Biology SL

1. 1.

   For a hypothetical team project on a river, biology students propose counting invertebrates, chemistry students propose nitrate tests and physics students propose measuring flow. Design a shared sampling plan that allows the three datasets to be interpreted together. Identify four essential coordination decisions.

   [4 marks] · no calculator

   Worked explanation

   1. Data measured at different places or after different rainfall events cannot automatically explain each other.
   2. Link organism, nutrient and flow records with shared identifiers and documented methods.
   3. Plan roles, replication and safety before collection; this written plan does not demonstrate that a team has collaborated.

   Common mistake: Three disconnected subject reports do not create an integrated investigation without comparable samples and a shared question.

   Marking points

   • Use agreed mapped sampling sites and matched dates/times so datasets refer to comparable river conditions.
   • Agree units, equipment calibration and a shared data table including site, time and method metadata.
   • Assign roles and cross-checks, with a named way to resolve missing/inconsistent records.
   • Include repeated samples and a common safety/access plan, avoiding unsupported causal conclusions from spatial correlations.

   Examiner tip: Three disconnected subject reports do not create an integrated investigation without comparable samples and a shared question.

2. 2.

   Two hypothetical team members report dissolved oxygen at the same site as 8.0 mg dm^-3 and 80% saturation. One suggests averaging the numbers to get 44. Explain why that is invalid and propose three checks before combining or comparing the results.

   [4 marks] · no calculator

   Worked explanation

   1. Unit compatibility is a prerequisite for averaging; a percentage is not a concentration in disguise.
   2. Saturation concentration depends on physical conditions, so conversion requires information beyond the two reported numbers.
   3. A shared review should resolve the mismatch transparently without overwriting inconvenient original observations.

   Common mistake: Numerical proximity or use of the same word oxygen does not make measurements dimensionally compatible.

   Marking points

   • Concentration and percentage saturation have different units/definitions and cannot be averaged directly.
   • Check temperature and pressure and use an appropriate saturation relationship if conversion is needed.
   • Check calibration, probe method and uncertainty for each measurement.
   • Check the actual sampling time, depth and location and retain original records while documenting any conversion.

   Examiner tip: Numerical proximity or use of the same word oxygen does not make measurements dimensionally compatible.

3. 3.

   A hypothetical team's two downstream samples show fewer invertebrate species than two upstream samples. The team proposes publicly blaming a named farm for pollution. Evaluate the proposed claim and give two scientifically and ethically defensible next steps.

   [4 marks] · no calculator

   Worked explanation

   1. Separate the observed species counts from an untested causal attribution.
   2. Plan more comparable evidence and appropriate access rather than treating suspicion as permission to trespass or accuse.
   3. A defensible communication explains limitations and distinguishes evidence from interpretation.

   Common mistake: An upstream-downstream association alone neither identifies a source uniquely nor justifies a public accusation.

   Marking points

   • Four samples establish only a limited pattern and may not represent the river over time.
   • Differences in habitat, flow or other discharges confound attribution to the farm.
   • Repeat matched sampling and investigate plausible alternative explanations using agreed methods and permissions.
   • Communicate the observed association and uncertainty without unsupported blame, and invite review of methods/evidence.

   Examiner tip: An upstream-downstream association alone neither identifies a source uniquely nor justifies a public accusation.

4. 4.

   For a hypothetical joint river project, a biology team counts 24 individuals of one invertebrate taxon in a total sampled bed area of 0.30 m^2 upstream and 30 individuals in 0.60 m^2 downstream. A chemistry teammate concludes the higher downstream count indicates better conditions there. Calculate densities and evaluate that conclusion. Assume equal capture efficiency solely for the calculation. Propose a shared next sampling decision that also tests a limitation of that assumption.

   [4 marks]

   Syllabus placement evidence: Biology subject brief, first assessment 2025, II Curriculum model overview p.2 collaborative sciences project; p.4 Inquiry process, Collecting and processing data. Rehearses biology-chemistry reconciliation of unequal sampling effort and coordinated follow-up. Core SL collaborative preparation only; invented counts do not demonstrate field participation, a validated bioindicator or assessed teamwork.

   Worked explanation

   1. Compare counts per common area before sharing a direction of biological change with chemistry. The downstream sample covers twice the area, so its larger count need not imply greater density.
   2. Normalisation repairs the denominator, not every ecological inference. Joint sampling should address substrate and collection efficiency so biological counts and chemical measurements can be interpreted together without declaring a single taxon a universal quality indicator.

   Common mistake: A larger raw count from a larger sampled area is not evidence of greater density or better water quality.

   Marking points

   • Upstream density=24/0.30=80 individuals m^-2.
   • Downstream density=30/0.60=50 individuals m^-2; raw counts reverse the density ordering because areas differ.
   • One taxon's density is not a general water-quality score, and differing substrate/flow or capture efficiency can alter counts.
   • Agree equal-area replicated matched-substrate sampling with shared site/time records and comparable collection effort, recording flow/substrate alongside chemical results to investigate detectability differences.

   Examiner tip: A larger raw count from a larger sampled area is not evidence of greater density or better water quality.

5. 5.

   A hypothetical biology-physics-chemistry team proposes moving the same wet net, flow meter and sample bottles between two ponds. One pond may contain an invasive aquatic organism. Design four linked decisions that allow all three disciplines to obtain comparable evidence while reducing organism transfer and documenting the plan. No organism presence is confirmed and no sampling is authorised by this exercise.

   [4 marks] · no calculator

   Syllabus placement evidence: Biology subject brief, first assessment 2025, I Aims 8-9 p.2; II Curriculum model overview collaborative sciences project p.2; III Assessment objective 4 p.4. Applies interdisciplinary communication and ethical investigation planning to a supplied transfer risk. This is SL written preparation, not a jurisdiction-specific legal protocol, confirmed invasive-species report, performed fieldwork or completed project.

   Worked explanation

   1. Transfer can occur on instruments used by any discipline, so separate subject protocols leave a shared ecological risk. A common equipment inventory identifies every wetted route before visiting either site.
   2. Dedicated gear or site-approved decontamination reduces transfer without assuming a universal treatment suitable for all organisms or sensors. Responsibilities and logs connect ethical environmental planning to interpretable data; they do not prove compliance occurred.

   Common mistake: Cleaning only the net leaves other wet instruments as transfer routes, and an unverified suspected invasive organism must not be reported as a confirmed finding.

   Marking points

   • Check landowner/site permissions and applicable local biosecurity requirements before access; do not infer that hypothetical participation authorises fieldwork.
   • Plan dedicated site-specific equipment where feasible, or an approved cleaning/decontamination and drying protocol for all wetted gear, including the flow meter, not only the biology net.
   • Keep samples contained and site-labelled; do not transfer pond water, organisms or rinse water into the other pond, using an approved disposal route.
   • Assign a cross-disciplinary equipment/biosecurity checker and log equipment IDs, cleaning, sampling times and any deviations in the common method record to preserve comparability.

   Examiner tip: Cleaning only the net leaves other wet instruments as transfer routes, and an unverified suspected invasive organism must not be reported as a confirmed finding.

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.