# Yeast can respire anaerobically. Explain why yeast respiration slows down and eventually stops when the temperature rises above 35 °C.

> Cambridge International IGCSE Biology (0610) — 12.1 Respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. Respiration in yeast is catalysed by enzymes
2. High temperatures above the optimum cause the enzymes to denature
3. The shape of the active site changes / is permanently altered
4. Therefore the rate of respiration decreases / stops as the reactions can no longer be catalysed

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