How does the result support or undermine my prediction
In my prediction I predicted that if the chip were placed in a strong concentration the chip would decrease in size. Based on my table of results and my line graph my prediction was correct, because the chip that was placed in a strong concentration did decrease in size and the potato chip that was placed in a weak concentration increased in size.
Evaluation
(E2A) Comment on procedure
Overall I think I completed my practical well but I encountered some difficulties such as:
- Cutting the potato chips to 3cm and to keep them very accurate.
- Measuring the final length of the potato chip.
- I found it hard to find out my change in length.
I overcome these problems but if I conducted these problems correctly I may of got different readings.
(E4A) Accuracy
I think I focused on my method fairly accurately as my results were not odd and I was able to draw a line graph with all the points fitting perfectly.
Looking at my line graph you can see the line is like a symmetrical pattern there is a curve on the positive side and the negative side of the line graph I think I was very accurate when completing my practical.
(E4B) Suitability of procedure
I think I used a suitable procedure bit I have some improvements that I would of liked to conduct in my experiment to give me a more accurate and reliable result. The improvements I would like to add was that
- Could of measured my chips more accurately.
- I could of used a wider range of readings instead of 5 I could of used ten so the mole would decrease by 1/10 each time.
- It was difficult to measure the solution with a measuring cylinder so I think I should of used a pipette as it has a smaller measuring scale which would make the result more accurate.
(E6A) Reliability of evidence
The time I leave the chips in the glucose solution affects the process of Osmosis.
The time affected Osmosis because when I came to take the chips out of the solution I had to take them out one at a time so some potato chips stayed in the solution longer than others.
I tried to keep all the variables the same for example:
- Temperature
- Volume of solution
- Size of chips
I had no control over the temperature as the test tubes that the potato chips were placed in were left overnight in a classroom and the temperature may of decreased by a degree or increased.
(E6B) Improvements to further work
It was difficult to keep all the experiment accurate and to achieve reliable results but I think I have completed the experiment accurately but I have realised some mistakes or improvements that I would of liked to make to my experiment such as:
- Measuring the change in length I could of overcome this problem by leaving the potato chips in the solution longer and maybe by using a wider range of results.
There are no other major improvements I would like to add to my work so overall I think I have worked hard sensibly and independently.
By Ricky Gill 10T
Science Coursework
Mrs Gordon
