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Determining the water potential of potato cells by the weighing method
Anna Hill
Aim
To investigate the effects of osmosis in potato cells when placed in sucrose solution at various concentrations using the weighing method.
Background Information
Osmosis is the flow of water molecules by diffusion through a partially permeable membrane from areas of high water potential (low solute concentrations) to regions of low water potential (high solute concentrations).
Any substance dissolved in water is called a solute; a solvent is a liquid that is able to dissolve another substance, called a solute, to form a solution.
Water potential can be defined as the tendancy of water molecules to leave a solution by osmosis.
Water potential, w, is equal to the solute potential, s, plus the pressure potential,
p.
Therefore: w = s + p
Solute potential is the amount the solute molecules reduce the w, by reducing the number of water molecules per volume. ...
The greater the concentration of water molecules in a cell or solution, the higher its water potential. Pure water has the highest water potential – zero.
The more concentrated the solution, the lower and more negative its water potential. ...
Whether water enters the cell by osmosis will depend on the balance between external and internal solute and water potentials.
If the solutions on each side of the partially permeable membrane are of equal water or solute potential, then there will be no net movement of water molecules across the membrane. ...
A solution that contains more solute particles than another, and hence has a low water potential, is referred to as being hypertonic, whilst the less concentrated solution is hypotonic.
The water content of plants varies depending on environmental conditions. In land plants it plays a vital role in structural support and mineral transport and thus a lack of water may lead to wilting or possibly death.
Water is mainly absorbed through the roots, which are covered in specially adapted root hair cells, with large surface areas and thin cell walls to aid absorption by osmosis. The evaporation of water through stomata on plant leaves causes a transpiration stream, causing the water to be drawn up through xylem vessels.
Ions and sugars in the vacuole of plant cells lower the water potential, and water enters by osmosis.
Approximate Word count = 1848
Approximate Pages = 7.4
(250 words per page double spaced)
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