Water Retention of a Cactus Leaf- Free Lesson

Plants need Water and Sunlight to Survive, but what about plants that live in the desert where there is very little to no rain?

The students will:

1) Measure the water capacity of a cactus leaf by comparing the measurement of the cactus before and after drying the leaf.
2) Identify the characteristic of the leaf that allows the cactus to retain water.

1) Cactus Leaf (Can be purchased from some grocery stores in the produce aisle.)

2) Scale

3) Sunny Spot near a window

4) Paper towel

5) Gardening Gloves

6) Wax Paper

7) Cookie Sheet

Activity 1:
1) Examine the texture of the cactus leaf; cacti often have a waxy coating on their stems to prevent water loss.

2) Wet three pieces of paper towel.

3) Lay one paper towel flat.

4) Roll the next piece of paper towel up and clip it with a paper clip so it stays rolled up.

5) Roll the third paper towel in a piece of wax paper and clip it with a paper clip as well.

6) Lay the 3 sheets of paper towel on the cookie sheet and let them lay out for 24 hours. The next day check your paper towels. The flat paper towel will be dry and the paper towel rolled up with be slightly damp. However the paper towel that was wrapped in the wax paper will still be wet! The wax paper is similar to the coating on a cactus leaf which prevents the loss of water allowing the cactus to survive in extremely dry and hot climates.

Activity2:
1) Wear gardening gloves when handling, the leaf is prickly.

2) Weigh the cactus leaf on the scale. Record the weight.

3) Lay the cactus leaf on newspaper or paper towel and place it on a window sill to dry out.

4) Each day, weigh the cactus leaf and record the weight. The leaf will become wilted once it has lost most of its water or the weight will not noticeably change.

5) Have students take the data and convert the weight of the cactus from grams to milligrams.

Talk about the cactus and the climate region cacti are found in. Discuss that the appearance of the cactus is due to its adaptations to live in dry climates to conserve water.

Discuss with students the results of their observations, how do the features of a cacti help the plant to survive dry and hot climates?

Cacti produce fruits such as dragon fruit or the prickly pear.  Cactus leaves are also edible as some are chopped up and added to salads and sometimes they are steamed like green beans.