hard · Enhanced ACT Science
Scientist 1: Migratory birds sense Earth's magnetic field through a light-driven chemical reaction in the eye. Blue light striking a protein called cryptochrome creates a pair of radicals whose chemistry depends on the field's direction. Because this compass needs light, birds should lose their magnetic orientation in complete darkness but keep it under dim blue light.
Scientist 2: Birds detect the field with tiny magnetite crystals in the beak, wired to nerves. These iron-rich particles physically twist to align with the field, mechanically stimulating the nerve regardless of light. On this model, orientation should persist in complete darkness, but severing the beak nerve, or a brief strong magnetic pulse that reorders the crystals, should disrupt it.
Tested in complete darkness, the birds still orient correctly, but a brief strong magnetic pulse to the beak leaves them disoriented for days. Together these results support which position?
- Scientist 1, because a light-driven eye compass can still work in complete darkness.
- Scientist 2, because orientation held without light and a beak pulse then disrupted it.
- Scientist 1, because the strong magnetic pulse must have activated the cryptochrome.
- Both scientists, because light and magnetite each played a measurable part here.
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