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Life Science: Brassica & Butterfly System

Brassica & Butterfly Life Cycles

What happens during a typical plant life cycle? What about the life cycle of a familiar insect, like a butterfly? This activity explores the life cycles of Fast Plants, or Brassica rapa, and Pieris rapae, the cabbage white butterfly.

Materials Needed


To prepare

  • Order your Fast Plants seeds and butterfly eggs, and buy seeds for the Brassica Nursery from a local garden shop (radish, turnip, and/or mustard seeds). NOTE: You’ll need to plant the seeds about five days before the butterfly eggs arrive, so time their arrival accordingly.
  • Before the Fast Plant seeds arrive, build the Bottle Growing System, Light House, Brassica Nursery, and Brassica Barn.
  • When they arrive, plant the Fast Plant seeds in the Bottle Growing System and place it in the Light House.
  • On the same day or a few days earlier, plant the seed mix in the Brassica Nursery and place it in the Light House.

When the butterfly eggs arrive

During the study period

Both life cycles will take about 30–40 days to complete. During this time, make observations every 2–3 days. Use your Brassica & Butterfly Data Sheets (PDF) to record what you observe and answer questions.

Visit www.fastplants.org for in-depth information on the Brassica and the butterfly.

Activity Questions

Brassica questions

  • How does a seed germinate?
  • What environmental conditions do seeds need for germination?
  • Where do new plant parts (roots, stems, leaves, flowers, and pods) develop?
  • How do plants get the carbohydrates (sugar) they need for energy to grow?
  • What is the purpose of each structure (roots, stems, leaves, flowers, and pods)?
  • Why are insects attracted to the flowers?
  • Do all seeds on a plant have the same mother? The same father? Explain.
  • Are the seeds alive? Justify your answer.

Butterfly questions

  • How do the larvae hatch from the eggs?
  • What clues indicate that larvae are present, even if you can’t locate them?
  • What do the larvae eat?
  • Where would you expect to find larvae?
  • What do the larvae expel?
  • Each larva has an exoskeleton. What is the function of the exoskeleton?
  • How do the larvae grow larger? What happens to the exoskeleton?
  • How do the larvae become butterflies?
  • What indicates that a larva is ready to form a chrysalis?
  • What indicates that a butterfly is ready to emerge from a chrysalis?
  • Where do female butterflies tend to lay their eggs? Why?
  • What is the difference between the food for the larvae and the butterflies?
  • What food needs to be present for another generation of butterflies to survive?

Brassica & Butterfly questions

  • How does the Brassica depend on the butterfly?
  • How does the butterfly depend on the Brassica?

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