Biology HL
Investigation Rate Models and Uncertainty
- 1.
For written investigation preparation, hypothetical oxygen volumes at 0, 20, 40 and 60 s are 0.0, 4.0, 6.0 and 7.0 cm^3. Calculate the mean rate over the first 20 s and over all 60 s. Explain why these differ and why neither automatically equals the true instantaneous rate at time zero.
[4 marks] - 2.
A hypothetical enzyme investigation runs all low-pH trials on Monday with batch A and all high-pH trials on Friday with batch B. Five readings come from the same reaction vessel in each treatment. Identify the confounding and pseudoreplication risks and propose a design that addresses both.
[4 marks] · no calculator - 3.
In a hypothetical investigation, treatment A has mean rate 1.8 with sample standard deviation 0.4 units (n=4 independent vessels), and B has mean 2.1 with standard deviation 0.5 units (n=4). Evaluate the claim that overlapping standard-deviation bars prove no treatment effect. Suggest two next steps that improve the evidence without guaranteeing a preferred result.
[4 marks] · no calculator - 4.
For written HL investigation preparation, two hypothetical enzyme preparations are measured at matched substrate concentration, pH and temperature. A produces 0.60 micromol product min^-1 using 0.20 mg total preparation protein; B produces 0.90 micromol min^-1 using 0.50 mg. Assume rates are measured in a range proportional to enzyme amount. Calculate activity per mg total protein and the percentage difference of B relative to A on this basis. Explain why the raw rate and normalised rate rank differently, and why neither alone establishes a difference in intrinsic catalytic activity of the enzyme molecules.
[5 marks] - 5.
A hypothetical written enzyme investigation reports A=2.00 rate units at 20 degrees C and B=3.00 at 25 degrees C. For a sensitivity exercise only, assume both preparations obey the supplied exponential temperature model r(T)=r(20)*Q10^((T-20)/10), with Q10=2 and no other temperature effects across this range. Convert B to a model-equivalent rate at 20 degrees C and compare it with A as a percentage. Repeat the comparison using Q10=1.5. Explain what these calculations imply for a claim that B has a temperature-independent advantage, and propose a stronger comparison.
[5 marks]