Osmosis in Potato Course Work

What affect does concentration of solution have on potato tissue?

In my preliminary investigation, I will be controlling the following variables:

* length of potato cylinder;

* amount of solution / water;

* type of potato;

* size of potato;

* temperature of water;

* same ruler / person.

Changing the concentration of solution:

Using three glass test tubes, I will set up the following configuration:

* Test tube 1 - Distilled water;

* Test tube 2 - 5% salt solution;

* Test tube 3 - 10% salt solution.

All quantities will be made the same and accurately measured to ensure a fair test.

I will accurately cut three pieces of potato chip (40mm / 4cm), each one the same length. Each chip will then be inserted into each test tube simultaneously. I will then leave them in the test-tube for twenty minutes, take each out simultaneously and then record the difference in length for each chip.

After conducting my preliminary experiment, I have recorded the following results:

To improve the reliability / accuracy of my preliminary investigation, I could make the following changes:

* not using the same cylinder to measure out the different water solutions;

* calculating the mass change in the potato chip, by measuring both length and width of the potato chip;

* calculating a value.

I am investigating what effect changing the external concentration of a solution has on potato tissue. I have carried out a preliminary result and will now repeat the experiment with an improved method after reviewing the flaws discovered in my preliminary experiment.

There are several variables I can control in order to get a different outcome to my experiment:

* temperature of the atmosphere in which the investigation takes place;

* surface on which the investigation takes place;

* length of time in which the chip is submerged in the solution;

* position of potato chip;

* size of potato chip;

* amount of solution;

* concentration of solution.

I will change the concentration of the solution in more regular intervals compared to that of the preliminary experiment - 0%, 2%, 4%, 6%, 8% and 10%. Last time, I carried out the experiment varying intervals of 0%, 5% and 10% salt concentration. Decreasing this range will result in more accurate results, with more to analyse and therefore enable me to gather a greater idea of what is going on in this investigation. I will control the temperature of the atmosphere in which I conduct my investigation by carrying it out in the same location each time. I will control the surface I am working on and keep the chip size consistent by accurately cutting the chip. I will try to ensure that the position of the chip within the solution remains consistent so that my investigation is accurate and gets the best results possible.

For my investigation, I will be using:

* a balance to two decimal places;

* six beakers;

* a razor, and;

* a ruler, to accurately cut the potato.

I predict that the mass of the potato will decrease because water will move from high to low area of concentration. For the potato chip in 0% salt solution - i.e. distilled water, the mass will increase as the water moves the opposite way, into the potato chip.

After having drawn by graph, I can use it to analyse my results collected from the investigation and conclude an evaluation.

My graph shows that as the concentration of salt increases, the mass of the potato decreases.

For example, the average % change at 0% was +4.66.

However, at 10%, the average change was -22.6.

Therefore a 27.26% difference

The reason for this is because of the process of osmosis.

Osmosis is the diffusion of water from an area of high concentration to an area of low concentration, through a ppm (partially permeable membrane).

In my investigation, this particular diffusion was the diffusion of water from an area of high concentration (inside the potato chip) to an area of low concentration (into the volume of salt water in the beaker). The partially permeable membrane in this instance is the cell membrane round each cell.

I was able to predict this using my scientific knowledge. My prediction was correct. I can clearly see from my results that the mass of potato has decreased because the water has moved out in all the salt solutions, whereas in distilled water, the water has moved the other way, into the cell, where the mass increased.

The method I used for my investigation was better than the method for my preliminary test. This time I accurately cut and carefully measured potato chips.

I weighed the chips before and after to get a far more accurate result based up on change in mass rather than change in length (as I had noticed that the diameter changed in the preliminary experiment.

One major flaw in my investigation is that results may be inaccurate or anomalous due to human error. The degree of concentration and organisation whilst conducting the practical could result in chips getting mixed up before and after weighing.

Maybe doing one chip at a time could solve this.

Most of my results match my line of best fit. There are some points that are a little far away from my line of best fit, for example, the results recorded for 10% salt solution. A difference greater than 25% is unreliable because there could not have realistically been that much water movement take place.