When measuring the mass change in the potato cells, we will need to make sure that the potato cells start off at the exact same mass, length and surface area. These variables need to be kept the same in order for the test to be fair. If the potato cells started off with different surface areas or lengths, we would not be able to measure any change accurately. Surface area also effects osmosis. If a cell has a larger surface area, the rate of osmosis will change due to the fact that osmosis will have to take place in more areas. This is why surface area must be controlled. Another factor that could affect osmosis is temperature. If the temperature is higher, the rate of osmosis will be higher also. This is because, in a plant cell, when the temperature is higher the plant photosynthesises much faster in order to create as much food and energy as possible. This means that they need to take in water at a faster rate, hence, the rate of osmosis increases. This is why we need to control the temperature when carrying out our experiment.
Prediction
I predict that our experiment will prove that the higher the concentration of sucrose is, the higher the rate of osmosis. Although a higher percentage of sucrose in the solution will mean a loss in mass, the rate of osmosis will still be higher because the more sucrose you add to the solution, the weaker it becomes. Therefore, there will be a higher concentration in the potato cell and the water particles will travel to the sucrose solution. If we have less sucrose in a solution, the potato cell will gain mass because the solution will be of higher concentration than that of the potato. Therefore, the potato will take in water, but not as fast as it would when giving out water because of high sucrose concentration.
I predict to get a graph that looks something like this:
Safe Test
There are many aspects that one needs to be aware of while doing any experiment. Safety is a very important aspect, if safety is taken lightly, then accidents are likely to occur. Things that one needs to be aware of, are:
Wear safety goggles at all times
This is so no chemicals can come in contact with the eyes. The eyes are a very sensitive area and can be irritated easily, goggles must be worn at all times, even when the chemicals have not been brought out.
Tie back long hair
Hair must be tied back because it can easily catch fire. A Bunsen burner will be used in this experiment so all hair must be tied back and all sleeves must be rolled up, to keep as far away as possible from the fire.
When picking up bottles of acid, never hold by the lid
If a bottle of acid is held from the lid, and it hasn’t been properly put on, the acid could spill all over the person holding the bottle, which is extremely dangerous. And can burn through clothes to the skin.
Stand up when doing an experiment
When doing any experiment, one must stand at all times. If a bottle of acid is spilt during the experiment and one is sitting down, it would be extremely difficult for one to move out of the way quickly. But if one is standing, then one can move back at ease, avoiding any hazards.
Never put anything in your mouth when doing an experiment
When in a lab, nothing should be eaten or drank, this is a health hazard with no experiment. But becomes more dangerous when there is a experiment going on, chemicals are in the air and can get into the food or drink. This applies for fingers as well. Nothing should be put into ones mouth during an experiment.
Report any accidents to the teacher
As soon as an accident happens, the teacher should be notified immediately. They can make sure nothing is done to increase the health/safety hazard, and can sort out the problem quicker than any student can.
If all the above aspects are taken into consideration, the experiment will be risk free, and successful.
Fair Test
Whenever an experiment takes place, some variable need to stay, but some need to change. In order to make this experiment fair we need to keep certain variables the same every time we do a test. Variables which we need to keep the same are:
Time in which change of mass is measured
This needs to be kept the same because if the time is changed in each test, one would have no idea when the mass changes. The times must be kept exactly the same.
Shape of potato
This must be kept the same, because if different shapes are used, it will affect the end result.
Starting mass of potato
The starting mass must be the same to insure the test is fair, if they are all different masses, it will be hard to say which solution created the most mass change.
Temperature
The temperature must stay the same to insure that the solutions are not affected by the change in temperature.
Volume of sucrose solution used each time
The volume must stay the same so one can monitor the mass change accurately.
If these variables are not kept the same it would influence our results and make them inaccurate.
However, we will also be changing some variables to enable us to obtain the results we need. We will be changing the concentration of sucrose in the sucrose solution, so that we can see how the change in mass varies depending on the concentration of sucrose in the solution.
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Preliminary Investigation
Aim
To decide three aspects of the experiment:
- The most appropriate time to use when measuring change in mass.
- What shape of potato works most effectively.
- What range of sucrose concentrations to use.
First we decided to choose the emersion time:
Method
- Set up apparatus needed in preliminary work.
- Measure out 25cm³ of pure (distilled) water and pour into a test tube.
- Measure out 25 cm³ of 80% sucrose solution and pour into a second test tube.
- Cut out two chunks of potato, measuring them to make sure they are the same mass.
- At the exact same time, drop a chunk of potato into each test tube and start the timer.
- At regular intervals (e.g. every 5 minutes) stop the timer, and check the change in mass for both potato chunks. Do this for an hour until you have all your results.
- Choose the most effective time to use
Results
The time that showed the largest mass change in both pure water and 80% sucrose was 30 minutes, so we decided to use 30 minutes for our immersion time.
We then decided to choose on the potato shape:
Method
- Set up apparatus needed in preliminary work.
- Measure out 25cm³ of pure (distilled) water and pour into a test tube.
- Measure out 25 cm³ of 80% sucrose solution and pour into a second test tube.
- Cut out two fat cylindrical shapes from the potato of the same mass.
- Drop one in each test tube and time for 30 minutes.
- Record results of change in mass.
- Repeat steps 2 to 6 using a cube shape instead of a fat cylinder.
- Repeat steps 2 to 6 using a cylinder shape.
- Choose the shape that gives the best results.
Results
We have chosen to use the cylindrical shape because it shows a good amount of change in mass in both pure water and 80% sucrose, and the results show that it is a relatively equal change in mass in both solutions.
We then decided to choose the concentration range:
Method
- Set up apparatus needed in preliminary work.
- Measure out 25cm³ of sucrose solution with a concentration of 0.01%.
- Using your chosen shape of potato cut a chunk out and drop it into the solution.
- Time for 30 minutes then measure change in mass and record results.
- Repeat steps 2 to 4 using concentrations 0.1%, 1%, 10%, and 80%.
- Choose the most effective concentration and centre your range on it.
Results
*= Anomalous result
We have chosen to use a range of results going from 5% to 15% sucrose. We have chosen this range of concentrations because we want to find the sucrose concentrations nearest to that of the actual concentration in the potato. To do this, we need the percentages that are nearest to 0. From the table above, we can see that at the concentration of 1% sucrose, the potato gained 0.14 grams, and at 80 it lost 0.12 grams. We can assume that the potato will be losing mass, or at least gaining very small amounts of mass at 10% sucrose. Therefore we want concentrations above 1% and close to 10%.
***
The Effect of Sucrose Concentration on
Osmosis
Method
- Set up apparatus needed.
- Measure out 25cm³ of one of the chosen concentrations and pour into a test tube.
- Cut out chosen shape of potato, measure on a top pan balance.
- Drop into sucrose solution and time for 30 minutes.
- After 30 minutes, measure change in mass and record results.
- Repeat another two times for accuracy.
- Repeat steps 2 to 6 with all other chosen concentrations.
If I follow this method, I should have accurate results, and a successful experiment.
Apparatus
The apparatus that I will be using are as follows:
Results
Below are various tables showing the results we found when carrying out our investigation. We tested each concentration of sucrose solution three times, and have found an average from these results. Because we did the experiment three times, to obtain an average – more accurate results, the results were set in four separate tables: first test, second test, third test and mean change in mass:
Test One
*These results do not fit in with the other two tests; they were most probably taken down incorrectly. Therefore, I have decided to disregard them from the mean change in mass, as it would make the results inequitable and ambiguous.
Test Two
Test Three
Mean Change in Mass
Here is a graph presenting the results I gathered during my experiment:
On this graph, we can see that test one’s results are anomalous because they do not fit in with the other two test’s results. Which are very close together.
Here is a graph showing the mean result of the experiment:
Conclusion
The above graphs give us a lot of information, one of the things the portray is the rapid decrease in mass form 5%. It starts off by gaining mass, but then it starts to decrease in mass from about 6%, forwards.
So, we can understand form this that after 6% sucrose solution, the direction of osmosis changes to being from the potato to the solution, when it started being from the solution to the potato. As the water particles pass out of the potato, it starts to lose mass.
Another fact that we find out from the graph is that at about 6%, the potato neither loses nor gains any mass, this means that the concentration of sucrose in the potato is most likely to be 6%. We know this because no osmosis is taking place.
When osmosis occurred in this case, the water molecules moved from the potato to the sucrose solution. The water molecules made up a large part of the mass of the potato. This is why the potato lost mass during osmosis, as it lost many water particles. This can be proved from the definition of osmosis: the movement of water molecules from an area of high concentration to an area of low concentration through a semi-permeable membrane.
When the concentration of the sucrose solution and the concentration inside the potato are equal there will be no mass change in the potato. Because one of them is not higher in concentration than the other, the water particles don’t need to pass to an area of low concentration through the semi-permeable membrane.
I predicted: the higher the concentration of the sucrose solution, the higher the rate of osmosis. Our investigation proved this to a certain extent. The prediction could’ve been modified to create a more accurate prediction: the higher the concentration of the sucrose solution, the larger the loss in mass in the potato.
Although the rate of osmosis was higher as the concentration increased, it was also a high rate of osmosis when the concentration was lower, but in the opposite direction.
although I was partially correct in my prediction, it would be easier to be more specific when thinking about the outcome.
Evaluation
The experiment could be greatly improved if it were to be done again. I would concentrate much more, as the smallest mistake could alter the results greatly. The method must be followed step-by-step, and this was not the case when I carried out the experiment, and this was due to lack of concentration.
One whole test gave us a set of anomalous results, this was also due to lack of concentration, we might have achieved these incorrect results, as a result of adding too much, or not adding enough of a certain variable.
But, in my investigation, there were three tests done, to ensure the accuracy of the mean result, this was a very good aspect of the investigation, and could’ve only been improved by doing more tests, which would be time wasting.
Our immersion time was also sufficient, because we were able to extract the necessary information from it with ease. It ensured that a wide range of results were obtained, and wasn’t too long, so the experiment was completed in an reasonable time at ease.
During our preliminary investigation, there was a slight problem with the potatoes, they kept sinking to the bottom of the test tube, posing a problem in their retrieval for the measuring of change of mass. This could have been avoided if the potatoes were smaller so they could float in the solution.
There are other investigations one could carry out, if the study were to be extended.
To find out about osmosis in plant roots and cells, one could do a detailed study over a period of time measuring the change in mass of a plant in earth. To do this one would need to take a cutting from a plant, with the roots and measure its mass at the start. Then one would plant this in a small pot of earth with a certain amount of water poured over it. To prevent evaporation, the plant would have to be covered. A specific environment would need to be maintained in order for the experiment to be successful. The amount of water would need to be decided on and kept the same throughout the experiment. After a fixed period of time, longer than in this investigation, one would take out the plant and measure the change in mass. This would tell one more about osmosis and how it works in plants, including the rate of osmosis in plants.
