GCSE BIOLOGY • SKILLS MODULE

Maths & Working Scientifically

The hidden 25% of the exam. Precision in calculation and evaluation.

Mastering data, variables, and the logic of discovery.

1. Mathematics in Biology
Core Calculations:
  • Mean: Total sum / number of samples.
  • Anomaly: A result that does not fit the trend of the other results or lies far outside the range. (Always identify and exclude before calculating mean).
  • Percentage Change: $\frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100$.
Rate of Reaction:

$\text{Rate} = \frac{\text{Change in Value}}{\text{Time Taken}}$

Example: bubbles per minute, $cm^3/s$, or $1/\text{time}$.

Surface Area to Volume Ratio (SA:V)

As an organism gets larger, its SA:V ratio decreases. This explains why multicellular organisms need specialised transport systems (like lungs or gills) as diffusion across the surface is no longer sufficient.

2. Working Scientifically: Quality of Data
Repeatability vs Reproducibility:
  • Repeatable: The same person gets the same results using the same method and equipment.
  • Reproducible: A different person or different equipment/method gets the same results.
Accuracy vs Precision:
  • Accuracy: How close a measurement is to the true value.
  • Precision: How close repeated measurements are to each other (consistency).
VariableRole in Investigation
IndependentThe factor you change (e.g., Light intensity).
DependentThe factor you measure (e.g., Number of bubbles).
ControlFactors kept the same to ensure the results are valid.
3. Graph Skills: Precision & The Origin
  • SLAP-U: Scale, Line of best fit, Axes (labeled with units), Points plotted, Units.
  • The Origin Rule: Only force a line of best fit through the origin (0,0) if the relationship should logically pass through zero (e.g., if there is 0 light, there is 0 photosynthesis).
  • Line of Best Fit: Smooth curve or straight line. Circle anomalies and do not let them pull your line of best fit away from the trend.

Q: Describe vs Explain — how do you handle a graph question?

Describe: State the pattern (e.g., "As the concentration increases, the mass increases").
Explain: Use "because" (e.g., "Because water moves in by osmosis through a partially permeable membrane").
4. Evaluation & Conclusion Mastery

Evaluating the Method:

  • Resolution: Was the measuring equipment precise enough to detect small changes? (e.g., using a gas syringe instead of counting bubbles).
  • Sample Size: Is it representative? Repeat tests to identify anomalies.
  • Bias: Ensure random selection where applicable (e.g., in ecology).

Conclusion Logic:

"Correlation does not mean causation." Always check if another factor could be responsible for the observed trend.

Final Exam Guardrail

• Anomalies: Identify the anomalous result and state why it does not fit the trend before excluding it from the mean.
• Significant Figures: Match the decimal places or sig figs used in the original question data.
• Validity: If the control variables aren't mentioned, the experiment is not valid.
• Resolution: The smallest change an instrument can detect. Higher resolution = higher precision.