Cold-blooded animals, such as lizards, rely on their surroundings to warm their bodies. A lizard basking in the sun has a higher body temperature than one resting in the shade. Explain why the lizard basking in the sun is able to digest its food more quickly, using ideas about the Maxwell-Boltzmann distribution and activation energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cold-blooded animals cannot generate their own body heat. The rate at which they digest food depends on the rate of enzyme-controlled chemical reactions inside their bodies.
Model answer (5 marks)
At a higher body temperature the molecules in the lizard’s body have more kinetic energy, so they move faster.
The Maxwell–Boltzmann distribution of molecular energies shifts to the right as temperature rises; the peak of the distribution moves to a higher energy.
Consequently a larger proportion of the molecules possess an energy equal to or greater than the activation energy of the enzyme‑catalysed reactions.
With more molecules above the activation energy, there are more successful or effective collisions per unit time.
Therefore the rate of the digestion reactions is higher and the lizard can break down its food more quickly.
The Maxwell–Boltzmann distribution of molecular energies shifts to the right as temperature rises; the peak of the distribution moves to a higher energy.
Consequently a larger proportion of the molecules possess an energy equal to or greater than the activation energy of the enzyme‑catalysed reactions.
With more molecules above the activation energy, there are more successful or effective collisions per unit time.
Therefore the rate of the digestion reactions is higher and the lizard can break down its food more quickly.
Examiner tips
- Use the phrase ‘shift to the right’ for the Maxwell–Boltzmann distribution. Mention ‘activation energy’ and ‘effective collisions’. Show the logical chain: higher T → more kinetic energy → shift right → more molecules ≥ Ea → more effective collisions → higher reaction rate.
- common_mistakes
- :
- Confusing ‘higher temperature’ with ‘higher pressure’. Using ‘more collisions’ without linking to activation energy. Omitting the Maxwell–Boltzmann shift or activation energy concept.
Mark scheme (5 marks)
- At higher temperature, particles (molecules) have more kinetic energy / move faster
- The Maxwell-Boltzmann distribution shifts to the right / peak moves to higher energy at higher temperature
- A greater proportion / more particles have energy equal to or greater than the activation energy
- There are more successful / effective collisions per unit time
- Therefore the rate of the digestion reactions is greater / food is broken down more quickly
Key terms in this question
Maxwell-Boltzmann distribution · activation energy
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Rates and the Maxwell-Boltzmann distribution questions
- Explain how increasing the temperature of a reaction increases the rate of react…
- A student investigates the decomposition of hydrogen peroxide solution at two di…
- A student notices that a packet of crisps contains a small sachet labelled 'keep…
- A food manufacturer stores freshly pressed fruit juice in a cold warehouse at 2 …