A medicine temporarily reduces the secretion of thyroxine by a person's thyroid gland. The medicine does not damage any endocrine gland.
The table shows measurements made after the person stops taking the medicine. Each measurement is given as a percentage of the person's normal value.
| Time after stopping the medicine in days | Thyroxine concentration in % | TSH concentration in % | Metabolic rate in % |
|---|---|---|---|
| 0 | 60 | 180 | 80 |
| 4 | 85 | 140 | 90 |
| 8 | 100 | 100 | 100 |
A student makes two claims.
Claim 1: thyroxine controls metabolic rate.
Claim 2: negative feedback reduces TSH secretion as the thyroxine concentration returns to normal.
Explain how the results support both claims. Use data from the table in your answer.
89 exam-style questions on Edexcel GCSE Biology 7.1 Hormones and coordination, covering 7.1.1 Endocrine glands and hormone transport, 7.1.2 Adrenalin and fight or flight, and 7.1.3 Thyroxine and negative feedback. Each one has a worked solution and a mark scheme showing where the marks go.