Biology

04. Determination of water potential by measuring changes in mass or length

  • 00:41 Why must you make sure all the potato skin is removed?
  • 01:15 Which method gives more precise measurements – measuring length to 1mm or mass to 0.01g?
  • 01:56 Why must the cylinders be left in the liquid for at least 45 minutes?
  • 02:00 Why do you blot the cylinders and not press too hard when blotting?
  • 02:28 Why is % change used?
  • 02:37 Which sodium chloride concentration gives no mean % change in mass or length?
  • 02:57 What is the ψ of the potato tissue?

  • vegetable e.g. potato

  • chopping board/ white tile

  • cork borers: sizes 3 and 4 are suitable

  • glass rod

  • ruler graduated in mm

  • mass balance (to 0.01g)

  • fine scalpel

  • fine forceps

  • 5 x boiling tubes

  • boiling tube rack

  • 50cm3 measuring cylinder

  • marker pen

  • deionised water

  • sodium chloride solutions (0.2, 0.4, 0.6, 0.8 mol dm-3)

Hazard Risk Control measure

Scalpel

Cuts to skin

Cut down and away from body onto a white tile or chopping board

Cork Borer

Cuts to skin

Push downwards onto a white tile or chopping board.