Experiment: Access to Light

Materials    

1. Two identical potted plants that typically grow in full sunlight. Good plants for this include pansy and petunia
2. Sunny outdoor area or a sunny windowsill
3. Dark place in which plants can be placed, such as a cupboard
4. Experiment Log (provided)
5. Ruler
6. Water
7. Writing utensil

Steps

Note: See section “Expanding the Activity” for additional elements you may choose to include.

1. Use the Experiment Log to write a hypothesis for the experiment and to make initial (baseline) measurements of each plant’s height, number of leaves and flowers, and their respective color.  These may change during the experiment, so it is important to record these measurements accurately at this time. 
2. Label one plant “light” and one plant “no light.”
3. Place the plant labeled “light” in one area in a sunny location outside or on a sunny windowsill. 
4. Place the plant labeled “no light” in a place that is completely dark. If possible, choose a cupboard that will not be opened for other reasons during the experiment.
5. Check both plants every day, and water them when the soil begins to dry out.  In this experiment, the amount of light is the only independent variable, so it is important to keep plants in both locations evenly moist.
6. Repeat measurements of both plants once a week.  Record results on the Experiment Log.
7. Carry out the experiment for 4-5 weeks and then discuss the results.

Discussion Questions

1. What happened to the plants that received enough light during this experiment?
2. What happened to the plants that did not receive any light?
3. Do you think plants need light to grow?  Why or why not?
4. How long did it take for the plants that did not receive any light to show signs of stress?  What signs of stress did you notice?