Biology 9700/51 Oct Nov 2021 | Cambridge AS Level Past Papers With Mark Scheme

- Independent variable: temperature; dependent variable: volume of carbon dioxide produced.
- Stirring of yeast and glucose mixture: ensures uniform distribution of yeast and glucose for consistent fermentation.
- Method for maximum fermentation rate: vary temperature, measure CO2 production over time, record data, analyze results.
- Graph prediction: expected increase in CO2 production with temperature, peak at optimal temperature, decline thereafter.
- Evidence of Crabtree effect absence in C. tropicalis: lower CO2 production compared to S. cerevisiae under high glucose, no oxygen conditions.
- Limitations of sampling method: potential bias in location selection, seasonal variations, observer error in bird counts.