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The mean rate of carbon dioxide production of two types of yeast was measured at 30 °C in the same glucose solution.
| Yeast strain | Mean CO₂ produced / cm³ min⁻¹ | Standard deviation |
|---|---|---|
| Strain 1 | 4.5 | 0.3 |
| Strain 2 | 6.0 | 0.4 |
Calculate the percentage increase in the mean rate of carbon dioxide production of strain 2 compared with strain 1.
The error bars for the two strains, drawn at one standard deviation, do not overlap. Explain what this suggests about the difference between the two strains.
Suggest one variable, other than temperature and glucose concentration, that must be kept the same to make this comparison valid.