Water Potential

• Calibration curves are graphs used to determine an unknown concentration of a sample by comparing it to a set of standard samples with known concentrations
• Dilution series can be used to create a set of samples with known concentrations
• A calibration curve can be used to determine an unknown water potential in a potato sample
• Water potential is the tendency of water to diffuse from one area to another
• Water molecules move from areas of high water potential to areas of low water potential by osmosis
• Water potential is determined by the concentration of solutes
• The movement of water in and out of cells is related to the relative concentration of solutes on either side of the cell membrane
• The point where the line of best fit crosses the x-axis (zero change in mass) indicates the point where the solution is isotonic
• Isotonic point is when the water potential of the sucrose solution is the same as the water potential of the potato tissue, resulting in no net movement of water in or out of the potato
• Potato chips in lower concentrations of glucose solution will increase in mass
• Potato chips in higher concentrations of glucose solution will decrease in mass
• In dilute glucose solutions, water moves passively via osmosis to the area of lower water potential (the potato), causing the potato to increase in mass
• In concentrated glucose solutions, water moves out of the potato, resulting in the potato decreasing in mass
• Describe an experiment that you could do to investigate whether the mangrove root cells have a lower water potential than sea water. You are given:

  • a piece of fresh mangrove root

  • sea water

  • access to laboratory equipment.

  1. Record mass before and after;
  2. Place in sea water for (specified/equal) time;
  3. Blot dry with tissue;
  4. Increase in mass shows water has been absorbed by osmosis (lower water potential);
• High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid. Explain how.

  1. Higher salt results in lower water potential of tissue fluid;
  2. Higher salt results in higher blood pressure/volume;
  3. So more fluid forced out of capillary;