Investigate the effects of varying concentration of certain solutions on the amount of osmosis in a potato chip of a given size.

Authors Avatar

Osmosis in Plant Cells

Plan:

Aim 

To investigate the effects of varying concentration of certain solutions on the amount of osmosis in a potato chip of a given size.

Prediction

 

A definition of osmosis is: ‘the movement of water molecules from an area of high water concentration to a low water concentration across a semi-permeable membrane’ (Oxford dictionary 2000).

In a high concentration of water the amount of solute (e.g. sugar) is low. These solutions are usually known as a dilute or weak solution. But in a low concentration of water the amount of solute (e.g. sugar) is high. These solutions are usually known as concentrated or strong solutions.  

When a weak solution and a strong solution are separated by a partially permeable membrane, the water will move from the area of high concentration to the area of low until both sides are equal. This is osmosis, and is shown in the diagram below.

An Example of Osmosis

Examples of osmosis can also be seen in living cells. Root hairs on plants take in water from the soil via osmosis. Water continuously moves along the cells of the root and up the xylem to the leaf. Water is moving to areas of lower water concentration all the time. This is shown in the diagram below.

Example of Osmosis in a Root Hair Cell

When a cell is placed in distilled water which is high water concentration water will move across the semi- permeable membrane into the cell which has lower water concentration by osmosis, making the cell swell in size. The cell is now known as turgid.  If a potato cell was placed in the same circumstances the cells would increase in length, volume and mass because of the osmotic effects. If the same potato cells were placed in a solution with a low water concentration, then the effects would be the opposite – water would move out of the cell into the area of lower concentration, the water. Thus, the potato chip will decrease in length, volume and mass. In more extreme cases, the cell membrane would break away from the cell wall and the cell is then known as plasmolysed.  

Osmosis in Plant Cells

The higher the concentration of water in the external solution, the higher the amount of water that enters the cell by osmosis.  The smaller the concentration of water in the external solution, the higher the amount of water that leaves the cell. However, there will be a point where the concentrations of water inside and outside the cells are equal. This is known as the isotonic point, and at this point there will be no change in the length, volume or mass of the potato, as the net movement of water will be zero and no osmosis will have occurred.

Using this information, I have come to the prediction that with a high concentration of sucrose in the water, the mass of the potato will decrease and the cells will become plasmolysed.  In a low concentration of sucrose the cells will become turgid.

Preliminary work

I have based my prediction on a prelimary experiment we did amongst our class, this experiment involved us placing potato chips into various concentrations of sucrose solution and observing the potato’s change in mass according to the solution they were placed in.

Carrying out a preliminary experiment helped me to decide how long to leave the potato chips in the sucrose solution.  In the preliminary I left them for 24hrs however I found this an insufficient time and this helped me to decide on leaving the potato chips for 2hrs in the final experiment.

Preliminary Experiment Results

Variables

In order to create a fair test, certain aspects of the experiment will have to be kept the same whilst one key variable is changed.  In my experiment, I have chosen to vary the concentration of the sugar solution. This should give me a very varied set of results from which I hope to make a good conclusion. I must make sure that all of the non-variables (listed below) are kept constant otherwise it would not be a fair test. For example, if one of the potato chips was slightly longer than the others, the surface area of the potato chip would be larger and therefore there would be more space for osmosis to occur.  

Join now!

Controlled-Variables:

  • Temperature – for the purpose of my experiment I am going to do all my experiments at room temperature.
  • Type of potato – the potato chips should all be cut from the same potato, using the same tool and without being washed or peeled, to ensure that my experiment is fair.  
  • Size of potato chips – the mass of the potato should be measured throughout the experiment, and should be measured in Grams. The potato chip will be measured before and after it is put into the solution. This will allow me to see whether ...

This is a preview of the whole essay