OCR GCSE Biology 2026 – 400 Free Practice Questions to Pass the Exam

Anaerobic respiration in yeast cells occurs when oxygen is not available, allowing the yeast to break down glucose through a different pathway than aerobic respiration. In this process, the primary products generated are carbon dioxide and ethanol.

The glucose molecules are converted into energy, with carbon dioxide being released as a byproduct, which is why fermentation in yeast is associated with the production of bubbles (from the carbon dioxide). The ethanol produced is also a valuable product in various applications, including in brewing and baking.

Understanding this metabolic process is essential, as it highlights how yeast can thrive in low-oxygen environments and contributes significantly to industries such as food and beverage. The other options list products that are not characteristic of anaerobic respiration in yeast, providing clarity on why only the combination of carbon dioxide and ethanol defines this specific pathway.