Respiratory quotient (CIE A-level biology)

This lesson describes the meaning of the respiratory quotient and guides students through the calculation of values from respiration equations. The PowerPoint and accompanying resource have been planned to cover the content of points 12.1 (5 & 6) of the CIE A-level biology specification (for assessment in 2025 - 2027).

The lesson begins with a recall challenge, where the students have to demonstrate their knowledge of ATP and relative energy values to reveal the two letters, RQ. The meaning of a quotient is provided and time allocated, where they are encouraged to discuss which two respiratory values might be used, using their brief knowledge of aerobic respiration from iGCSE. The formula is provided and then a worked example used to model the calculation. The obtained value of 1.0 is explained as the RQ if metabolism consists entirely of carbohydrates. Two exam-style questions are then used to challenge the students to apply their understanding and they’ll reveal the value of 0.7 for lipids. A quick quiz round introduces the range for amino acids as 0.8 - 0.9 before a final task gets them to obtain another value and to recognise that more than one type of molecule is often metabolised.

The lesson is full of understanding and prior knowledge checks, and the answers are embedded into the PowerPoint to allow students to assess their progress.