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A2 · Practice questions · Cell signalling and blood glucose

Signal, amplify, balance.

Six original Cambridge-style questions on cell signalling and the control of blood glucose, from the steps of the cAMP cascade to interpreting a glucose tolerance graph and a biosensor reading.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

First, second, cascade.

01
Explain
[6 marks]

Describe how glucagon causes a liver cell to release glucose into the blood.

  • Glucagon binds to a specific receptor on the cell surface membrane of the liver cell, causing a conformational change in the receptor. ✓
  • The receptor activates a G protein, which activates adenylyl cyclase. ✓
  • Adenylyl cyclase converts ATP into cyclic AMP, the second messenger. ✓
  • cAMP activates protein kinase A, which starts an enzyme cascade. ✓
  • Each enzyme activates many molecules of the next by phosphorylation, amplifying the signal. ✓
  • The final enzyme, glycogen phosphorylase, is activated and breaks down glycogen to glucose, which diffuses out into the blood. ✓
02
Explain
[2 marks]

Explain why glucagon affects liver cells but not muscle cells.

  • Only liver cells have glucagon receptors on their cell surface membranes. ✓
  • Glucagon cannot enter cells, so without a receptor there is no conformational change and no cAMP cascade in muscle cells. ✓
03
Explain
[5 marks]

Explain how blood glucose concentration is returned to normal after a meal rich in carbohydrate.

  • The rise in blood glucose is detected by β cells in the islets of Langerhans, which secrete more insulin (and α cells secrete less glucagon). ✓
  • Insulin binds to receptors on muscle cells; vesicles containing GLUT4 fuse with the cell surface membrane. ✓
  • More glucose enters muscle cells by facilitated diffusion. ✓
  • In liver (and muscle) cells insulin activates enzymes for glycogenesis, converting glucose to glycogen, and increases the respiration of glucose. ✓
  • Blood glucose falls; as it returns to the set point insulin secretion decreases: negative feedback. ✓
04
Data
[3 marks]

A person drinks a glucose solution. Their blood glucose is 5.0 mmol dm−3 at the start, peaks at 8.2 mmol dm−3 after 40 minutes and is 5.4 mmol dm−3 at 120 minutes. Calculate the percentage increase at the peak and explain the fall after 40 minutes.

  • Increase = (8.2 − 5.0) ÷ 5.0 × 100 = 64 %. ✓
  • The high glucose stimulates β cells to secrete insulin. ✓
  • Insulin increases glucose uptake by muscle (GLUT4) and liver cells and its conversion to glycogen, so blood glucose falls back towards 5 mmol dm−3. ✓
05
Explain
[4 marks]

Explain the principles of a glucose test strip used on a urine sample.

  • The pad contains immobilised glucose oxidase, peroxidase and a colourless chromogen. ✓
  • Glucose oxidase catalyses the oxidation of glucose to gluconic acid, producing hydrogen peroxide. ✓
  • Peroxidase catalyses the reaction of hydrogen peroxide with the chromogen, forming a coloured compound. ✓
  • The intensity of colour depends on the glucose concentration and is compared with a colour chart after a set time. ✓
06
Analysis
[3 marks]

Suggest two advantages of a biosensor over a urine test strip for a person with diabetes who needs to decide on a dose of insulin.

  • The biosensor gives a quantitative, precise digital reading, not a colour match that is only semi-quantitative / subjective. ✓
  • It measures blood glucose now; urine glucose reflects the past few hours and only appears once blood glucose is above the renal threshold. ✓
  • So low or only slightly high blood glucose can be detected and the insulin dose adjusted accurately (any two points). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.