Experimenting with Light
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Introduction

Plants have the fantastic ability to create their own food. The process is called photosynthesis and uses energy from sunlight in combination with carbon dioxide and water to produce sugar and oxygen. Photosynthesis is the first step in the food chain which connects all living things.

In this experiment kids will manipulate the amount of light plants receive and collect data on the plants' varying growth rates. By making observations and measurements, the students will then analyze their data to draw conclusions about the relationship between plants and light.

This experiment is similar to the "Experiment with Water", except we're now studying the effects of light.

Materials Needed for Each Group of 3-4 Students:

• 2 identical plants. Consider using kitchen herbs-parsley, oregano, mint-to make the connection between plants and the food we eat.

• Labels for the sides of each pot.
• A sunny spot (indoors or out) for growing the plants.
• A dark place-cupboard, closet shelf.

Procedure

1. Divide class into groups of 3-4 students and provide each group with two plants similar in height and number of leaves.
2. Label one plant with the group name and the word "LIGHT." Label the other plant with the group name and the words "NO LIGHT."
3. Have groups record baseline measurements of each plant's height, the number of leaves and the color of the leaves.
4. Have students write a hypothesis for the experiment.
5. Place the plants marked "LIGHT" in a sunny spot, and those marked "NO LIGHT" in the dark location.
6. Regularly water both sets of plants. Check them every day and water them when the soil dries out. When watering potted plants, add water until it begins to drain from the bottom of the pot.
7. Take measurements of the plant height, leaf length, count the number of leaves, and note leaf color at least once a week. Notice how new leaves are affected by the experiment.
8. At the end of one month, have students analyze their data and draw a graph that contrasts growth rates. Students can write a conclusion and share their findings.

If you don't want to kill the plants, you can let the experiment last until they're showing enough signs of stress that the students understand the concept. You can attempt to revive your plant by putting it into the light. Water it lightly for the first week or so. Plants that haven't been actively photosynthesizing can't absorb a lot of water.

Discussion Questions

• What happened to the plants that received light during this experiment?
• What happened to the plants that did not receive light?
• Do plants need light to survive?

Experiment procedures courtesy of The Huntington Library.

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