AQA A-Level Biology: Regulation of Blood Glucose Concentration — mark scheme explained

The question

Explain how insulin controls glucose uptake by muscle cells. [Paraphrased for study — not reproduced from any exam paper.]

Mark scheme, decoded

What each mark is really for — in plain English — and the wording trap that loses it.

• S1

  Step 1: Insulin is produced by the beta cells of the pancreas and released into the bloodstream in response to high blood glucose levels.

• S2

  Step 2: Insulin binds to receptors on the surfaces of target cells, such as muscle cells.

• S3

  Step 3: Binding of insulin to its receptor triggers a signaling cascade within the cell.

• S4

  Step 4: This signaling cascade promotes the insertion of glucose transporter proteins (GLUT4) into the cell membrane.

• S5

  Step 5: The presence of GLUT4 in the cell membrane allows glucose to enter the muscle cells more efficiently, lowering blood glucose levels.

Model answer

Worked through, with each step tagged to the mark it earns.

1. S1

   Step 1: Insulin is produced by the beta cells of the pancreas and released into the bloodstream in response to high blood glucose levels.

2. S2

   Step 2: Insulin binds to receptors on the surfaces of target cells, such as muscle cells.

3. S3

   Step 3: Binding of insulin to its receptor triggers a signaling cascade within the cell.

4. S4

   Step 4: This signaling cascade promotes the insertion of glucose transporter proteins (GLUT4) into the cell membrane.

5. S5

   Step 5: The presence of GLUT4 in the cell membrane allows glucose to enter the muscle cells more efficiently, lowering blood glucose levels.

6. 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.

Common mistakes

• Confusing the actions of insulin and glucagon. — 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. — Practice explaining how the liver performs glycogenesis, glycogenolysis, and gluconeogenesis to regulate blood glucose.
• Misunderstanding the second messenger model. — 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. — 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. — Practice explaining how physical activity increases glucose uptake by muscle cells, helping to lower blood glucose levels.
• Not providing a clear explanation of gluconeogenesis. — Practice explaining how glycerol and amino acids are converted into glucose in the liver during fasting or prolonged exercise.

Where the marks go

• Full worked solution (all marking points)5 marks

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