Laboratory Notes for BIO 1003

© 30 August 1999, John H. Wahlert & Mary Jean Holland

DIFFUSION AND OSMOSIS

Materials

Demonstrations on instructor’s bench:
  • Demonstration 1. Materials: 250 ml graduated cylinder filled with tap water; potassium permanganate crystals, metal scoop for introducing them into cylinder.

  • Demonstration 2: Materials: plastic thistle tube; 600 ml beaker of tap water; stand with clamp to hold inverted thistle tube; frog intesting, rehydrated (semipermeable membrane); rubber band; concentrated sugar solution (about 60%) colored with methylene blue for visibility. Setup: Fill bowl of thistle tube with concentrated solution, cover with frog intestine and affix with rubber band; invert thistle tube; hold with clamps on stand; partially submerge bowl of tub in tap water; mark stem at initial level of colored sugar solution; record change over time.
Student equipment:
  • 6 balances (weigh up to 200.0 g), 1 at ech station
  • microscopes
Glassware (setup at each of 6 stations):
  • 9-inch finger bowls with distilled water
  • 600 ml beakers containing distilled water and dialysis tubing
  • 400 ml beakers (1 per group)
  • microscope slides and cover slips
Solutions (setup at each of 6 stations):
  • 1.0 liter stock bottle of distilled water for each of 6 groups
  • 250 ml stock bottle of 15% sucrose
  • 250 ml stock bottle of 30% sucrose
  • 30 ml Wheaton dropper bottle of distilled water
  • 30 ml Wheaton dropper bottle of spring water
  • 30 ml Wheaton dropper bottle of concentrated salt solution (20% NaCl)
  • 30 ml Wheaton dropper bottle of concentrated sugar solution (15% glucose)
Organisms (two supply beakers per table):
  • Elodea or Spirogyra in spring water
Other supplies:
  • dialysis tubing (1 inch flat) cut into 15 cm (approx. 7 in) pieces, soaking in distilled water in 600 ml beakers at each station
  • lens tissue
  • graph paper, 24 sheets per lab

Themes

  • All cells live in a aqueous environment.
  • Semipermeable membranes in organisms are chiefly phospholipid bilayers whose behavior is modeled by dialysis tubing.
  • The interplay of concentrations across membranes creates problems that living cells and organisms must solve.

Web Resources

  • Osmosis, Department of Physiology, University of Vermont
  • Osmosis, Cell and Molecular Biology, Colorado State University

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Last updated 12 June 2006 (JHW)