To investigate the effect of varying concentration of different sugar solutions on the amount of osmotic activity occurring between the solution and the potato chip

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Aim: To investigate the effect of varying concentration of different sugar solutions on the amount of osmotic activity occurring between the solution and the potato chip.

Prediction

  • I predict that the potato chips will lose weight in the concentration levels of over 0.4M sugar solution and gain weight at concentrations of 0 and 0.2 molar solutions.
  • I further predict that the weight loss will be around 1/3rd of the original mass at 1M concentration.
  • The weight loss will decrease according to a third order polynomial when plotted on a graph. In distilled water there will be a weight gain of around 15%.

Justification of prediction

Osmosis is defined as the movement of water across a partially-permeable membrane from a place of higher concentration to a place of lower concentration until a state of equilibrium between the two is reached. This movement must take place across a partially permeable membrane such as a cell wall which allows small molecules such as water to pass through but not larger ones such as sucrose.

In my experiment, this movement will continue to occur until a state of equilibrium between the sucrose solution and the vacuole of the potato cell has been reached. Since the potato will have some amount of sucrose in its vacuoles, there will be a higher concentration of water in the low molar sucrose solutions and in the distilled water than in the potato vacuoles. This means water will move down a water potential gradient from the solution into the potato vacuoles and thus potato chip will gain weight.

At the higher molar concentrations of sucrose solution there will be a lower concentration of water molecules in the sucrose solution than in the potato vacuoles. Therefore, osmosis will occur down a water potential gradient from the potato chip into the sucrose solution and the potato chip will lose weight.

In this diagram of osmosis the water is moving from an area of high concentration to an area of low concentration. If the potato were the right hand side and the sugar solution was the left hand side the potato would be losing its water molecules into the sugar solution and therefore decreasing in mass.

This is the knowledge which I used to come up with my prediction. If I immersed the potato chip in distilled water the potato would gain mass for the same reason; there is a higher concentration of water in distilled water than potato vacuoles, osmosis will occur and water will enter the vacuole of the potato cells from the distilled water.

During my preliminary experiment this prediction was confirmed which further reinforces the accuracy of my prediction.

Say more about preliminary test backing up prediction

Background information

This diagram gives guide to what happens to the cells when osmosis occurs between them and another medium.

A turgid cell is one full of water, this will happen to the cells immersed in concentrations with lower sucrose levels than the potato cells. The potato chip will gain weight

A normal cell is a cell where no osmosis occurs (isotonic), this will happen when the sucrose solution is the same molar concentration as the potato cells. There is no weight change in the potato.

A plasmolysed cell is one where water has moved out from the cell and the cell has lost weight. The cell is flaccid.

Variables which may affect the outcome of my experiment

In order to make this experiment a fair test I must ensure that the only variable changing is the molar concentration of sucrose in which the potato chips will be immersed. Other factors which could affect my results are listed below:

  • Temperature – the higher the temperature the more energy the molecules will have and therefore they will move faster and have more collisions thus meaning osmosis will occur faster. Therefore I will check the temperature every 10 minutes to make sure it is the same throughout.
  • Surface area – The greater the surface area of the potato the more of the potato chip will be exposed to the solution and therefore more osmosis can occur. By cutting each potato chip to 3cm and using the same size cork borer throughout the surface area should remain very similar throughout.
  • Duration of the experiment – The longer the potato chips have in the solution the more time osmosis has to occur. I will make sure each piece of potato has the same amount of time in the solution.
  • Volume of solution – If there is a higher volume of solution the less of a difference the water molecules given or received by the potato chip will make. Therefore I will ensure each volume is the same.
  • Mass of potato chip – If the potato chip is small the ratio of surface area to volume will be greater than if the potato chip is large. This will make the percentage weight change greater for smaller pieces than larger pieces. Therefore I will use the same size of potato chip for each solution.
  • Top-pan balance – some top-pan balances may be different to others. To reduce the chances of a balance induced error I will use the same top-pan balance throughout the experiment.
  • Potato sucrose concentration – Different potatoes have different levels of sucrose in their vacuoles, this would control how rapidly osmosis occurs. To try and keep the sucrose levels of the potato equal I will use the same potato throughout the experiment.
  • All the samples were cut so they had no skin on them. If they had skin it would mean the surface area for osmosis would be reduced.
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Preliminary Method and how it informs the rest of my plan

In order to find out the best size of potato chip and optimum amount of time to leave the potato in the solutions I carried out a preliminary test using different sizes of potato chips and varying the amount of time I left them in.

Preliminary results go here

In the preliminary experiment I found out that the longer I left the potato chips in the solution, the greater the weight change and therefore the more accurate my results. I decided that one hour was the maximum amount of ...

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