Osmosis. Finding the water potential of potato tuber cells

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B 12MW                                                     Biology: Osmosis                                                      February 2008

Finding the water potential of potato tuber cells

“a cell is a city in disguise” – Copernicus

        Osmosis is the diffusion of water from an area of high water potential (Ψ  herein) to low water potential, through a semi permeable membrane. Using this movement of water you are able to determine the Ψ of a cell. And this is the basis of my coarse work as the aim is to:

“Use your knowledge of osmosis and the table provided, to design an investigation to determine the water potential of potato tuber cells.”

I have already told you the definition of osmosis my using this movement of water I will be able to determine the Ψ of the tuber cells. I will be able to work it out by placing potatoes pieces into solution of different molarity of water and measuring the % change in mass.

Choosing the molarity

In the experiment I will have to make my own solutions from one cock stock sucrose solution. I know form prior work, investigation and study that the water potential will be around 0.4M. So I have decided to use 6 different solutions that are on either side of this figure. Table 1 below shows which molarity’s I will be using.

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Table 1

Making the solution

        Of these 7 solutions I will have to make myself form the 1 mole stock sucrose solution. To make it I will need the following apparatus.

Apparatus

         

  • 1 mole stock sucrose solution
  • Distilled water (0Ψ)
  • 2 glass pipettes
  • 6x 250cm3 glass beaker
  • Homogeniser
  • Labels

Method

  1. Measure x amount of sucrose solution into homogeniser using glass pipette
  2. Measure x amount of distilled water into homogeniser using the other glass pipette
  3. Ensure that the pipettes are kept away from each ...

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Grammar good in the most part apart from one or two sentences do not read clearly. Punctuation is okay apart from in the listing where it is sloppy and rushed, spelling is good for the most part, apart from in one or two instances such as the misspelling of 'from' with 'form.'

Use of tables which is good although tables could be better presented, and the osmolarity of the different moles of solution does not need to be presented. Does not consider any confounding factors that could be present and does not measure them which could also improve the experiment e.g. age of the potato used, and time out of water. Graph too small and hard to read. Random link at the end of text and no reference to where it belongs. No evaluation or conclusion reached from the results, and no consideration of potential bias and things that could be improved in the experiment. Level of analysis basic for the level I would expect from this candidate which only base knowledge used and no complex scientific terms.

Basic essay. Introduction is good as it sets out the science behind the investigation and the theory. However, it does not submit a hypothesis which would have improved the investigation. Main body of the text basic, and no conclusion or evaluation providing an incomplete response to the question. Responses are clearly set out.