Elodea (pondweed) cells

Materials

• Glass microscope slides
• Plastic cover slips
• Paper towels or tissues
• Salt solution (6 g salt dissolved in 100 ml of water or approx. 2 teaspoons salt in a cup of water)
• Elodea
• Water

See information on suppliers here.

Methods

1. Pick off an entire healthy looking Elodea leaf, with fingers or small scissors and place it on the microscope slide.
2. Add a drop of water (hypotonic solution) and a coverslip and observe the chloroplasts (green structures) and the cell walls.
3. Add a drop of salt solution (hypertonic solution) to the side of the coverslip and observe the cell shrinking (optional).

When the salt solution is added, the salt ions outside the cell membrane cause the water molecules to leave the cell through the cell membrane causing it to shrink into a blob in the centre of the cell wall. The movement of water molecules is called osmosis.

Elodea is a genus of submerged aquatic plants used in aquariums. You should be able to buy this from pet shops. If not, you can purchase it from a school supplier. Elodea canadensis is a species that works well for this activity, because it has thin, straight leaves. However, most other species are satisfactory.