A research team briefly exposes insect eggs to radiation from a sealed gamma source. The source is then returned to its shielded store. The source remains sealed throughout.
The team examines 200 cells from the eggs at two different times.
| Time | Number of cells with altered DNA |
|---|---|
| Before exposure | 1 |
| 12 hours after the source is removed | 32 |
Explain why the eggs stop being irradiated when the source is removed, and explain how the results in the table show that an effect of the exposure remains 12 hours later.