From Seed to Seed:
Plant Science for K-8 Educators

Activity 26: Plant-in-a-Bag

Grades: K-8

Associated Lesson Topics:

• Transpiration

National Standards:

• SCIENCE: Standard A, Standard C

Planting the Seed...

Ask students to remove a leaf from the top of a plant. Have them break the leaf open and observe its contents. What do you notice? Where do you think the moisture comes from? How might it find its way to the leaf?

Teacher Information:

We can't usually see the water that exits a plant during transpiration. This is because the water is in the form of a gas known as water vapor. When you place a bag over the plant, the bag traps the water vapor and converts it back into water. The water, therefore, appears as condensation on the inside of the bag.

You can use paper towels and water to teach your students about the cohesion-tension theory. If you place the corner of a paper towel in water, the water will be drawn up over the paper towel. The water that is left behind is attracted to the water that has been absorbed and is pulled along with it. This is, essentially, what is happening in the plant. Chain reactions cause the water to be pulled up and out of the plant.

Necessary Materials:

• A garden or potted plant.
• Large plastic bag.
• String.

Procedure:

• Water the plant or plants.
• Place a clear plastic bag over all of the leaves.
• Tie the bag loosely with string around the stem.
• Leave in the sun for a day. If you are conducting this experiment inside with a potted plant, place it on a windowsill.
• Have students record their observations in their journal.
  

Harvesting the Crop...

While you are waiting to see what happens, encourage the students to make predictions about what is going to take place. What do you expect to happen? After observing the water on the inside of the bag, ask, Where do you think the water came from? How do you think a plant's ability to move water might help it survive? How often do you think the plant does this?

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