Biology HL

1. 1.

   A hypothetical team asks whether tree cover reduces heat exposure in a school courtyard. Biology members propose canopy and leaf measurements; physics members propose radiation and temperature measurements. Design four linked features of a plan that tests a shared question rather than producing disconnected subject reports.

   [4 marks] · no calculator

   Worked explanation

   1. State the common comparison in terms of measurable heat exposure rather than an unrestricted claim that trees always cool everything.
   2. Pair biological context with physical measurements at the same places and times.
   3. Document responsibilities and analysis choices; a written design is preparation, not evidence of completed teamwork.

   Common mistake: Measuring shade on one day and temperature on a very different day confounds canopy effects with weather.

   Marking points

   • Pair shaded and exposed sites with comparable surface type and measurement height.
   • Record temperature, canopy/shade and radiation at matched times with shared site identifiers.
   • Agree measurement units, calibration, repeated observations and shared metadata including weather.
   • Allocate roles and cross-checks and compare the integrated data while accounting for confounders such as wind and surface material.

   Examiner tip: Measuring shade on one day and temperature on a very different day confounds canopy effects with weather.

2. 2.

   In hypothetical pilot data, one team member records 42 C using an infrared sensor aimed at paving; another records 29 C using a shaded air-temperature probe at head height. Explain why neither result necessarily invalidates the other and propose three decisions needed for a fair comparison of shaded and unshaded sites.

   [4 marks] · no calculator

   Worked explanation

   1. Do not average temperatures of different physical targets as though they measured one variable.
   2. Select an outcome and standardize how it is collected in shaded and exposed settings.
   3. Both datasets may be useful if their distinct meanings and methods remain explicit.

   Common mistake: A numerical disagreement does not prove an instrument is broken when the sensors are measuring different targets.

   Marking points

   • The instruments measure different quantities: surface temperature versus air temperature.
   • Choose and define the heat-exposure outcome relevant to the shared research question.
   • Use matched sensor types, calibration and exposure/height rules for each comparison.
   • Synchronize repeated measurements and record weather, surface and shade metadata, retaining both original measurement types separately.

   Examiner tip: A numerical disagreement does not prove an instrument is broken when the sensors are measuring different targets.

3. 3.

   A hypothetical team has funds for either more courtyard sites or repeated measurements at existing sites. Initial data show large day-to-day variation and only two courtyard sites. Explain the value of each option, propose a justified compromise and state how the team should communicate the remaining uncertainty.

   [4 marks] · no calculator

   Worked explanation

   1. Differentiate spatial replication from repeated observations over time.
   2. Use the stated large temporal variation and small site count to justify balancing both, not declaring one universally best allocation.
   3. Document trade-offs and communicate limits instead of turning agreement within the team into evidence of certainty.

   Common mistake: Many readings from one site do not create many independent courtyard sites.

   Marking points

   • More independent sites improve representation of spatial variation and generalizability.
   • Repeated times characterize day-to-day variability and reduce reliance on one unusual day.
   • A defensible compromise samples several matched site pairs on multiple days with documented priorities rather than treating repeats at one site as independent sites.
   • Report the number of sites/days, variability, constraints and bounded conclusions, with the allocation decision recorded collaboratively.

   Examiner tip: Many readings from one site do not create many independent courtyard sites.

4. 4.

   For a hypothetical biology-physics rehearsal, each of two courtyard plots receives 600 W m^-2 solar input and reflects 150 W m^-2. A simplified agreed model assigns 300 W m^-2 to evaporation/transpiration in the vegetated plot and 50 W m^-2 in the bare plot. Neglect other fluxes for this arithmetic. Calculate the residual power available for other warming in each plot and their difference. Explain the biological link to latent heat and why these residuals alone cannot predict an air-temperature difference.

   [4 marks]

   Syllabus placement evidence: Biology subject brief, first assessment 2025, II Curriculum model overview p.2 collaborative sciences project; p.4 Inquiry process, Concluding and evaluating. A supplied energy-budget application links transpiration and physics within HL collaborative preparation. The flux model is given, not claimed as a prescribed biology equation; no real cooling result, practical participation or assessed project is asserted.

   Worked explanation

   1. Use the same input and reflected-energy boundary for both plots before subtracting the explicitly supplied evaporative term. The extra 250 W m^-2 latent allocation explains the lower vegetated residual in this model.
   2. Biology supplies a water-loss mechanism while physics accounts for energy. Converting this simplified power balance to air temperature requires further terms and measurements; the calculation is not evidence of an actual courtyard cooling effect.

   Common mistake: A power-flux difference cannot be reported as degrees of cooling without a justified thermal model and boundary conditions.

   Marking points

   • Vegetated residual=600-150-300=150 W m^-2.
   • Bare residual=600-150-50=400 W m^-2; difference=250 W m^-2.
   • Water evaporation, including transpiration through leaves, requires latent heat and can divert available energy from sensible warming.
   • Temperature also depends on heat capacity, heat transport, wind, long-wave exchange and time; a residual flux in W m^-2 is not a temperature change.

   Examiner tip: A power-flux difference cannot be reported as degrees of cooling without a justified thermal model and boundary conditions.

5. 5.

   In a hypothetical urban-heat project, shaded-site loggers recorded all ten scheduled afternoons, but exposed-site loggers failed on the four hottest afternoons according to an independent school weather record. A draft compares the ten shaded observations with the six exposed observations and claims an unbiased shade effect. Explain the missing-data risk, propose a defensible immediate comparison and a targeted collection repair, and specify how the two subject teams should document the remaining limitation.

   [4 marks] · no calculator

   Syllabus placement evidence: Biology subject brief, first assessment 2025, II Curriculum model overview p.2 collaborative sciences project; p.4 Tools/Technology and Inquiry process, Concluding and evaluating. Rehearses shared interpretation of logger failures and an explicit comparison boundary. Core HL preparation applies supplied missing-data conditions, not a required specialist statistical method, actual logger deployment or assessed collaboration.

   Worked explanation

   1. The missingness is associated with the outcome conditions, not random loss of interchangeable observations. Unequal-day means mix site and weather effects.
   2. Matching days improves the immediate comparison but does not restore the four hot days. A jointly logged equipment repair and transparent restricted claim are needed; filling gaps with chosen values would manufacture evidence.

   Common mistake: Discarding unmatched shaded days fixes temporal mismatch but does not make the remaining days representative of all heat conditions.

   Marking points

   • Exposed observations are selectively missing during heat, so the six retained values need not represent the full exposed-site temperature distribution and may understate heat exposure.
   • Compare matched site pairs on the six common afternoons as a conditional descriptive analysis, retaining the ten-day record and explicitly limiting inference to the matched subset.
   • Investigate logger operating limits/power and plan validated backup or suitable rated sensors at both sites to capture hot afternoons, without inventing missing temperatures.
   • Jointly flag failures with dates/weather and reasons, record exclusions and method changes, and state that matched-subset results cannot establish the unobserved hottest-day shade effect.

   Examiner tip: Discarding unmatched shaded days fixes temporal mismatch but does not make the remaining days representative of all heat conditions.

Original, unofficial practice questions from SubjectScout — not official past-paper questions or complete syllabus coverage. Added English teaching explanations are AI-authored; independent teacher review is pending.