Module C. Aging

(Level of difficulty **)

Question: Why do plants (or plant organs) get old and die?

Materials you will need:
•2 empty rinsed plastic yogurt containers or single-use cups (any size)
•Small scissors
•An outside tree with green leaves
•A ripe banana
•2 large zip-lock bags to fit the cups

•Locate a tree outside with green leaves (maple, oak, elm, tulip and many other broad-leaved trees would work)
•Collect 4-6 identical leaves by cutting the stalk of the leaf (called petiole) with scissors
•Fill two cups with water
•Place 2-3 leaves in one cup and the remaining 2-3 leaves in another cup
•Put each cup with leaves into a plastic bag, being careful not to spill the water
•Into one of the two bags, add a ripe unpeeled banana
•Seal both zip–lock bags tightly
•Observe what happens to the leaves over time in the bags with and without the banana

Helpful hints and suggestions:
•You may want to label the cups (for example, “banana” and “no banana”), so that after your experiment is done you will not get confused which cup is which.
•You do not need to submerge the leaves in the water: as long as the stalks of the leaves (called petioles) are touching the water, the leaves should be fine
•For this experiment instead of a tree you can use a houseplant such as violet, philodendron or another broad-leaved plant, but make sure you ask an adult for permission first!

Expected results:
•Leaves that were placed in a cup of water next to a banana should age faster (they will turn yellow).  Ripe banana produces a gas called ethylene that is trapped by the plastic bag.  Ethylene then promotes leaf aging.

Follow-up questions:

•Did you know that ethylene is a stress hormone in plants and can induce not only aging but also fruit ripening?
•Do you think the results of this experiment would be different if you were to use another fruit or vegetable in a bag instead of a banana?
•Do you know the type of tree (the species) you did your experiment on?
•Would the outcome of the experiment be different if you used leaves of another variety of trees?
•Why do you think a plant would want to make ethylene to promote its own aging?  In other words, why is it beneficial (good) for the plant to kill off its own parts (Hint: think of damaged or infected leaves or ripe fruits)?