The pituitary gland releases a hormone called TSH. TSH stimulates the thyroid gland to release thyroxine. Thyroxine increases the metabolic rate. The thyroid gland needs iodine from the diet to make thyroxine.
The Table shows the concentrations of TSH and thyroxine in the blood of three people.
Table
| Person | Concentration of TSH in arbitrary units | Concentration of thyroxine in arbitrary units |
|---|---|---|
| A (normal) | 2 | 15 |
| B | 25 | 4 |
| C | 0.1 | 40 |
Person B has very little iodine in their diet.
Use the idea of negative feedback to explain the results for person B.
Person C has a tumour in the thyroid gland. The tumour releases thyroxine all the time.
Explain why person C has a very low concentration of TSH.
Suggest one symptom that person C may have.
84 exam-style questions on OCR GCSE Biology 3.2 Coordination and control – the endocrine system, covering 3.2.1 Principles of hormonal coordination and control, 3.2.2 Roles of thyroxine and adrenaline, 3.2.3 Hormones in human reproduction, 3.2.4 Interactions of reproductive hormones, 3.2.5 Hormones in contraception, 3.2.6 Hormones in reproductive technologies, 3.2.7 Plant hormones in growth and coordination, 3.2.8 Effects of plant hormones, and 3.2.9 Uses of plant hormones. Each one has a worked solution and a mark scheme showing where the marks go.