A gland in a small mammal releases chemical Q into the blood. Scientists investigated the effects of Q on organs R and S.
Organs R and S were maintained in an apparatus with a blood supply but no connection to any nerves. The scientists collected blood before and after stimulating the gland. They separated the blood into plasma and red blood cells and supplied equal volumes of each preparation to the organs.
For one treatment, they removed most of Q from the plasma without changing the concentrations of the other substances in the plasma.
| preparation supplied to the organs | concentration of Q (ng per cm³) | mean change in activity of organ R (%) | mean change in activity of organ S (%) |
|---|---|---|---|
| plasma collected before stimulation | 0.2 | 1 | 0 |
| plasma collected after stimulation | 8.4 | 36 | 2 |
| plasma collected after stimulation, with most Q removed | 0.1 | 2 | 1 |
| red blood cells collected after stimulation | 0.1 | 1 | 1 |
Explain how the results support the conclusions that Q acts as a hormone and that R is a target organ for Q.
Explain why a response caused by Q may continue after the gland is no longer stimulated, whereas a response caused by nervous control usually stops sooner.
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.