• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17

Investigate the water potential of a potato tuber.

Extracts from this document...

Introduction

My aim in this investigation is investigate the water potential of a potato tuber. This investigation needs a lot of planning and prediction with the use of scientific knowledge involving preliminary experiments, which will guide me for the main experiment to be successful and for it to produce concise and accurate results to prove the hypothesis, explained in the prediction. The main theory used in this experiment is the theory of osmosis, which is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration (http://www.purchon.com/biology/osmosis.htm). Osmosis controls the exchange of molecules through the semi permeable membrane. It allows small molecules like oxygen, water, carbon dioxide, ammonia, glucose, amino acids, etc. to pass through. Cell membranes will not allow larger molecules like sucrose, starch, protein, etc. to pass through. If the solution surrounding the cell has a higher water concentration than the cell (a very dilute solution) the cell will gain water by osmosis and vice versa. A key feature of osmosis is that only water molecules move across the membrane to bring the two solutions to and equilibrium. This equilibrium is reached when the water potential in one region is the same as the other region. Water potential is the chemical potential (i.e. free energy per mole) of water in plants. Water moves within plants from regions of high water potential to regions of lower water potential, in other word down a water potential gradient. It is this tendency to move which is called water potential (Cambridge Advanced Sciences Biology 1, Mary Jones et al, 2000). It is affected by two factors, which are solute potential (?s) and pressure potential (?p). The solute potential is a measure of the number of dissolved particles in water, for example the amount of dissolved sugar or salt. In pure water the solute potential is zero because there are no solute molecules at all. ...read more.

Middle

error because it will allow osmosis to occur more or less so this will affect the water potential in those few cells (independent variable) I will leave the all the tubers in for sufficient time, that is, 24 hours and will note the exact of putting the cylinders in solution and taking them out. (Independent variable) Before completing the actual experiment I did a preliminary experiment similar to what my actual experiment be like but instead I chose to use an onion. In this experiment the aim was to observe the process of plasmolysis and to record the plasmolysed state in the epidermal cells of the onion. If a plant cell is in contact with a hyper tonic solution, that is a solution that has a higher solute concentration than the cell contents, water leaves the cell by osmosis via the cell membrane. Water is lost first from the cytoplasm and then the sap vacuole through the tonoplast. The protoplast the living part of the cell (cytoplasm and the nucleus) shrinks and eventually pulls away form the cell wall - this process is called plasmolysis, and the cell is said to be plasmolysed. In the experiment I used 6 different concentrations of sucrose solution varying from 0.1 molar to 1.0 molar shown in the table below: Ratio of water Ratio of sucrose Molarity of sucrose solution 8 2 0 7 3 0.3 6 4 0.4 3 7 0.7 2 8 0.8 0 10 1.0 I removed a strip of epidermis from the inner surface of one of the fleshy storage leaves of the onion bulb. First slitting it with a scalpel, and tearing back the single layer of cells with forceps can remove the epidermis. I cut up this epidermis into seven 5 x 5 mm (approximately) pieces. I put each of these in the different concentrations and waited for about roughly 20 minutes. ...read more.

Conclusion

This shows that I had carried out the experiment fairly and accurately, although they are not all exactly fitted on the line of best fit, this small difference may be due to many reasons, as it affected all the different concentration From this graph it is possible to work out the point at which it has cut the x-axis accurately using the equation of the line. At this point incipient plasmolysis occurs, the pressure potential is zero. From the use of excel I have drawn a trend line which is more accurate then the one that I have done previously by hand (-74.429 being the gradient and 27.381 being the y-intercept following the rules of mathematic where y = mx +c). If it is not accurate it is not possible to see where the line cuts the x - axis. Below I have worked out this point: The equation of the line is Y = -74.429x + 27.381 At this point y = 0 ? 0 = -74.429x + 27.381 -27.381 = -74.429x x = -27.381/-74.429 = 0.367880799 This is the molarity of sucrose solution at which point incipient plasmolysis occurs. This is a very accurate number because it is up to 9 decimal places, which is not necessary but is very accurate. On my and drawn graph you can clearly see that this same point is at 0. 38, which is not accurately because the line of best fit has been drawn approximately. As we found out from the experiment even small changes in concentration can have an effect in the percentage change in mass. Here is a table of solute potentials of sucrose solutions (at 20?C). This will help me work out the water potential Concentration of sucrose solution (Molarity) Solute potential Kpa 0.05 -130 0.10 -260 0.15 -410 0.20 -540 0.25 -680 0.30 -820 0.35 -970 0.40 -1120 0.45 -1280 0.50 -1450 0.55 -1620 0.60 -1800 0.65 -1980 0.70 -2180 0.75 -2370 0.80 -2580 0.85 -2790 0.90 -3010 0.95 -3250 1. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Life Processes & Cells section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Life Processes & Cells essays

  1. Marked by a teacher

    How does the concentration of a sucrose solution affect the rate of Osmosis in ...

    5 star(s)

    at the end, but is still in a curve rather than a horizontal line. This implies that it could lose some more water before it reached the point where it was unable to allow any more water to leave the cells.

  2. Marked by a teacher

    To determine the water potential of a potato tuber cell using varying salt solution.

    5 star(s)

    Pressure potentials are caused by resistance of the tissues to water flow7. To calculate water potential this formula is used: Water potential ? = solute potential ?s + pressure potential ?p The differences in pressure potential of potato cells placed in different concentrations of salt solution, will cause the cell to react in different ways.

  1. Marked by a teacher

    An experiment to investigate how the effect of varying concentrations of salt solutions play ...

    4 star(s)

    > I should keep all my things out of the way such as my, bag, blazer, and stool should be stored underneath the desk so I don't trip or fall. > I shouldn't sit down when carrying out the experiment.

  2. Marked by a teacher

    To investigate how varying the concentration of sucrose solutions affects the rate of osmosis ...

    3 star(s)

    Unless all the potato cylinders are completely immersed in the solutions, the rate and amount of osmosis will not be equal and this would make my investigation an unfair one. 8. I used cylinders from the same potato to ensure that they were of the same structure and concentration to

  1. Aim To determine the water potential of a potato tuber cell

    This is because osmosis moves from higher water potential to lower water potential. (Fig 2) However, if a potato chip is placed into a solution of 0 molar concentrations such as distilled water, it should gain weight and become more turgid.

  2. An Investigation to determine the Water potential of Potato cells.

    Therefore the water potential of the potato cells can be found by placing the potato tissue in an external solution, which produces no change in mass or length in the tissue. The osmotic potential can be found by balancing the tissue with an external solution, which produces incipient plasmolysis.

  1. To determine concentration of cell sap in potato tuber cells.

    Method- ~ Take six ready cut strips of potato tuber, weigh them and record their masses ~ Place each one in a test tube containing distilled water/sucrose solution and leave for 24 hours ~ Take them out and blot them on filter paper ~ Weigh them and record their masses

  2. The endeavour of this investigation is to ascertain if there is any effect of ...

    Therefore at 0M and 0.2M I expect the: Potato potential < solution potential At 0.4M I expect a different effect in which the both the solution potential and potato potential are equal, resulting in no change in mass. This is called the equilibrium point and I believe it is at

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work