The hormone glucagon is an example of a cell signalling molecule. Table 2.1 lists the main events that occur when the blood glucose concentration decreases below the set point. The events are not listed in the correct order. [Table 2.1]

1. (a)Complete Table 2.2 to show the correct order in which these events occur. Three of the events have already been placed in their correct order. [Table 2.2][4]
2. (b)(i)An investigation was carried out to measure the rate at which glucose is provided for respiration from three different sources of glucose: • a meal • glycogenolysis – the breakdown of glycogen • gluconeogenesis – production of glucose from non-carbohydrate molecules. After a person ate a meal, the rates at which glucose was provided for respiration from the three different sources were measured at regular intervals over a 24-hour period. During this period, no food was eaten. [Figure 2.1] shows the results of this investigation. State the time after the meal when the rate at which glucose was provided from the meal for respiration was the same as the rate at which glucose was provided from glycogenolysis for respiration.[1]
3. (b)(ii)State the first time after the meal when all of the glucose for respiration was provided by gluconeogenesis.[1]
4. (b)(iii)Name the homeostatic mechanism by which blood glucose concentration is maintained at a set point.[1]
5. (b)(iv)In humans, carbohydrates such as glucose are not the only respiratory substrates. Name two non-carbohydrate respiratory substrates in humans.[2]

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