Teacher sheet · Ages 15–16 · about 45–50 minutes
Metamorphosis, hormones and survival
Lesson page: echoesof.science/school/animal-life-cycles/ages-15-16/ · Pupil worksheet: echoesof.science/school/animal-life-cycles/ages-15-16/print/
Learning aims
- Explain the hormonal control of metamorphosis in insects (ecdysone, juvenile hormone) and amphibians (thyroxine).
- Describe what happens inside a pupa and during tadpole metamorphosis.
- Use the chick embryo timeline in calculations with units.
- Model survival with probability; compare expected and observed values and discuss sample size.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: a caterpillar and a butterfly share the same DNA. So why do they look so different? |
| 10 min | Read the text; compare insect and amphibian hormone pathways. |
| 20 min | Survival model with dice; pool class data. |
| 5 min | Calculations: chick timeline and caterpillar growth. |
| 5 min | Quiz, or the Insect or amphibian? game as homework. |
Materials for the experiment
- 100 counters, beans or paper squares per group
- A dice per group (or a random-number generator)
- Record table and graph paper or a spreadsheet
Safety: No live animals are used. Keep counters away from very young children (choking hazard) if the room is shared.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Metamorphosis is controlled by the animal 'deciding' to change. | It is controlled by hormones: ecdysone and juvenile hormone in insects, thyroxine in amphibians. |
| The tadpole's tail falls off. | The tail is broken down and absorbed: its cells are destroyed and eaten by phagocytic cells. |
| If 3 out of 100 survive in one sample, exactly 3% always survive. | Survival is random; small samples vary, and pooling many samples gives a better estimate. |
Worksheet answers
- Insects: brain hormone → prothoracic gland → ecdysone (moulting); juvenile hormone keeps the larval form, its fall allows pupa and adult. Amphibians: pituitary thyrotropic hormone → thyroid → thyroxine, which drives loss of gills and tail.
- 500 × 1/2 × 1/3 × 1/6 ≈ 13.9, so about 14 adults; random variation means a group's count can be higher or lower.
- 10 ÷ 21 × 100 ≈ 48%.
- Even if most eggs and tadpoles die from frost or predators, laying very many increases the chance that some survive to adulthood and breed.
Quiz answers
- Which hormone causes an insect to moult? Ecdysone. Ecdysone, from the prothoracic gland, is the moulting hormone.[5]
- What does juvenile hormone do? It keeps the larval form while it circulates. When juvenile hormone falls, the larva becomes a pupa and then an adult.[5]
- Which gland makes thyroxine to drive amphibian metamorphosis? The thyroid. The pituitary stimulates the thyroid to make thyroxine.[5]
- What grows into adult wings and legs inside the pupa? Imaginal discs. Imaginal discs are cell clusters set aside in the embryo.[4]
- A chick's heart starts beating at about 44 hours. What fraction of the 21-day incubation is that? About 9%. 44 h ÷ (21 × 24 h) = 44 ÷ 504 ≈ 0.087, about 9%.[6]
- A caterpillar hatches at 1 mg and grows to about 1,000 times its birth weight. What is its final mass? About 1 g. 1 mg × 1,000 = 1,000 mg = 1 g.[1]
Going further
Research a hemimetabolous insect such as a dragonfly and compare its life cycle with a butterfly's. Discuss why larvae and adults may live in very different places, and check claims against museum or university sources.
Sources used in this lesson
- [1] The Butterfly Life Cycle Explained (American Museum of Natural History): reliability High
- [2] Frogspawn, tadpoles and froglets (Natural History Museum, London): reliability High
- [4] Insect Metamorphosis: The Key to a Fresh New Start (Carnegie Museum of Natural History): reliability High
- [5] Animal development: Metamorphosis (Encyclopaedia Britannica): reliability High
- [6] Stages of Chick Embryo Development (Mississippi State University Extension): reliability High
- [7] Mammals (Australian Museum): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/animal-life-cycles/sources/
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