Fig. 10.1 shows how blood glucose concentration and blood glucagon concentration are related, as measured over $90$ minutes in a healthy person. The person had eaten nothing during the three hours before the readings were taken. Explain the relationship shown in Fig. 10.1. Blood glucose concentration is measured in $\text{mmol dm}^{-3}$ and blood glucagon concentration is measured in $\text{pmol dm}^{-3}$.
The passage below describes cell signalling. Fill in the gaps using the most suitable scientific terms. Cells need to communicate with their surroundings and with other cells nearby. This is called cell signalling. Cells in mammals take part in a complex communication network with one another. For example, liver cells detect signals using receptors in their cell surface membranes. Glucagon binds to the receptors because its shape is ................................ . This binding activates a ................................ , leading to stimulation of the enzyme ................................ .