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

Investigating the Effect of Chilling on the Water Potential of Maris Piper Potatoes

Extracts from this document...


Investigating the Effect of Chilling on the Water Potential of Maris Piper Potatoes Osmosis is the net diffusion of water molecules from a region of high water potential to a region of lower water potential across a partially permeable membrane. Deionised water has the highest water potential with a value of 0 kPa. Solutions have a water potential below this and the greater the concentration of solutes the lower the water potential (Toole and Toole, 1995). Plant cells are bounded by a partially permeable plasma membrane, which is surrounded by a fully permeable cellulose cell wall. The cytoplasm and vacuole of a plant cell contains water with many solutes such as glucose, mineral ions and enzymes, all of which contribute to a low water potential. Soil water generally has a higher water potential than plant cells, which allows water to be absorbed down a diffusion gradient. Plant cells will continue to absorb water in this way until either the water potential is equal on both sides of the membrane or the plasma membrane is pushed right up against the cell wall. The cell wall is a fairly rigid structure composed largely of long parallel strands of cellulose, a polysaccharide of � glucose, held together by hydrogen bonds. This rigidity prevents the cell from bursting. The cell will become increasingly turgid until a point is reached where the pressure exerted by the cell wall on the membrane prevents further uptake of water by the cell. At this point the cell is said to be fully turgid. In whole plants it is the turgidity of their cells that helps hold them upright and spreads the leaves out to the sun so that they can photosynthesise efficiently (Jones and Jones 2000). Animal cells are not protected by a cell wall so if the fluid surrounding an animal cell has a higher water potential than the cytoplasm, the cell will continue to absorb water until either an equilibrium is reached or the plasma membrane bursts. ...read more.


This is the most difficult variable to control. * Time of soaking must be constant for all the potato pieces. The rate of osmosis will differ according to the water potential gradient between the potato core and the soaking solution. The greater the difference in water potential, the faster the rate of osmosis. As water diffuses across the plasma membrane from the higher water potential to the lower water potential the difference in water potential will decrease and the rate of osmosis will decrease until equilibrium is established on both sides of the membrane. There is not enough time to carry out pilot investigations to determine the length of time needed for equilibrium so the potato cores will be soaked overnight for 24 hours because this should be plenty of time for equilibrium to occur. * Species and age of potato (since being harvested) - different varieties of potato may have different water potentials so it is important to use all one variety. Many fruits and vegetables undergo changes after they have been harvested so by using potatoes that are bought at the same time from the same shop should reduce this variation but it is impossible to be sure that the potatoes were all picked at the same time or grown under the same conditions. Maris Piper potatoes have been chosen because they are described on the packaging as suitable for chipping. This means they must contain a fairly low reducing sugar content and any increase should therefore be easy to detect. * The volume of the salt solutions will be kept constant using a 25cm3 measuring cylinder. * The concentrations of the salt solution will be controlled by making careful dilutions and using only one batch of salt solution to reduce variation. * The mass of the potato will be measured using an electronic top pan balance, which weighs accurately to 0.01g. ...read more.


If the change in mass is measured, the effect of the residual liquid should not affect the results. Each core will be placed into a separate labelled test tube containing 10 cm3 of sodium chloride with a particular water potential. This will be repeated for each water potential. The potato cores will be left in the solutions for 24 hours. A water bath will be used to maintain a constant temperature. They will then be removed, dried systematically and reweighed. The mean % change in mass of potato will be calculated for each different salt solution. The mean % change in mass will be plotted on a graph against the water potential of the salt solution. Where the line crosses the x-axis will represent the approximate water potential of the potato tissue. This method has been chosen because it will measure any change in solute concentration i.e. both reducing and non-reducing sugars as well as other possible breakdown products such as amino acids. Additional work if there is time To check that any difference in water potential is due to an increase in reducing sugar content, a Benedict's test could be carried out. 10g of tissue from potato stored at 2oC and 24oC will be homogenised in a blender with a minimum volume of water. The mixture will then be filtered and 5cm3 of filtrate will be placed into a test tube. 2 cm3 of Benedict's solution will be added to each and the contents of the test tube boiled for 8 minutes in a heat block. The colour of the two solutions will then be compared. If a reducing sugar is present the colour will change from blue to green then yellow then orange then brick red. The final colour of the solution will depend on the concentration of reducing sugar in the potato tissue sample; the more the concentration of reducing sugar the greater the colour change (Larkcom and Miller, 2001). ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Molecules & 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 AS and A Level Molecules & Cells essays

  1. An experiment to find of the isotonic point of root vegetables cells in contents ...

    This occurred because a higher water potential was present in the sucrose solution than in the potato cylinder. Therefore the water molecules in the sucrose moved from a region of high water potential to a region of lower water potential through a partially permeable membrane into the potato cylinder.

  2. To find out how different concentrations of sucrose solution affect the incipient plasmolysis of ...

    For example the carrot at 0.3M increased in mass from 1.26g to 1.29g when added to the sucrose solution and this caused a percentage difference of 2.33%, furthermore at 0.7M the mass decreased from 1.27g to 1.22g after being added to the sucrose solution and therefore showed a negative percentage change of -3.94%.

  1. Investigating Osmosis.

    This is an example of dynamic equilibrium, and it applies to nearly everything that happens in the natural world. Diffusion occurs when a system is not at equilibrium. As an example, suppose you drop one drop of ink into a glass of water.


    POTENTIAL Is the ability of water to move and is represented by the Greek letter ? (pronounced as "Sigh"). It tells us which way water will move and how fast. Water moves into the symplast of plant cells by osmosis in response to differences in water potential, with water moving down gradient from areas of higher to lower potential.

  1. In this experiment we are going to be studying the affects of Osmosis in ...

    With the distilled water there will be more water in the solution than in the cell itself, so more water will pass through the cell membrane into the cells than pass through out of it. Therefore the cells will swell up, and the overall mass and size of the potato section will increase.

  2. An investigation into the effect of increasing the concentration of salt solutions on potato ...

    This is partially permeable. A plant cell in pure water will take in water by osmosis through its partially permeable cell membrane, to dilute the concentrated cell solution (cytoplasm). As the water goes in, the cytoplasm and vacuole will swell. However the plant cell has a very strong cell wall surrounding it.

  1. Experiment to investigate the water potential of potato tissues when immersed in various sucrose ...

    When immersed in pure water (which has a water potential of 0kPa, the highest value possible), the potato tissue will absorb a large amount of water from the external solution through osmotic means due to its relatively lower water potential.

  2. Does Lowering Storage Temperature Increase the Reducing Sugar Content of Potatoes?

    This enables samples of potatoes stored at a variety of temperatures to be tested and a close approximation of their reducing sugar content formed. This allows us to test to see whether samples of potatoes stored in a variety of relevant temperatures for a controlled time-scale will show the expected differing levels of reducing sugar.

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