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

Activity 18: Luminous Lessons

Grades: K-8

Associated Lesson Topics:

• Plant requirements (light)
• Adaptations

National Standards:

• SCIENCE: Standard A, Standard C (K-4)
• MATH: Data Analysis and Probability Standard

Planting the Seed...

What words would you use to describe a healthy plant? What image does the phrase "healthy plant" conjure up in your mind? Is it tall? A certain shade of green? Does it have many leaves or just a few? What does an unhealthy plant look like? Compile a list of students' ideas about the characteristics of healthy and unhealthy plants. Keep in mind that this list is subjective-your students should create their own definition of "healthy" and use it to assess the health of their plants at the end of this investigation.

Teacher Information:

In this activity students will grow the same species of plant in different light conditions to determine which support optimumal plant growth. To obtain an accurate assessment of the effects of light on growth, they must keep all other conditions identical for each plant (e.g., soil composition, pot size, potting medium, water, fertilizer). This same type of experiment can also be conducted for other environmental factors (e.g., moisture, nutrients).

Many teachers are confused when the plant that students kept in the dark or shade becomes taller than the one grown in the light. In low light levels, gibberellin-a plant growth regulator-increases internode length, allowing the plant to stretch as though reaching for light. At the extreme, the stem grows so tall that it becomes too weak to support the plant, a condition called etiolation. This phenomenon is familiar to seed starters-especially those who forget to turn on the lights once their seeds have sprouted!

Because the plant is taller, it is not necessarily healthier. Encourage your students to look at the overall health of the plant. Being tall isn't the only measure of plant health-and in this case isn't even a good one!

For K-4 students, this activity can involve partial inquiry. Provide the students with the experimental design (below) and ask them to hypothesize about which plant they think will be healthiest. On the other hand, students in grades 5-8 can participate in the full inquiry process. Students should be encouraged to design the entire experiment, from the initial question through the analysis.

Necessary Materials:

• Classroom: Two plants of the same species.
• Garden: Seeds of the same species.
• Planting materials.

Procedure:

• If you are conducting this experiment in the classroom, use young plants that are already established in pots. If you are conducting this experiment in the garden, you can begin with seeds or plants.
• In the classroom, place one plant in a dark closet and the other on the windowsill or under fluorescent lights. Keep plants in their respective spots for several weeks, watering them equally, and having students make routine observations along the way.
• In the garden, plant seeds in locations ranging from full sunlight to shade. Have students make routine observations on these plants. Which seeds took longer to germinate? Which plants grew the fastest?

Harvesting the Crop...

Based on the list of healthy/unhealthy plant characteristics that you compiled earlier, which plant(s) is healthier? How sturdy is the stem of the plant grown in the dark or shade compared to the plant grown in the light? Which one could handle a strong wind or rain storm more successfully? Is there a difference in the color of the plants? What can you infer about the ideal light condition for these plants? Can you think of any ways that those plants grown in the dark might adjust to access more light? Here you can begin or continue a discussion on adaptations.

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