Scientists connected samples of functioning human hypothalamus, pituitary gland and thyroid gland tissue with a circulating culture fluid. A pump was then switched on to add thyroxine and maintain its concentration in the fluid.
The table shows each hormone concentration as a percentage of its concentration before the pump was switched on.
| Time | Thyroxine concentration (%) | TRH concentration (%) | TSH concentration (%) |
|---|---|---|---|
| Before the pump was switched on | 100 | 100 | 100 |
| 60 minutes after the pump was switched on | 160 | 42 | 35 |
Explain the changes in TRH and TSH concentrations after the pump was switched on. Predict the effect, compared with before the pump was switched on, on the amount of thyroxine secreted by the thyroid tissue and on the metabolic rate of the tissues.
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.