Researchers took blood samples from vessels entering and leaving an active thyroid gland. The thyroxine concentration was higher in the blood leaving the gland.
They added equal volumes of plasma from each sample to separate groups of the same type of cultured body cells. The rate of chemical reactions in the cells increased with plasma from the blood leaving the gland, but did not increase with plasma from the blood entering it.
Explain what the two observations show about the thyroid gland and the route by which its effect reaches the 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.