What practical techniques must I master for the Eduqas Practical Endorsement and the written papers?
The Practical Endorsement: the specified practicals and core techniques (microscopy, the biochemical tests, enzyme and membrane investigations, dissection, sampling and respirometry); and how practical skills are assessed on paper.
A focused answer to the practical-skills requirements of Eduqas A-Level Biology. Covers the Practical Endorsement, the specified practicals and core techniques (microscopy, food tests, enzyme and membrane investigations, dissection, sampling and respirometry), and how practical skills are tested on paper.
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What this dot point is asking
Eduqas requires hands-on competence, assessed by the Practical Endorsement, and tests the methods and analysis of practical work on the written papers. You should be able to plan, carry out, analyse and evaluate the specified practicals. This page covers the core techniques and how they are examined.
The Practical Endorsement
Core techniques
The specified practicals develop a set of recurring techniques:
- Microscopy and calibration: using a light microscope, preparing slides, and calibrating an eyepiece graticule against a stage micrometer to measure real sizes.
- The biochemical food tests: Benedict's (reducing sugars), the hydrolysis route (non-reducing sugars), iodine (starch), biuret (proteins) and the emulsion test (lipids).
- Enzyme investigations: measuring the effect of temperature, pH, substrate or enzyme concentration on reaction rate, controlling other variables.
- Membrane permeability: for example measuring pigment loss from beetroot at different temperatures or solvent concentrations.
- Dissection: of organs (for example a heart or kidney) to relate structure to function.
- Sampling: using quadrats and transects to estimate abundance and distribution.
- Respirometry: using a respirometer to measure the rate of oxygen uptake.
How practical skills are examined on paper
About 15 percent of the written-exam marks assess practical skills. Expect to: identify the independent, dependent and control variables; explain how to make a test valid (fair) and reliable (repeated); suggest improvements; identify anomalies; and analyse and interpret practical data (graphs, tables and calculations). You may also be asked to describe a method, evaluate a given method, or justify the apparatus chosen.
Examples in context
Example 1. Why a control matters in the beetroot membrane practical. A control with no treatment (or distilled water) shows the baseline pigment loss, so any extra loss can be attributed to the temperature or solvent being tested, a key part of valid experimental design.
Example 2. Respirometry and the soda lime trap. A respirometer uses soda lime to absorb carbon dioxide so that any change in gas volume is due to oxygen uptake, illustrating how apparatus is chosen to isolate the variable being measured.
Try this
Q1. State what grades are possible for the Practical Endorsement. [1 mark]
- Cue. Pass or Not classified (it is not graded numerically).
Q2. Explain the difference between a valid and a reliable experiment. [2 marks]
- Cue. Valid means a fair test that measures what is intended (controlling variables); reliable means consistent, repeatable results (repeats and a mean).
Q3. Describe how to calibrate an eyepiece graticule. [2 marks]
- Cue. Line up the graticule against a stage micrometer of known scale at the chosen magnification, and work out how many micrometres each graticule division represents.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20195 marksA student investigated the effect of temperature on the rate of an enzyme-controlled reaction. Describe how they could obtain valid and reliable results, including the variables they should control.Show worked answer →
Use a water bath to set and maintain each temperature (the independent variable), and measure the rate by timing a clear end point (for example the time for a colour change or volume of product collected).
Control variables to make it a fair test: the same enzyme concentration, the same substrate concentration and volume, the same pH (use a buffer), and the same volumes throughout.
Repeat each temperature at least three times and calculate a mean to improve reliability and to identify anomalies.
Use a suitable range of temperatures with sensible intervals, and use appropriate apparatus to measure volumes and time accurately.
Markers reward controlling named variables (enzyme and substrate concentration, pH, volume), a valid measure of rate, and repeats with a mean for reliability.
Eduqas 20214 marksDescribe how you would use a light microscope and a graticule to measure the actual size of a cell, including how to calibrate the graticule.Show worked answer →
Place the eyepiece graticule (a scale in the eyepiece) and line it up against a stage micrometer (a slide of known scale) at the chosen magnification.
Work out how many micrometres each graticule division represents by comparing the two scales (calibration).
Remove the stage micrometer, place the specimen, and measure how many graticule divisions the cell spans.
Multiply the number of divisions by the value of one division to get the actual size; recalibrate if the magnification is changed.
Markers reward calibrating the graticule against a stage micrometer, finding the value of one division, measuring the cell in divisions, and converting to a real size (and recalibrating if magnification changes).
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Sources & how we know this
- Eduqas A Level Biology Specification (A400) — Eduqas (2015)