A research team studies the control of thyroxine, TRH and TSH in healthy adults. Each adult is given a small dose of thyroxine. Several hours later, the concentration of TSH in the blood has decreased.
The researchers conclude that the complete negative feedback response has occurred.
Why is this conclusion not supported by the evidence?
The study does not show that reduced thyroid secretion returns thyroxine towards its normal concentration.
The study does not show that the thyroid releases TRH when the TSH concentration decreases.
The study does not show that a lower TSH concentration makes the thyroid secrete more thyroxine.
The study does not show that TSH directly lowers the metabolic rate of body cells.
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.