Biology SL
Investigation Design and Evidence
- 1.
Prepare a research question and method outline for how sucrose concentration affects potato-cylinder mass change over 60 minutes at 20 C. Give an operational research question, a measurable response, one important control and one safety or environmental precaution. This is planning only.
[4 marks] · no calculator - 2.
Hypothetical potato cylinders in one treatment change from 2.00 to 2.20 g, 2.50 to 2.70 g and 3.00 to 3.30 g. Calculate each percentage mass change and their mean. Explain why taking three balance readings of just one cylinder would not provide the same biological replication.
[4 marks] - 3.
A hypothetical student weighs wet potato cylinders immediately after removal, uses only one cylinder per concentration, and concludes that the concentration with zero measured mass change is the exact cell-sap concentration. Identify two methodological limitations with matched improvements and evaluate the exactness of the conclusion.
[5 marks] · no calculator - 4.
For written investigation preparation, a student proposes using time for leaf disks to float as an indicator of photosynthesis under different light intensities. Some disks already float before illumination because air remains inside them. Explain how this affects the endpoint, propose a standardisation step and a relevant control, and describe one reason flotation time is not a direct measurement of gross photosynthetic rate. Do not perform the procedure.
[4 marks] · no calculator - 5.
In hypothetical germination data for written investigation preparation, 20 seeds are allocated to each of two treatments. Treatment A has 18 germinated seeds with mean root length 12 mm among those germinated; B has 12 germinated seeds with mean 15 mm among those germinated. Calculate germination percentages and mean root length per originally allocated seed if ungerminated seeds are assigned zero by a stated composite-endpoint rule. Evaluate the claim that B is simply 'better for growth', and state what should be predefined in a follow-up plan.
[5 marks] - 6.
For written investigation preparation, a potato cylinder has initial mass 2.00 g and final mass 2.04 g. Each balance reading has a stated absolute uncertainty of +/-0.01 g. For this task use the conservative rule that absolute uncertainties add when two readings are subtracted. Calculate the mass gain and its absolute uncertainty, then express that uncertainty as a percentage of the mass gain. Explain why a small percentage increase in the cylinder's mass is not the same quantity as a small percentage uncertainty in its gain. These are hypothetical readings, not a performed experiment.
[4 marks]