A healthy adult is given a small injection of TRH into the blood. The table shows hormone concentrations before and after the injection.
| Time after injection / hours | TRH concentration / pg cm⁻³ | TSH concentration / mIU dm⁻³ | Thyroxine concentration / nmol dm⁻³ |
|---|---|---|---|
| 0 (before injection) | 5.0 | 2.0 | 100 |
| 1 | 30.0 | 8.0 | 102 |
| 8 | 5.0 | 5.0 | 125 |
| 24 | 2.0 | 1.0 | 118 |
| 72 | 5.0 | 2.0 | 100 |
Explain the sequence of changes in hormone concentrations after the injection. Include in your answer how the person's metabolic rate at 8 hours would compare with their metabolic rate before the injection.
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.