Investigation into how the concentration of sugar solution affects osmosis in a potato.

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Investigation into how the concentration of sugar solution affects osmosis in a potato

Planning

Introduction

Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. The potato I will be using will allow water molecules to advance into it by tiny holes in the membrane; the sugar will be too large to fit through. Osmosis is the movement of water molecules from a region of high concentration to a region of low concentration through a partially permeable membrane, this means that if the water concentration is high in the potato tissue then the water will pass out of the potato back into the solution. If the water concentration is low in the potato tissue then the water molecules will pass from the solution back into the potato resulting in accumulation of the mass. Therefore, If there is very little different in the two water concentrations, there shouldn’t be a big change in mass.

During osmosis the cell will change like this:

Diagram 1.        Diagram 2.        Diagram 3.

                                                 

These could be potato cells. In diagram 3 which is filled with water (dots) is known as turgid. This cell can take in no more water.

If these potato cells were placed in a solution with a low water concentration, like diagram 1 then the opposite would happen. Water would move out of the cell into the solution.

In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass.

During our experiment the potato will need some kind of element to survive. The potato will use water. Using this source the potato can carry on working until it has too much water in it or too little water in it. If the potato is lacking water the water particles will move from the solution to the potato via osmosis until both sides become equal, making no more reactions.

 

The variables involved in our experiment are:

  • Independent – things that you change
  • Dependent – things that you measure
  • Fixed – things that stay the same

The Independent variable that I will change is the concentrations of the solutions. I will use a varied range of molarities to help me investigate osmosis in the potato.

The Dependent variable that we will measure is the mass change in the potato before and after it has been in the solutions. We will compare the first measurement to the measurement after the potato has been in the solution to see how the potato how changed in mass; how much osmosis has happened.

The fixed variable's that I will use to keep the amount of solution the same in each different experiment. I will measure using a measuring cylinder. I will also keep the same amount of potato the same weight, size and shape every time. I will weigh the potato using digital scales correct to 2 decimal places. I will use the same potato every time; this is because different potatoes could have different water amount within them.

Aim

My aim for this experiment is to find the results of a potato tissue's mass difference, when placed in different concentrations of sugar solutions.

Prediction

  1. For the distilled water I think that the weight of the potato tissue will gain in mass. I anticipate the mass will increase, as I believe the concentration of cytoplasm in potato tissue is more concentrated resulting in water being transferred by osmosis into the potato. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid; taking in all the water it can possibly take in.
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  1. For the 0.2 molar sucrose solution I think the result will be similar to the distilled water. The concentration gradients are very similar therefore the mass won’t vary a large amount. I predict that the weight of the potato will stay above 1gram producing a rise in mass.

  1. I think the 0.4 molar solution will decrease in weight by a fractional quantity, as the concentration gradients between the 0.4 molar solution and the 0.2 molar solution are similar. This is why I predict the mass will only be decreases by a small amount.

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