Investigation of the effect of differing concentrations of sucrose solution on potato.

Plant cell in a less concentrated solution

In a less concentrated solution the cell will swell, however in a more concentrated solution the opposite occurs.  

Plant cell in a more concentrated solution

Therefore the hypothesis is justified.

Variables

My independent variable for this investigation is the concentration of sucrose solution.  This variable will be measured in Moles and I will range the variable from 0M to 2M

        My dependent variables are the mass of the potato piece in grams (to 2 decimal places) and the length of the potato piece in centimetres (to 2 decimal places.)

        My controlled variables are the total volume of solution that each potato piece is placed in, the time the potato pieces are left in each solution and the age and type of each potato piece.

Method

1. Collect the following apparatus- a 5mm diameter corer, Vernier callipers, a potato, a dissection board, test tubes, 2M sucrose solution, distilled water, a knife, a measuring cylinder and an electronic balance.
2. Set up the apparatus as shown in the diagram below

Diagram of apparatus

3. Cut out two pieces of potato using the corer
4. Measure the initial mass (in grams to 2dp) of each piece of potato and the initial length (in centimetres to 2dp.)  Record the initial weight and the initial mass on a table
5. Put 20 cm  of 2M sucrose solution into two of the test tubes
6. Add a potato piece into each test tube and leave overnight
7. Repeat steps 2 to 6 four times using a different concentration of sucrose solution each time.  Follow the table below to be able to make up the required solutions.

8. Remove the potato pieces and measure their final length and final mass and work out the percentage change in mass and length using the following two equations-

Percentage change in length

        Final length – initial length = Change in length

        Change in length

        Initial mass                X   100

Percentage change in mass

        Final mass – initial mass = Change in mass

        Change in mass

        Initial mass                X 100

9. Record all your results unto a table and plot your results onto a graph

Strategy for dealing with results

I will record my results unto 3 tables like the 3 three below-

I will plot two graphs using the following axes-

Fair test

To ensure a fair test and accurate results I will conduct two experiments for each different concentration and will calculate the average loss in weight and length.

        I will also leave all the potato pieces in each of their sucrose solutions for the same amount of time.

        Furthermore to ensure a fair test I will take all my pieces of potato from the same potato so that I can be sure that each potato piece is of the same type and age.

Safety

1. Take care with the corer as it has sharp edges and only use it on a dissection board
2. Take care in using glass ware such as the test tubes and measuring cylinder so as to not break them as splintered glass can be quite dangerous and painful of come into contact with
3. Keep stools and bags tucked under the desk
4. Wash hands immediately after experiment
5. Do not run

Justified prediction

I predict that the hypothesis that the potato will shrink in a higher concentrated solution but will expand in a les concentrated solution will be proved right in this experiment and I also predict that my graphs will follow the trends shown below.

The reason why the potato will shrink in a higher concentrated solution and will expand in a less concentrated solution is because of osmosis.  Water molecules move from cell to cell by osmosis.  Osmosis is when water molecules move from an area of high concentration of water molecules through a selectively permeable membrane to an area of low concentration of water molecules.  The water molecules move down a concentration gradient.

Plant cell in a less concentrated solution

In a less concentrated solution the cell will swell, however in a more concentrated solution the opposite occurs.  

Plant cell in a more concentrated solution

Results for Experiment

Table showing the change in mass

Table showing the change in length

Table showing the percentage change in mass and length

Interpretation

I can see from my results that my hypothesis that the potato will shrink in a higher concentrated solution but will expand in a les concentrated solution was true.

I can see from my graph and results that the hypothesis was proved correct and I can also see that my graphs follow the trend, which I predicted they would.

        The reason why my predictions and my hypothesis were proved correct is because of osmosis.  Water molecules move from cell to cell by osmosis.  Osmosis is when water molecules move from an area of high concentration of water molecules through a selectively permeable membrane to an area of low concentration of water molecules.  The water molecules move down a concentration gradient.

Plant cell in a less concentrated solution

In a less concentrated solution the cell will swell, however in a more concentrated solution the opposite occurs.  

Plant cell in a more concentrated solution

Evaluation

My results support the firm conclusion that the potato shrinks in a higher concentrated solution but expands in a less concentrated solution.  

        If I were to do the investigation again I would conduct three experiments for each concentration and calculate the average result.  I would also take a range of concentrations between 0M and 2M at 0.25M intervals rather than at 0.5M intervals.  Doing both these things would ensure that I would get even more accurate and precise results.