Potato and Osmosis Investigation.

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Biology Coursework: Potato and Osmosis Investigation.

PLANNING: (P)

Some background Information: Water Potential and Living Plant Cells

Plant Cells in Pure Water: If plant cells are placed in pure water (a hypotonic solution) water will initially move into the cells. After a period of time the cells will become turgid. Turgor pressure is the pressure exerted against the cell wall by contents of the cell. At first most water movement is into the cell. As the turgor pressure increases water will begin to diffuse out of the cell at a greater rate, eventually equilibrium will be reached and water will enter and leave the cell at the same rate.

Free Energy and Water Potential: Free energy can be simply defined as the energy available (without temperature change) to do work. Chemical potential of a substance is the free energy per mole of that substance. Water potential is the chemical potential of water and is a measure of the energy available for reaction or movement (Bidwell 1974:59). Water potential is important when studying osmosis because it measures the ability of water to move, water always moves from areas of high potential to areas of low water potential.

The formula for calculating water potential is:

Water Potential = Osmotic Potential + Pressure Potential

Water Potential in Plant Cells: Water will move by osmosis into and out of cells due to differences in water potential between the cell and its surroundings. Remember that water always moves from areas of high potential to areas of low water potential.

Some Basic Principles:

  • Water always moves from high water potential to low water potential.
  • Water potential is a measure of the tendency of water to move from high free energy to lower free energy.
  • Distilled water in an open beaker has a water potential of 0(zero).
  • The addition of solute decreases water potential.
  • The addition of pressure increases water potential.
  • In cells, water moves by osmosis to areas where water potential is lower.
  • A hypertonic solution has lower water potential.
  • A hypotonic solution has higher water potential.

References: Bidwell, R.G.S. 1974. Plant Physiology. MacMillan Publ. Co. New York.643pp.

Weier, T. E., C.R. Stocking and M.G. Barbour.1974. Botany: An Introduction to Plant Biology. 5th ed. John Wiley & Sons. New York. 693pp.

What is Sucrose and what is it made up of?

Sucrose is made up of three elements which can be found in the periodic table, they are: Oxygen, Hydrogen and Carbon. But how many components are found with each element?

Oxygen contains: 11, 16 x 11 = 176g

Hydrogen has: 22, 1 x 22 =         22g

Carbon holds 12, 12 x 12 =       144g

                                      = 342g in 100dm³

That means there is 342g of sucrose in 1000cm³ of distilled water in a 1 molar solution, however we must divide this equation by ten so we get 34.2g in 100cm³ of water.

Preliminary Experiment: Before we begin our main experiment to this coursework, we conducted a preliminary experiment, this involved testing the rigidity of five separate ‘evenly cut’ pieces of potato chips from the same potato, we left the chips to infuse individually in five separate beakers, each with a different concentration (varying from 1 molar – 34.2g of sugar to 0 molar – 0g of sugar) we shall go down by 25 molar each time to get clear results, the whole procedure of the preliminary test was successful with the result of each potato chip being revealed as being different to the other. Below is a table of the results we found, plus a scatter diagram* to show how different sugar solute concentrations affect the rigidity of a potato chip.

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As we can see from pg 3, there are three isolated results at the top of the chart, (thus being: 1 Molar, 0.75 Molar and 0.5 Molar), I shall now rule two of these possible concentrations which I could use for my main experiment, I shall now not use these and concentrate on my main solutions and add a few more Molar concentrations varying from 0.5 Molar and 0 Molar to get a more accurate set of results, this should conclude what I have already acknowledged before, which was, as the general decline of concentration decreases then so shall the ...

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