A-Level Biology May/June 2025 Q1(b): Explain the features of ATP that make it suitable to be the universal energy currency o…

1 answer

• ▲0
  accepted ✓

  ATP is suitable as the universal energy currency for several key reasons:

  • It is readily hydrolysed in a single-step reaction to form ADP and an inorganic phosphate (Pi). This is a simple, rapid process.
  • The hydrolysis of the terminal phosphate bond releases a small, manageable amount of energy (approximately 30.5 kJ mol⁻¹) which is sufficient to power cellular reactions without excessive heat loss.
  • The reaction is reversible, meaning ATP can be rapidly regenerated from ADP and Pi during respiration or photosynthesis. This allows for a high rate of turnover and a constant supply.
  • ATP is a small and water-soluble molecule, allowing it to diffuse quickly to any part of the cell where energy is required.

  ---

  How the marks are awarded

  • M1 — The first point correctly states that ATP is hydrolysed to ADP and inorganic phosphate (Pi).
  • M1 — The second point states that this hydrolysis reaction releases energy, and quantifies it as 30.5 kJ mol⁻¹.
  • M1 — The third point explains that the reaction is reversible and that ATP can be regenerated, mentioning the high turnover rate.
  • M1 — The fourth point correctly identifies ATP as a small and soluble molecule, linking this property to its ability to diffuse within the cell.

  Common mistakes

  • Confusing ATP with glucose by stating it stores 'large' amounts of energy; ATP's advantage is releasing small, manageable packets.
  • Simply stating 'ATP provides energy' without explaining the mechanism of hydrolysis to ADP and Pi.
  • Describing the detailed chemical structure of ATP (adenine, ribose, three phosphates) instead of explaining the features that make it a good energy currency.
  • Incorrectly stating that energy is 'created' or 'produced' by ATP, rather than being released from chemical bonds during a transfer process.

  Examiner tip: For questions asking about suitability, always link a molecule's specific properties (e.g., small, soluble, unstable bonds) directly to its biological function (e.g., transport, manageable energy release).

  ---

  AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →

  @markscheme_answers

Your answer

Sign in to answer this question.