Candidate no: 0126
Hampton Community College
Osmosis in animals.
Cell membranes behave very like visking tubing. They will let some substances pass through them, but not others. They are selectively permeable membranes.
There is always cytoplasm on one side of any cell membrane. Cytoplasm is a solution of proteins and other substances in water. There is usually a solution on the other side of the membrane too. Inside large animals, cells are surrounded by tissue fluid. In the soil, the roots of plants are often surrounded by a film of water. Single-celled organisms such as amoeba are also surrounded by water. So, cell membranes often separate two different solutions - the cytoplasm and the solution around the cell. If the solutions are of different concentrations, then osmosis will occur.
The picture below illustrates an animal cell in pure water. The cytoplasm inside the cell is a fairly concentrated solution. The proteins and many other substances dissolved in it are too large to get through the cell membrane. Water molecules, though, can get through.
In a solution, the dilute solution and the pure water are each separated from a concentrated solution by a selectively permeable membrane. In the first diagram below, the concentrated solution is the cytoplasm and the selectively permeable membrane is the cell membrane. Therefore osmosis occurs.
Water molecules will diffuse from the dilute solution into the concentrated solution. So what happens is as more and more water enters it, it swells. The cell membrane has to stretch as the cell gets bigger, until eventually the strain is too much and the cell bursts.
The second figure below illustrates an animal cell in a concentrated solution. If this solution is more concentrated than the cytoplasm then the water molecules will diffuse out of the cell. As the water molecules go out through the cell membrane, the cytoplasm shrinks. The cell shrivels up.
Stacey Owen
Candidate no: 0126
Hampton Community College
Stomata
There are thousands of stomata on each square centimeter of the leaf’s lower surface. Together they form a very large surface area through which oxygen and carbon dioxide can diffuse.
Plants have stomata to allow carbon dioxide to enter the leaf for photosynthesis. Unfortunately for the plant, if stomata are open to allow carbon dioxide into the leaf, they will also allow water vapour to leave. Stomata are not open all the time. The diagram (below) shows when stomata are open and closed during a 24 hour period.
Method
The first thing I will do is to collect my equipment. The equipment I will be using is:
- Six test tubes 5. Measuring cylinder
- Sugar 6. Filter
- Potato 7. Scales
4. Potato corker 8. Test tube rack
Stacey Owen
Candidate no: 0126
Hampton Community College
I will place the six test tubes in the rack. I will then label each test tube from 1-6. I will then fill the test tubes about ⅔ with water; I will use the measuring cylinder to make sure I put the same amount in each test tube. Then I will take a potato and the potato corker and take out six potato chips all from the same potato because each potato has grown in different living conditions, also there is lots of different potato species. Now I will try to get the potato to the same length by cutting them. After this I will weigh each potato chip and record the results. I can place 1 potato chip in each test tube. Now I have to measure out the sugar, firstly I will check to see if the scales are on 0 then measure out ½g and put this in test tube 2 because there going to be no sugar in test tube 1. Then measure out 1g and put this in test tube 3, measure out 1½g and put this in test tube 4.finally measure out 2g , put this in test tube 5 and then measure out 2½g ,put this in test tube 6. Then I will leave it for 24 hours. I will then filter the water and just take the potato put it on some tissue and roll it twice and then weigh it and record the
results, I will do this for all the potato chips. Now I can find out whether there has been a decrease or increase in the weight of the potato chip from the original weight. We either had the choose of using 0g,1g,2g,3g,4g,5g of sugar or using 0g, ½g, 1g, 1½g,2g,2½g. we decided the second option because we were told that half the class should do 1 set of measurements of sugar and the other half should do the other set of measurements of sugar, but we thought most the class would do the first one as it basic, so we done the other set but I then repeated the experiment using the other option. I had to make a measurement of each potato chip before and after osmosis had taken place. I tried to make sure my experiment was as precise as I could make it e.g. I made sure I wrote down the right weights by weighing them again, then checking the people books who I will be working with. Also I will put the measuring cylinder on a flat surface, so I make sure there is the right amount and when transferring the water from the measuring cylinder to the test tubes, I will try not to spill any. I try to use the right measurements e.g. for sugar, I used grams and for water, I used millimeters.
Preliminary work
For my preliminary work, I did a small experiment using dialysis tubing. I took a length of dialysis tubing and made it into a sac about 10-12cms long. I filled this sac with strong sucrose sugar solution and tied the ends off. Then I weighed the sac using an accurate weighing machine and recording this mass in grams. I put
Stacey Owen
Candidate no: 0126
Hampton Community College
the sac in a beaker of water and left it for three days. I took it out and dried it after this time had gone. Then I weighed the sac again and recorded this result. Then I worked out whether the sac had gained or lost weight by osmosis. I done exactly the same thing, but filled the sac with water and put it in a beaker of strong sucrose solution and then I recorded the results. Here are the results I got from this experiment:
The sucrose in the dialysis tubing has an increase of its original weight, whereas the water in the dialysis has had quite a large decrease. The sucrose in the dialysis tubing has increased because it had the water trying to coin to balance out the amount of water, the sugar was also trying to balance out the amount of sugar but as the sugar molecules were bigger they could not get out. Whereas the water in the dialysis has had the water going out but the sugar could not come in. Using this experiment helps me to understand what osmosis is and also it helped me to make my prediction below.
My predicted graph:
I can predict that the more sugar, the less the increase or the more the decrease. I think this because of the movement of molecules e.g. in my first test tube I’m putting in no sugar, so all that happens is the water will try to get in to balance it out but the sugar won’t be able to come out because the sugar molecules are too big, so there will be an increase.
Whereas in my last test tube I’m putting in 2½g of sugar, so the sugar will try to come in but it can not as the molecules are too big but the water can come out to balance it out so there will be a decrease. So it will be like what happens in the animal’s cell which I have talked about above.
Stacey Owen
Candidate no: 0126
Hampton Community College
Science Coursework
Osmosis
Results
I made sure I worked safely by being careful when using the knife.
These are the results from my experiment:
Table 1
I repeated the experiment once, here are the results:
Table 2
In the second set of results, I use 1, 2, 3, 4, 5g of sugar and did not go up in half. As you can see in the table of results 2, the weights at the beginning are higher and so after the experiment the weights are also higher. Also there is more of a percentage increase but less of a decrease.
Stacey Owen
Candidate no: 0126
Hampton Community College
Science Coursework
Osmosis
Conclusion
I’ve found out that my prediction was mostly correct. I’ve had to carry out the following calculations:
- working out whether there was a decrease or increase of the original weight
- Working out the percentage by which the weight had decreased or increased.
I’ve drawn a line graph to show the 1st set of results.
I’ve drawn another line graph which shows the 1st set of percentage results.
Stacey Owen
Candidate no: 0126
Hampton Community College
I’ve drawn a line graph to show the 2nd set of results.
I’ve drawn another line graph which shows the 1st set of percentage results.
There is a definite relationship between the two sets of data that I used to plot the 2 sets of graphs. To conclude this, I can say that the movement of water through a permeable membrane is affected by the amount of sugar.
Stacey Owen
Candidate no: 0126
Hampton Community College
The higher the amount of sugar, the more the potato chip will lose its weight. This is because as the sugar gets more, the water in the solution is less able to move to the potato chip, causing water from the potato chip to move to the solution, decreasing its weight.
In the first beaker, the water is more sugary then the inside so the water will come out of the potato chip to balance the amount of sugar out. Whereas in the second beaker, the water is less sugary on the outside so the water will go into the potato chip to balance out the amount of sugar.
If the amount of sugar outside the cell is less than that inside the cell, this means that the solution is hypotonic to the cells of the potato chip.
In the first beaker, the water is more sugary than the inside, so the water will come out of the beaker to balance the amount of sugar. This diagram illustrates what happens.
Whereas in the second beaker, the water is less sugary on the outside, so the water will go into the potato chip to balance out the amount of sugar.
Stacey Owen
Candidate no: 0126
Hampton Community College
Science Coursework
Osmosis
Evaluation
The evidence, I obtained has help me to come to my conclusion above. My results show quite definitely that as the potato chips are in more sugary water they shrink. I’m happy with the accuracy of my results for two reasons:
- The results follow my prediction.
- All the points on the graphs are close to the line of best fit.
I could have made my experiment more accurate if I had taken another set of readings or even several more sets of readings, I would have obtained a better average.
I’m pretty pleased with the suitability of my experiment for the following reasons:
- I was able to get a good and valid set of readings using the equipment and time allowed.
- I made sure that the test was as fair as possible by making sure the amount of water was the same, the potato chips were from the same potato and that there was only one input variable that changed i.e. the amount of sugar.
There was only one anomalous result. It was the 5th result in the first set; this was because it was shorter than the others. So it could not take in as much, so it could not give out as much either. So if I was to do the experiment again I would measure the length of the potato and then take this into account when looking at my results.
Therefore I’m happy that my evidence is accurate and reliable enough to support my conclusion.
To improve and extend this investigation I could use the same method to investigate a greater range of input variables e.g.
- Temperature
- Bigger potato chips
- Sugar (more concentrated)
- Use other materials (different fruits)
Stacey Owen
Candidate no: 0126
Hampton Community College