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

Activity 19: Twists and Turns

Grades: K-4

Associated Lesson Topics:

• Light requirements
• Photosynthesis
• Phototropism

National Standards:

• SCIENCE: Standard A, Standard C

Planting the Seed...

What do plants need in order to grow? Can you infer how plants use light? If plants are not getting the light they need, do you think there is anything that they can do to get more?

Teacher Information:

Plants need light in order to photosynthesize. They need to photosynthesize in order to produce the food they need to survive. It is safe to say, then, that light is a very important resource to plants. Witnessing a plant as it bends toward the light is evidence of this. This bending-called phototropism-results from the movement of auxin, a chemical that regulates plant growth. Auxin accumulates on the dark side of the stem and promotes elongation of those cells, enabling the stem to bend toward the light. Phototropism enables otherwise immobile plants to move and capture more light. In this activity, students will learn that plants need light so much that they will do just about anything to get it!

Necessary Materials:

• Cardboard box with dividers and a top-the box that wine is shipped in is perfect.
• Exacto knife.
• Bean seeds.
• Clear plastic wrap.
• Pots small enough to fit in one of the divided sections of the wine box.
• Potting soil.
• Duct tape.

Procedure:

• Cut holes in the dividers to make a maze. The maze should end with a hole in the top of the box. Make the holes large enough to allow a seedling stem and leaves to pass through.
• Plant two bean seeds in a pot, water them and cover the pot with clear plastic wrap. Place in sunlight and allow the seeds to germinate.
• Once the seeds have germinated, place the pot in a corner section in the box.
• Close and seal the box with tape. It is important that the only light to reach the plant comes from the hole in the top of the box.
• Keep the box closed for two to three weeks, opening it only to water the beans every two or three days.

Harvesting the Crop:

What has happened to the plant? Why do you think this has happened? How do you think the plant is able to find the light? Can you infer how it makes the stem bend in order to get there? With older kids, you can begin to talk about the role of plant growth regulators in this process.

To make this activity more complex, have students plant two bean seeds in the same size pot and place it in a location where it receives plenty of sunlight at the same time as they are conducting the maze experiment. Water this pot at the same time and with the same amount of water as the pot in the box. At the end of the experiment, compare the two sets of plants. How do these two plants compare? Is the curviness in the stem of the boxed plant the only difference? Which one looks healthier? Which one is more green? Which one is taller? Which one has a greater distance between nodes?

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