A-Level · Biology · AQA · Mark scheme decoded
AQA A-Level Biology: Regulation of Blood Glucose Concentration — mark scheme explained
The short answer
Understanding how blood glucose concentration is regulated is crucial in A-Level Biology, as it involves multiple physiological processes and hormones that work together to maintain homeostasis. This section delves into the factors influencing blood glucose levels, the role of the liver, and the actions of insulin, glucagon, and adrenaline.
The question
Explain how insulin controls glucose uptake by muscle cells.
[Paraphrased for study — not reproduced from any exam paper.]
Mark scheme, decoded
How the examiner actually awards the marks on this topic.
Gradora's own decode of the marking approach — not the exam board's published mark scheme.
How marks are awarded
For descriptive questions, marks are typically awarded for clear and concise explanations that demonstrate a deep understanding of the topic. For comparative questions, marks are given for accurately identifying similarities and differences. For discussion questions, marks are allocated for considering multiple aspects and providing well-reasoned arguments.
What the command words demand
- Explain
- Provide a detailed description of the concept, including relevant principles and relationships.
- Describe
- Give a clear account of the process or mechanism without necessarily providing an explanation.
- Compare
- Highlight the similarities and differences between two or more concepts or processes.
- Discuss
- Consider multiple aspects of a topic, including causes, effects, and management strategies.
Model answer
A full-mark response to the question above, worked through step by step.
Timing: Allocate approximately 5-7 minutes per question to ensure you have enough time to carefully read the problem, provide a detailed response, and check your work.
- Insulin is produced by the beta cells of the pancreas and released into the bloodstream in response to high blood glucose levels.1 mark
- Insulin binds to receptors on the surfaces of target cells, such as muscle cells.1 mark
- Binding of insulin to its receptor triggers a signaling cascade within the cell.1 mark
- This signaling cascade promotes the insertion of glucose transporter proteins (GLUT4) into the cell membrane.1 mark
- The presence of GLUT4 in the cell membrane allows glucose to enter the muscle cells more efficiently, lowering blood glucose levels.1 mark
Final answer: Insulin binds to receptors on muscle cells, promoting the insertion of GLUT4 transporters into the cell membrane, allowing glucose to enter the cells and lower blood glucose levels.
Work through every step correctly and you earn all 5 marks.
Another worked example
Describe the role of glucagon in maintaining blood glucose levels during fasting.
- During fasting, blood glucose levels drop due to reduced dietary intake.0 marks
- The alpha cells of the pancreas detect this decrease and release glucagon into the bloodstream.1 mark
- Glucagon binds to receptors on liver cells, activating adenylate cyclase.1 mark
- Adenylate cyclase converts ATP into cyclic AMP (cAMP), which acts as a second messenger.1 mark
- cAMP activates protein kinase, which phosphorylates and activates enzymes involved in glycogenolysis and gluconeogenesis.1 mark
- Glycogenolysis breaks down stored glycogen into glucose, which is released into the bloodstream to raise blood glucose levels.1 mark
- Gluconeogenesis synthesizes new glucose from non-carbohydrate sources like glycerol and amino acids, further contributing to maintaining blood glucose levels.1 mark
Final answer: Glucagon activates enzymes for glycogenolysis and gluconeogenesis in the liver, breaking down stored glycogen into glucose and synthesizing new glucose from non-carbohydrate sources to maintain blood glucose levels during fasting.
Work through every step correctly and you earn all 6 marks.
Common mistakes
Confusing the actions of insulin and glucagon.
Why it happens: Students may mix up the roles of these hormones, leading to incorrect answers in questions about blood glucose regulation.
Fix: Remember that insulin lowers blood glucose by promoting glucose uptake and storage, while glucagon raises blood glucose by promoting glycogen breakdown and gluconeogenesis.
Failing to explain the role of the liver in glucose regulation.
Why it happens: Students may overlook the importance of the liver's functions in maintaining blood glucose levels.
Fix: Practice explaining how the liver performs glycogenesis, glycogenolysis, and gluconeogenesis to regulate blood glucose.
Misunderstanding the second messenger model.
Why it happens: The steps involved in the second messenger model can be complex, leading to confusion or incomplete explanations.
Fix: Break down the process into clear steps: hormone binding, adenylate cyclase activation, cAMP production, protein kinase activation, and enzyme phosphorylation.
Confusing type I and type II diabetes.
Why it happens: Students may mix up the causes and management strategies for these two types of diabetes.
Fix: Remember that type I diabetes is caused by autoimmune destruction of beta cells and requires insulin therapy, while type II diabetes involves insulin resistance and can be managed through lifestyle changes and medication.
Failing to explain the role of physical activity in blood glucose regulation.
Why it happens: Students may overlook the impact of exercise on blood glucose levels.
Fix: Practice explaining how physical activity increases glucose uptake by muscle cells, helping to lower blood glucose levels.
Not providing a clear explanation of gluconeogenesis.
Why it happens: Students may struggle to describe the process of synthesizing new glucose from non-carbohydrate sources.
Fix: Practice explaining how glycerol and amino acids are converted into glucose in the liver during fasting or prolonged exercise.
Where the marks go
The question types you’ll meet on this topic and the marks each one carries — so you know what to expect and where to focus.
| Question type | What you’re asked to do | Marks |
|---|---|---|
| Hormonal Control Mechanism | Describe how insulin triggers glucose uptake into muscle cells via receptor signalling and GLUT4. | 5 |
| Describe Hormonal Control | Describe how glucagon acts during fasting to raise and maintain blood glucose levels. | 6 |
| Explain Mechanism | Describe how adrenaline triggers a cascade via receptors, cyclic AMP, and enzyme activation in liver cells. | 5 |
| Compare Diabetes Types | Identify differences in causes and management between type I and type II diabetes. | 4 |
| Total across these question types | 20 | |
Question types and mark tariffs are Gradora’s guidance based on how this topic is typically examined — not the board’s official paper structure.