Investigate the effects of varying concentration of sucrose solutions on the amount of osmotic activity between the solution and a potato chip of a given size.

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Osmosis in Plant Cells

Aim 

The aim of this experiment is to investigate the effects of varying concentration of sucrose solutions on the amount of osmotic activity between the solution and a potato chip of a given size.

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 sucrose solution. This should give me a very varied set of results from which I hope to make a reasonable conclusion.  I must make sure that all of the controlled variables (listed below) are kept constant or else it would mean it would not be a fair test.  For instance, 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.  

Controlled Variables:

Controlling variables such as the ones below means that the experiment will be fair.

  • Temperature – for the purpose of my experiment I am going to do all my experiments at room temperature. I will make sure the temperature is constant by doing each experiment in the same room, and ensure that no other factors (such as open windows or strong lights) will change this.
  • Type of potato – the potato chips should all be cut from potatoes of similar size and weight, 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 osmosis has occurred and to what extent.
  • Volume of solution – the volume of the solution that the potato chips are kept in must be fair. The potato must also be totally covered in the solution and the amount of solution will be kept the same throughout.
  • Weighing equipment – the same balance should be used to weigh my potato chips. This is because the measurements may slightly vary between scales.
  • Number of tests – each potato tube in each different sucrose solution should be tested 3 times (a total of 15 tests) in order to obtain an average and more accurate results.

Prediction 

Osmosis can be defined as: ‘the movement of water molecules from an area of high water concentration to a low water concentration across a semi-permeable membrane’ (Collins dictionary 2001).

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 divided by a partially permeable membrane, the water will move from the area of high concentration to the area of low until both sides have reached an equilibrium (both sides are equal).

A Typical Example of Osmosis

Examples of osmosis can be seen in living cells too. 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.

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An Example of Osmosis in a Root Hair Cell

When a cell is placed in distilled water (high water concentration) water will move across the semi- permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. The cell is now referred to as turgid.  If a potato cell was placed in the same circumstances the cells would increase in length, volume and mass because of the effects of osmosis. If the same potato cells were placed in a solution with a low water concentration, then the effects would be the opposite – ...

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