WBI13 Practical Skills in Biology I

Lessons in WBI13

1. The Unit 3 paper: what is assessed and how
   50 marks, 80 minutes, all on CP1 to CP9, the recommended additional practicals and new contexts. Planning, measuring and processing skills; follow the command w
2. Variables, controls and fair tests
   IV changed, DV measured, controlled variables kept constant (say how). A control is a separate set-up without the IV, giving a baseline. Choose controlled varia
3. Choosing apparatus and measuring correctly
   Choose instruments with suitable resolution (pipette or burette over measuring cylinder, colorimeter over eye). Read meniscus at eye level, zero balances and co
4. Hazards, risks and safety precautions
   Hazard = what can harm; risk = the chance and type of harm; precaution = what reduces it, with a reason. In microbiology use aseptic technique, partial taping a
5. Measurement uncertainty and percentage error
   Uncertainty: half the smallest division (analogue), the last digit (digital), doubled for a difference of two readings. % uncertainty = uncertainty / value x 10
6. Significant figures, standard form and units
   Count s.f. from the first non-zero digit; match the least precise data; same d.p. down a column; round only at the end. Standard form a x 10ⁿ. 1 mm = 1000 µm, 1
7. Core calculations: means, percentage change, rates and ratios
   Mean = sum ÷ number (leave out checked anomalies). % change = (final - initial) / initial x 100. Rate = change ÷ time or 1 / time. Magnification = image ÷ actua
8. Recording results in tables
   IV first column, DV next; units in headings with a solidus; repeats then mean; same decimal places in a column; raw data separate from calculated values.
9. Choosing and plotting graphs
   Continuous IV: line or scatter graph; categoric IV: bar chart (y from zero); histogram for frequencies. IV on x, labels with units, linear easy scales filling t
10. Gradients, intercepts and rates from graphs
    Gradient = Δy ÷ Δx from a large triangle, with units and sign. Initial rate = gradient of a tangent at t = 0. Intercepts give values such as the water potential
11. Variability: range, standard deviation and error bars
    Range = max - min. s = √[Σ(x - x̄)² / (n - 1)]. Small s = repeatable data. Overlapping ±1 s error bars suggest a difference may be due to chance; a statistical
12. Conclusions, evaluation and improvements
    Conclusion: trend + data with units + biology + how far it supports the hypothesis. Evaluation: name each limitation and why it matters (no repeats, no control,
13. Planning an investigation: the 6-mark method
    Plan: IV values and how made; DV and how measured; relevant controlled variables and how; repeats with means and SDs; control; how data are used; safety. Be spe
14. Skills applied: CP1 sugars and starch, CP2 vitamin C
    CP1: colour standards or a colorimeter calibration curve make Benedict's semi-quantitative. CP2: mass of vitamin C per cm³ DCPIP from the standard, then juice c
15. Skills applied: CP3 membrane permeability, CP4 enzyme rates
    CP3: rinse, equal pieces, absorbance measures pigment leakage; denaturation and fluidity raise permeability. CP4: initial rate from a tangent or 1 / time; buffe
16. Skills applied: microscopy, graticules and mitotic index (CP5, CP6, CP7)
    Calibrate the eyepiece graticule with a stage micrometer for each objective: 1 epu = stage length ÷ epu. Mitotic index = cells in mitosis ÷ total x 100. Drawing
17. Skills applied: CP8 fibre strength, CP9 antimicrobial plants
    CP8: add small masses until the fibre breaks; force = mass x 9.81; standardise length and extraction; eye protection and a sand tray. CP9: discs in ethanol extr
18. Recommended additional practicals: heart dissection, water potential, pollen tubes
    Heart dissection: know chambers, vessels, valves and cords; label cut surfaces; risk and ethics. Water potential: percentage change in mass vs concentration, re
19. Recommended additional practical: plant mineral deficiencies
    Nitrate: amino acids, nucleotides, chlorophyll. Magnesium: chlorophyll (yellow leaves). Calcium: calcium pectate in the middle lamella (poor growth of young tis

Next exams for WBI13

• January 2027: Thu 14 Jan 2027, morning, 1h 20m
• Summer 2027: Thu 20 May 2027, afternoon, 1h 20m

From Pearson's final timetables. All exam dates. Always confirm your entries with your exams officer.