(a(i))[1]
Name the membrane component type that acts as a receptor in the cell surface membrane.
(a(ii))[1]
State how GLP-1 reaches the pancreas.
(b)[2]
GLP-1 reduces the secretion of glucagon by $\alpha$ cells in the pancreas. Describe two liver processes that are promoted by glucagon.
(c)[1]
Suggest one reason why GLP-1 lowers appetite.
(d)[3]
GLP-1 slows down the emptying of the stomach. This is an example of negative feedback. Explain what is meant by negative feedback.
(e)[3]
A transcription factor is involved in the production of GLP-1. An insertion mutation in the gene that codes for the transcription factor can affect the production of GLP-1. Outline the effect of an insertion mutation on the production of GLP-1.