Respiration

Sample questions

Original practice questions written in the style of the exam.

1. Question 12 marks

   The equation shows the complete aerobic respiration of a triglyceride, tripalmitin.

   $2\,\text{C}_{51}\text{H}_{98}\text{O}_{6} + 145\,\text{O}_2 \rightarrow 102\,\text{CO}_2 + 98\,\text{H}_2\text{O}$

   Calculate the respiratory quotient (RQ) for tripalmitin and explain what an RQ of this value suggests about the substrate an organism is respiring.

   Mark scheme

   • RQ $= 102 \div 145 = 0.70$ (1)
   • An RQ of about 0.7 suggests the organism is respiring lipids (rather than carbohydrate, RQ = 1.0) (1)
2. Question 25 marks

   Explain how ATP is produced during oxidative phosphorylation.

   Mark scheme

   • Reduced NAD and reduced FAD deliver hydrogen atoms to the electron transport chain on the inner mitochondrial membrane, where they split into protons and electrons (1)
   • Electrons pass along a series of carriers in redox reactions, releasing energy (1)
   • This energy is used to pump protons (H⁺) from the matrix into the intermembrane space, creating a proton gradient (1)
   • Protons diffuse back into the matrix through ATP synthase, which catalyses ADP + Pᵢ → ATP (chemiosmosis) (1)
   • Oxygen is the final electron acceptor, combining with electrons and protons to form water (1)