Osmosis in Potatoes.

Osmosis in Potatoes

Osmosis is a special type of diffusion where water moves across a semi permeable membrane from an area of low solute concentrating to an area of high solute concentrating. Osmosis is an important in plant cells as it makes the cell turgid. Turgidity is when no more water can enter the cell and therefore helps to keep the plant firm and upright.

Variables:

Some parts of the experiment will have to be kept the same while one key variable is changed. Some of the variables I am going to control are:

Time left in solution – If the chips were left longer in the solution than others, more time would be allowed for osmosis to occur.

Surface area of potato chip – If the surface areas are larger on some chips than others there would be larger and there would therefore be more space for osmosis to happen.

I have chosen to change the concentration of the sugar solution. If any of the non-variables aren’t kept constant it would mean it would not be a fair test.

Apparatus:

Test Tube Rack

We used this to put the test tubes in so they wouldn’t fall over.

5 Test Tubes

– We used these in order to put our chips and the sucrose solution in.

1 Measuring Cylinder

We used this in order to measure accurately the amount of Sucrose Solution being put into the test tubes.

Chipper

This was used in order to cut the chips to the same size so that all the chips would have the same surface area

5 Bungs

We used these to prevent evaporation.

Method:

First we must peel the potato, as leaving the skin on during the experiment will effect the rate of osmosis on the chip.
After peeling the potato carefully put it in the chipper. Doing this will ...

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We used this in order to measure accurately the amount of Sucrose Solution being put into the test tubes.

Chipper

This was used in order to cut the chips to the same size so that all the chips would have the same surface area

5 Bungs

We used these to prevent evaporation.

Method:

First we must peel the potato, as leaving the skin on during the experiment will effect the rate of osmosis on the chip.
After peeling the potato carefully put it in the chipper. Doing this will help to control the variable of length and width and will give each chip an equal surface area.
Measure each chip to 3cm using a ruler. This must be done carefully as a change in the surface area may allow more or less osmosis to occur.
Get the test tube and the measuring cylinder and pour in 40ml of undiluted sucrose solution. Hold it eye level to see if its exact. Then get 3 of the 3cm chips, carefully place them into the test tube and put a bung on it. (Using the bung makes sure that evaporation doesn’t occur).
We then measured out different concentrations of sugar solutions, and diluted several of them with water (H20). 0% Sugar solution, 25%, 50%, 75% and 100% sugar solution. We measured each amount of liquid with a measuring cylinder and used a simple total (40ml) so we could easily work out the percentage of liquid.
We then placed three of the potato chips into each of the test tubes and put a bung on top.
We left the chips in the concentration for 24 hours for the osmosis to occur.
The next day we emptied the test tubes in a sieve and measured each chip from each solution.

Prediction:

I believe that the more Sucrose solution present in the test tube the smaller the chip will be. This is because water diffuses from the chip through the semi permeable membrane and into the sucrose solution because it has a lower concentration of water. So when loads of the water has diffused from the chip it will shrink and will no longer be turgid instead it will become flaccid. Flaccid is the exact opposite of "turgid", instead of the cell-becoming firm it becomes soft and limp.

Aim

The aim of this experiment is to investigate the movement of water into and out of plant cells by osmosis.

Science:

A previous experiment I did on Osmosis was also done using potato chips, though these were left for 48 hours and done using dilutions of 0%, 50% and 100%.

Here are my results:

These results were not very reliable as only one chip was used per solution so there is more chance for anomalies to occur.

Obtaining Evidence:

I did the experiment three times, in each solution, and then took an average in order to have a fairer reading. I also did at least 5 types of different concentrations, to have enough results and to see if my prediction was correct.

From my results I can conclude that as the concentration of sugar solution increases, the mass of the potato chip decreases. This is because water diffuses from the chip through the semi permeable membrane and into the sucrose solution because it has a lower concentration of water. There are no anomalies in my results though there wasn’t as big a change in chip lengths as I would have expected to see in the experiment with most only decreasing 0.04cm.

Analysis:

As you can see the lower the percentage of Sucrose Solution the bigger the average chip length, and the higher the concentration the smaller the chip length.

This is because the water molecules pass from a high concentration, like in the water, to a low concentration, in the potato chip.

Take a look at the graph

At point A (0% Concentration of Sucrose Solution), the cell can not increase any further in size. This is because the cell is fully turgid and no more water can enter it.

At point B (100% Concentration of Sucrose Solution), the cell is not decreasing any further in size. This is because the cell is fully plasmolysed and no more water can leave the cell. (Plasmolysed is when a plant cell loses water and the vacuole shrinks. The cytoplasm and membrane shrink away from the cell wall. This is a plasmolysed cell.)

Evaluation:

The results we got from the experiment were reliable and fitted a clear pattern. Though I believe if we were to have done the experiment again with more chips and a bigger variety of dilutions like 10%, 20%, 30%, 40% etc. then we could have got more exact results. Also when controlling variables if we had controlled the temperature then the experiment would have less chance of mistakes and anomalies, as having a different temperature in one test tube than another will change the rate of osmosis. When measuring the chips we could have got more exact results by using a Vernier Calliper as this measures to the closest 0.1mm and would therefore give a more accurate measurement giving us more exact results.