When the blood glucose concentration decreases below the set point, a hormone is released from the pancreas.
Describe how the release of this hormone leads to the blood glucose concentration returning to the set point.
Outline why insulin can be described as an example of a cell-signalling molecule of the endocrine system.
With reference to Fig. 7.1, explain how negative feedback operates to control mean blood glucose concentration in the volunteers who ate meal A.
Suggest explanations for the changes in mean blood glucose concentration of the volunteers who ate meal B.
Suggest other environmental factors, apart from the time of day, that can contribute to stomatal closure.
Table 6.1 shows some of the events occurring during the closure of a stoma.
The events are not listed in the correct order.
Table 6.1
| event | description of event |
|---|---|
| A | water leaves the guard cells by osmosis |
| B | active transport of hydrogen ions out of the guard cells stops |
| C | stoma closes |
| D | plant is subjected to a change in environmental conditions |
| E | plant releases abscisic acid |
| F | calcium ions move into the cytoplasm of the guard cells |
| G | abscisic acid binds to receptors on the cell surface membrane of guard cells |
| H | guard cells become flaccid |
| I | water potential of the guard cells increases |
| J | potassium ions leave the guard cells |
Complete Table 6.2 to show the correct order of the events shown in Table 6.1.
Three of the events have been completed for you.
Table 6.2
| correct order | letter of event |
|---|---|
| 1 | D |
| 2 | |
| 3 | |
| 4 | |
| 5 | F |
| 6 | |
| 7 | |
| 8 | |
| 9 | |
| 10 | C |
Glomerular filtrate is formed by the process of ultrafiltration.
Describe the process of ultrafiltration.
Different mammals have different thicknesses of medulla relative to the size of the kidney.
Fig. 6.1 shows the relationship between the mean thickness of the medulla in kidneys of different mammals and concentration of urine produced by the kidneys.
Suggest an explanation for the relationship shown in Fig. 6.1.
Describe how a decrease in the water potential of the blood leads to an increase in the concentration of antidiuretic hormone (ADH) in the blood.
Binding of ADH to the ADH receptor triggers reactions within the cell. One of the first reactions is the production of cyclic AMP (cAMP).
State the term used to describe molecules such as cAMP in cell signalling.
On Fig. 1.1, draw arrows to show the direction of movement of water molecules after the cells of the collecting duct have responded to ADH.
Some people have a rare kidney disorder in which ADH is not able to bind to ADH receptors.
Suggest the effects of this disorder on osmoregulation.
Fig. 9.1 shows a longitudinal section of a human kidney.
Fig. 9.1
Name the regions of the kidney labelled X and Y in Fig. 9.1.
X ______
Y ______
A biosensor can be used to measure the concentration of glucose in urine.
Outline how a biosensor measures the concentration of glucose in urine.
Phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB) are enzymes involved in the regulation of blood glucose concentration.
Fig. 6.1 shows a cell-signalling pathway involving insulin, PI3K and PKB in a muscle cell.
Type 2 diabetes mellitus is a common disease. Some people with type 2 diabetes have a low concentration of PI3K in their muscle cells and cannot maintain their blood glucose concentration within normal limits.
With reference to Fig. 6.1, suggest why a low concentration of PI3K can lead to type 2 diabetes.
Fig. 9.1 shows a longitudinal section of a human kidney.
Fig. 9.1
Name the regions of the kidney labelled X and Y in Fig. 9.1.
X ______
Y ______
A biosensor can be used to measure the concentration of glucose in urine.
Outline how a biosensor measures the concentration of glucose in urine.
Calculate the percentage increase in blood glucose concentration, between 0 and 60 minutes, for the person with type 2 diabetes.
answer ______
Suggest ways in which people with type 2 diabetes can help to control their condition.
Glucagon has a role in the control of blood glucose concentration.
Describe the cell signalling pathway involving glucagon, and describe how this pathway leads to a change in the blood glucose concentration.
When the water supply to a plant is reduced, the concentration of abscisic acid (ABA) in the leaves increases.
ABA binds to receptors in the cell surface membranes of guard cells. This triggers a series of events in the cells, which results in stomatal closure.
Fig. 8.1 is a diagram of part of a guard cell showing some of the events that occur when ABA binds to its receptor.
Fig. 8.1 shows that calcium ions are involved in the events within a guard cell that result in stomatal closure.
Outline the role of calcium ions in the response of the guard cell to a reduced water supply and explain how this response results in stomatal closure.
Identify X in your answer.
Explain, using examples, why the homeostatic control involving the opening and closing of stomata is important for the efficient functioning of plants.