BACKGROUND:

Elodea plants are found in fresh water, and are common fish tank plants. Students will observe many chloroplasts throughout the cells. Photosynthesis is occurring in each cell in the plant. The Elodea plant is much simpler (less complex structurally) than the onion or cork. An onion bulb is the root of the onion plant.

Cork is found as the outer layers of stems and roots of woody plants and also as the protective layer that forms when a plant is damaged. Water conservation and protection are the functions of cork. In the case of the oak cork such a profuse formation of cork occurs that this tissue is removed and used commercially (ie. cork stoppers, life preservers). Removing of the cork does not harm the tree as long as it has time to regrow another thick layer every 3 to 4 years.

PROCEDURE:

1. Place a small, thin piece of the elodea, onion and cork on one slide. Put a little iodine on each (less than a drop). If you are using the Swift-GH you do not need the cover slips. If you are using a transmitting light microscope, make sure the pieces of elodea, onion, and cork are very thin. You may need to place a drop of water and use a cover slip on top of the specimens.
       
2. Emphasize with students that they have looked at 3 types of plants and these do not look like the ideal pictures of the pre-lab worksheet. The common structure that can be seen in all 3 specimens is the cell wall. The pictures below should help you illustrate the differences with your students. Plants are more complex than most books present. Students should be aware of this. Looking at cork tissue under the microscope, students should see empty cells. There are no chloroplasts, but very thick cell walls. Cork does not undergo photosynthesis, so students should not see chloroplasts.