The release of thyroxine is controlled by negative feedback. The pituitary gland releases TSH, which stimulates the thyroid gland to release thyroxine. The concentration of thyroxine in a person's blood rises above the normal level. Which statement describes what happens next?
The pituitary releases more TSH, so the thyroxine level keeps rising.
The pituitary releases less TSH, so the thyroxine level falls to normal.
The thyroid releases more TSH, so the thyroxine level falls to normal.
The thyroid stops responding to TSH, so the thyroxine level stays high.
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.