• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Weighing method of finding water potential

Extracts from this document...


Karl Byrne 137 Mrs. Knight Prediction I predict that the potato and carrot samples will lose mass proportionately to the concentration of the sucrose solution. This is because of water potential, and the fact that the higher the solute potential of the solution the lower its overall water potential. Results Change in Mass of Potato Tissue Placed in Varying Concentrations of Sucrose Solution Molarity/mol dm-3 of sucrose solution Weight of potatoes Before (In Grams) Weight of Potatoes After (In Grams) Difference Between the two masses Percentage Change in Mass 0.0 0.52 0.80 +0.28 +53.84 0.1 0.68 0.67 -0.01 -1.47 0.2 0.70 0.64 -0.06 -8.57 0.3 0.61 0.46 -0.15 -24.59 0.4 0.61 0.47 -0.14 -22.95 0.5 0.52 0.42 -0.10 -19.23 Change in Mass of Potato Tissue Placed in Varying Concentrations of Sucrose Solution(Class Averages) Molarity Of Solution Percentage change in Mass 0.0 +18.47 0.1 +3.33 0.2 +0.08 0.3 -11.79 0.4 -21.28 0.5 -22.45 Change in Mass of Carrot Tissue Placed in Varying Concentrations of Sucrose Solution Molarity Of Solution Percentage change in Mass 0.0 +15.40 0.2 +12.68 0.4 +5.43 0.6 -4.07 0.8 -4.85 Interpretation Water can move very easily into and out of a cell by a process called osmosis. This process involves the movement of water from a high concentration to a low concentration across a semi-permeable membrane. In the above example water can be seen moving from the right hand side where there are more water molecules to the left hand side which has fewer water molecules. ...read more.


This is because the carrot contains more soluble sugar, such as monosaccharides or disaccharides, which are reducing sugars. We know that it is a reducing sugar, due to the fact when Benedicts is added to it and brought to the boil; a yellow/brown precipitate is form, which shows presence of reducing sugar (e.g. monosaccharides). This means that the carrot has a relatively lower water concentration than the potato. This is because carrots naturally have more soluble sugars and this affects the water potential. Because water molecules have kinetic energy, they are constantly moving around in gaseous or liquid form, moving randomly from one place or another. The sucrose in the solution lowers the total kinetic energy of the free diffusing water molecules will decrease. This means that the water molecules are not able to move around freely and their tendency to diffuse out of a solution will decrease. However potatoes do not contain as much soluble sugar as the carrot does, it mainly has insoluble macromolecules. It contains starch molecules. Starch is stored very compactly as coils and is very easily stored. It is a very effective store of energy as it can be easily hydrolyzed to give glucose and is made up of thousands of glucose molecules linked up together by hydrogen bonds in a compact spiral or coil shape. It is used as a storage polymer of glucose in plants. It is a non- reducing sugar we know this because when it is boiled with HCl and Benedicts, it again has a Yellow / Brown precipitate. ...read more.


To keep the test fair, we have to cut all the potato discs the same size, surface area etc. But putting this theory into action wasn't easy and mistakes were made. But this was down to Human Error. When it came to weighing the potato tissue after the experiment, we dabbed the discs with a paper towel. However, in doing this we could have removed water that was not excess, and altered our results. Another way of improving the results would have been to leave the experiment running longer, this would have enabled me to find the saturation point (when the potato can no longer take in any more water) and dehydration point (when the potato cannot lose any more water) and therefore get a more accurate result. Finally, I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope e.g. incipient plasmolysis. An example of this is immersing onion cells in a range of sucrose solutions of different molarities and watch them till at least 50% of the cells have been plasolytised. Incipient plasmolysis is the point when plasmolysis is about to happen and at this point the pressure potential is equal to zero so the water potential and the solute potential are equal and the water potential of both the cell and the surrounding solution are the same.. At incipient plasmolysis the protoplast has just ceased to exert any pressure against the cell wall, so becomes flaccid. With incipient plasmolysis I would be able to see the cells in greater detail and draw some more observational results. ...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. Water potential of potato tuber cells - the weighing method.

    Using the same cork bore every time to ensure they are all the same width and this ensures a fair test. 4) Then measure each cylinder and check that they are all 12mm in length. Yet again using the same ruler just to ensure a fair test.

  2. Investigation to compare the water potential between potato chips and carrot chips.

    I set the apparatus as shown in the following diagram: Once this is done I will follow a similar method to the one which I will carry out when using both carrots and potatoes. The quick method I carried out was: Make solutions - different concentrations, put solutions into test

  1. Osmotic pressure

    for it to take place - therefore it is an example of passive transport as it does not require energy. Water Potential Water molecules move randomly, and when water is enclosed by a membrane, living or artificial, some of the moving water molecules will hit the membrane, exerting pressure on it.

  2. Osmosis is defined as 'the movement of water molecules from an area of high ...

    Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow. As the potato is a plant cell, it contains a vacuole and a cytoplasm. The cell membrane is also partially permeable i.e.

  1. Determination of the water potential of root/tuber cells by the weighing method.

    the boiling tube with forceps, make a note of which tube it is in and record the mass of the filter paper on its own. Calculate the initial mass of each cylinder once you have transferred them all to the tubes.

  2. Free energy and water potential.

    of the plasma membrane. This is due to the relatively small size of water molecules. Many hypotheses suggest that water penetrates through the phospholipid bilayer through other ways. It has been stated that water molecules may move through temporary faults that are created by flexing and bending movements of fluid hydrocarbon chains of phospholipids.

  1. Water potential is a measure of the free kinetic energy of water in a ...

    Changes in length and weight will occur if the external solution has a higher or lower water potential .If there is no change in the length and mass of the samples, then that means that the external solution has got the same water potential as the sample.

  2. Investigating the cellular water potential of potato cells.

    Where there is no loss in mass or gain in mass in the potato samples is where the water potential of the solution and potato cells are in equilibrium. This water potential is the water potential of the potato cells.

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