A-level BiologyAQA 7402

A-level Biology required practicals checklist

Tick the practicals you have revised
  • AT a, AT b, AT c, AT f, AT l · variables and method
    Change
    Temperature, pH, or the concentration of enzyme or substrate (one of them)
    Measure
    Initial rate: the gradient of product (or substrate) against time at the start, or 1 ÷ time for a colour change
    Keep the same
    The other three of temperature, pH and the two concentrations; volumes; the enzyme source
    Method
    Keep the other variables fixed with a water bath, buffer and measured volumes; record product formed or substrate left against time; repeat each value.
    Where marks go
    Measuring rate from the final plateau instead of the initial gradient; no control of pH or temperature; confusing the dependent and independent variables.

    WalkthroughsThe unit's lessonContent 3.1.4.2

  • AT d, AT e, AT f · variables and method
    Change
    Nothing: an observation and count
    Measure
    Cells in each stage of the cell cycle in a field of view; mitotic index = cells in mitosis ÷ total cells
    Keep the same
    The stain, the time in acid, the region of root tip (the first 1 to 2 mm) and how fields of view are chosen
    Method
    Hydrolyse the tip in warm acid, stain, squash gently under a coverslip, count cells in each stage across several fields of view, calibrate the eyepiece graticule.
    Where marks go
    Counting the same field twice; using the unstained or overlapping region; forgetting to calibrate the graticule for each objective.

    WalkthroughsThe unit's lessonContent 3.2.2

  • AT c, AT h, AT j, AT l · variables and method
    Change
    Concentration of the solute (sucrose or salt) in the solution
    Measure
    Percentage change in mass (or length) of the plant tissue; the concentration where it is zero
    Keep the same
    Tissue source, size and surface area of the pieces, time in solution, temperature, how pieces are blotted
    Method
    Serial or simple dilution from a stock; cut equal tissue pieces, blot and weigh before and after immersion; plot percentage change in mass against concentration.
    Where marks go
    Plotting absolute rather than percentage change; not blotting consistently; reading the intercept without explaining what zero change means.

    WalkthroughsThe unit's lessonContent 3.2.3

  • AT a, AT b, AT c, AT j, AT l · variables and method
    Change
    Temperature, or the concentration of a solvent such as ethanol
    Measure
    Absorbance (or transmission) of the solution around the tissue, with a colorimeter
    Keep the same
    Size and number of pieces, rinsing beforehand, volume of liquid, time, colorimeter filter
    Method
    Equal beetroot discs rinsed of surface pigment, a fixed volume of water at each condition for a fixed time, colorimeter absorbance of the surrounding liquid.
    Where marks go
    Not rinsing cut discs; unequal disc surface areas; claiming the pigment is produced rather than leaked.

    WalkthroughsThe unit's lessonContent 3.2.3

  • AT e, AT h, AT j · variables and method
    Change
    Nothing: a dissection
    Measure
    Observations and an annotated drawing of the structures, with their functions
    Keep the same
    Safe technique: cut away from the body on a board, handle sharp tools carefully, wash hands; ethical sourcing
    Method
    Follow the safety and ethics rules, identify and draw the structures, trace the path of air or blood, and relate structure to function.
    Where marks go
    Drawings shaded or sketchy instead of clear lines; no scale or magnification; confusing left and right sides of the heart.

    WalkthroughsThe unit's lessonContent 3.3.4.1

  • AT c, AT i · variables and method
    Change
    The antimicrobial substance, or its concentration
    Measure
    Diameter of the clear zone, then its area (πr²) minus the area of the disc
    Keep the same
    Volume and concentration of the culture, agar depth, disc size and soaking time, incubation temperature and time
    Method
    Sterilise equipment, flame the neck of the culture bottle, spread a lawn, place discs soaked in each substance and a control disc, tape and incubate at no more than 25 °C.
    Where marks go
    Sealing the plate completely; incubating at 37 °C in a school laboratory; measuring diameter as radius.

    WalkthroughsThe unit's lessonContent 3.4.4

  • AT b, AT c, AT g · variables and method
    Change
    Nothing: a separation
    Measure
    Distance moved by each pigment and by the solvent front; Rf = pigment distance ÷ solvent distance
    Keep the same
    Solvent, paper, size and concentration of the spot, and the covered tank
    Method
    Extract pigments with a solvent, spot repeatedly on a pencil line, run the solvent up in a closed container, mark the solvent front at once.
    Where marks go
    Drawing the origin in ink; letting the spot dip into the solvent; measuring Rf to the end rather than the centre of the spot.

    WalkthroughsThe unit's lessonContent 3.5.1

  • AT a, AT b, AT c · variables and method
    Change
    A factor such as light intensity (distance from the lamp), temperature or light colour
    Measure
    Time for DCPIP to lose its blue colour, or its absorbance, as a measure of dehydrogenase activity
    Keep the same
    Volume and concentration of chloroplast extract and of DCPIP, temperature, time; a tube kept in the dark
    Method
    Isolate chloroplasts in cold, isotonic buffer; add DCPIP as an electron acceptor; measure the rate of decolourisation with a colorimeter under different conditions.
    Where marks go
    Explaining the colour change as oxygen production; letting the extract warm up; no dark control.

    WalkthroughsThe unit's lessonContent 3.5.1

  • AT a, AT b, AT c, AT i · variables and method
    Change
    Temperature, or the respiratory substrate or its concentration
    Measure
    Rate of oxygen uptake (a respirometer) or of carbon dioxide release, or time for methylene blue to decolourise
    Keep the same
    Volume and concentration of the yeast culture, substrate concentration, time to equilibrate
    Method
    Yeast in buffered glucose at controlled temperatures; measure carbon dioxide or oxygen change with a respirometer or a redox indicator; equilibrate first.
    Where marks go
    Not equilibrating the apparatus; leaks in the respirometer; forgetting the carbon dioxide absorber when measuring oxygen uptake.

    WalkthroughsThe unit's lessonContent 3.5.2

  • AT h · variables and method
    Change
    One condition in a choice chamber or maze, such as humidity or light
    Measure
    Number of animals on each side after a set time, or the direction and speed of movement
    Keep the same
    Species and number of animals, time allowed, temperature; gentle handling and return of the animals
    Method
    Set up the chamber with one variable changed (humidity, light), release animals in the centre, count on each side at intervals; return animals unharmed.
    Where marks go
    Changing two variables at once; handling the animals roughly; concluding taxis from data that show only a change in speed or turning.

    WalkthroughsThe unit's lessonContent 3.6.1.1

  • AT b, AT c, AT f · variables and method
    Change
    Known glucose concentrations, to make a calibration curve
    Measure
    Absorbance (or transmission) after heating with Benedict's reagent and removing the precipitate
    Keep the same
    Volume of Benedict's reagent and of sample, heating time and temperature, colorimeter filter, dilution of the unknown
    Method
    Dilute a stock to known concentrations, carry out Benedict's or a glucose test strip or enzyme method identically for each, read absorbance, draw a calibration curve.
    Where marks go
    Extrapolating beyond the calibration range; different heating times for different tubes; no blank to zero the colorimeter.

    WalkthroughsThe unit's lessonContent 3.6.4.2

  • AT a, AT b, AT h, AT k, AT l · variables and method
    Change
    The environmental factor studied, such as light intensity or distance along a transect
    Measure
    Abundance: percentage cover, frequency or density of the species in quadrats
    Keep the same
    Quadrat size, how cover is estimated, sampling method (random or systematic), time of day and season
    Method
    Random quadrats or a belt transect across the factor's gradient; measure the factor with a measuring instrument or probe at each point; estimate cover or frequency.
    Where marks go
    Choosing quadrat positions by eye; too few samples along the gradient; concluding causation from a correlation.

    WalkthroughsThe unit's lessonContent 3.7.4

AQA A-level Biology 7402

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Questions people ask

How many required practicals are there in AQA A-level Biology?

Twelve, from enzyme rates (1) and mitosis in a root tip (2) to the distribution of a species (12). All students must carry them out.

Are the required practicals examined?

Yes. The written papers can ask about the methods, data and errors of any required practical, and at least 15% of the marks assess practical skills.

What is the practical endorsement?

A separate pass or not-classified result reported with your A-level. Your teacher awards it after watching you work in practical lessons; it does not change your grade.

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How we work this out

What it does

All 12 AQA required practicals with their apparatus codes, what each changes, measures and keeps the same. Tick them off as you revise; your ticks stay on this device.

The 12 required practical activities in AQA's A-level Biology specification (7402), the apparatus and technique (AT) codes the course maps to each, a short method, and what each practical changes, measures and keeps the same.

Method

  1. The list of practicals comes from AQA's specification. The AT codes, methods and variables are our summaries, checked against the course's own practical walkthroughs.
  2. Your ticks are kept only in this browser, and in the link if you share it. Nothing is sent to us.
  3. The next practical suggested is the one you have not ticked that would cover the most AT codes you have not yet covered; ties go to the lower number.

Independent practice for AQA A-level Biology (7402), not endorsed by AQA.

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