Osmosis In Potato Cells

Ben Zarй 9MK Biology Investigation - Osmosis in Potato Cells 9/7/04

Section 1 - Planning

Aim

What is the aim of your experiment? What do you want to find out?

The aim of this experiment is to investigate how potato tissue changes when placed in sucrose solution of different concentrations. Therefore, I want to find out if and how osmosis differs, when the concentration is changed.

Variables

What is the variable you are going to change in the experiment?

The input variable of this experiment (i.e. the variable to change) will be the concentration of sucrose solution present in the test tubes, which the potato samples will be placed into.

What is the variable you are going to measure in your experiment?

The output variable of this experiment (i.e. the variable to measure) will be the mass and length of the potato sample, before and after osmosis has occurred.

What are the other variables in your experiment? How can you keep them constant?

The variables to be controlled in this experiment are: the total amount of sucrose solution used, the size and shape of the test tubes used, the type of water used (in this case, it will always be distilled), the potato tuber used to collect potato samples (for one particular set of results), the length and circumference of the cork borer used the type of weighing machine used (i.e. how many decimal places it measures to).

Apparatus

What apparatus are you using? What is this piece of apparatus for? How does it work? Why did you choose it? How accurate is it?

* A potato tuber of a certain size and variety, to obtain all of the potato samples for one particular set of results.

* A cork borer to obtain samples of a certain circumference from the potato tuber, which can then be cut to a uniform length.

* Test tubes (6 for each set of results) to store the distilled water and sucrose solutions (of different ratios) in, after they have been measured out correctly. Then the potato samples can also be added to the test tubes.

* Labels will be stuck on to each of the six test tubes; to indicate what ratio the solution is in. This will make it easier to record results correctly and avoid mistakes.

* A scalpel will be needed to cut the samples, from the cork borer to a uniform length.

* A separate measuring cylinder will be used to measure the correct amounts of sucrose solution and distilled water (to avoid contamination). These measured amounts can then be added together, in a test tube.

* Sucrose solution (360g/dmÑ-) will be added in certain ratios to distilled water, inside test tubes.

* Distilled water will be added to sucrose solution, in certain ratios, inside test tubes.

* An electronic weighing machine (giving the mass to 2 d.p) will be used to measure the mass of the potato samples, before and after the experiment.

* A test tube rack would be used to hold each of the six test tubes.

Method

Write in simple steps a list of instructions you are going to follow in your practical. Make sure they are clear so other people can follow them. Explain why you are doing each step.

1. Firstly, the apparatus listed, above, would be gathered.

2. The six test tubes would then be placed into the test tube rack, securely, so that they are easily accessible but will not tip over or roll off the surface that will be worked on.

3. Next, the sucrose solution would be measured out six times in one of the measuring cylinders (each time, the appropriate amount of sucrose solution would be emptied into one of the test tubes and a label, with the number 1 - 6 would be placed on the appropriate test tube, indicating which solution is which).

4. The previous process would then be repeated with the distilled water, using the second measuring cylinder. The end result will be six test tubes, each labeled, with an equal total amount of solution. The solutions required for the experiment would now be prepared.

5. Next, the cork borer (with diameter 3mm) would be used to extract 6 samples of potato from the potato tuber.

6. The newly acquired potato samples would next be cut to an equal length.

7. With the potato samples and the solutions prepared, the actual part of the experiment that would need to be recorded could soon begin. So, after drawing two results tables (indicating the mass and length of a potato sample, before and after osmosis has occurred), the potato samples would be weighed on the electronic weighing machine and there mass would be recorded.

8. A potato sample would, next, be placed into one of the solutions for precisely one minute. It would then quickly be rinsed and dried and the new mass and length would be recorded. This should be repeated for each of the remaining potato samples, placing each one into a different solution.

9. This set of results (producing 12 individual results altogether) would be repeated 3 times, including the preliminary results, to give a more than sufficient amount of results.

Safety Precautions

How will you make sure the experiment is safe?

When conducting the experiment, no hazardous chemicals, which may cause harm to someone, are being used. However, two pieced of apparatus will need to be used with great care (the cork borer and the scalpel). They are both cutting instruments, which (as a result of this) are sharp and need to be handle with great care, to avoid accidents. The scalpels, when not in use, should have corks on the ends of them and there should be no need for the sharp part of either of these two instruments to come into contact with a person. Just as a final precaution, hands should be washed at the ends of a practical.

Fair Testing

How will you make sure this is a fair test and is not biased?

As was mentioned, only one input variable will be used (this being the concentration of the sucrose solution in the test tubes). This means that,