Ijmb Model Questions Vol1 2020 Biology Question 4

A class investigated the effect of temperature on the rate of aerobic respiration in yeast (Saccharomyces cerevisiae) by measuring the volume of CO₂ produced in a sealed gas syringe. The experimental set‑up was as follows: - 5.0 g of active dry yeast was mixed with 50 mL of 5 % (w/v) glucose solution. - The mixture was divided equally into three 100 mL gas syringes, each fitted with a rubber stopper. - The syringes were placed in water baths maintained at 20 °C, 30 °C and 40 °C respectively. - After a 10‑minute incubation, the volume of gas displaced in each syringe was recorded as follows: • 20 °C : 12.3 mL • 30 °C : 27.8 mL • 40 °C : 45.6 mL Assume that the gas behaves ideally and that the pressure inside the syringe equals atmospheric pressure (1 atm). The temperature of the gas inside each syringe is the same as the water bath temperature (in Kelvin). The gas constant R = 0.0821 L atm mol⁻¹ K⁻¹. Answer the following: a. Calculate the rate of CO₂ production (in µmol min⁻¹) at each temperature. b. Determine the Q₁₀ temperature coefficient for the interval 20 °C to 30 °C and for 30 °C to 40 °C. (Q₁₀ = (rate₂ / rate₁)^(10/(T₂‑T₁))) c. Discuss which temperature appears optimal for yeast respiration in this experiment and give two physiological reasons why respiration declines at temperatures above the optimum.