Required practicals checklist

You change

The specimen observed (onion epidermis or cheek cells)

You measure

The cell structures seen and their measured image size

You keep the same

The same microscope and light setting for each specimen; The same stain for each specimen of one type; Starting at the lowest-power objective each time

1. Start on the lowest-power objective, focus with the coarse then the fine focus.
2. Stain the specimen (iodine for onion, methylene blue for cheek cells) under a cover slip lowered at an angle.
3. Draw what you see with clear pencil lines, ruled labels and the magnification.

Exam trap. Magnification is not resolution: a bigger image does not show more detail. Convert mm to µm (× 1000) before dividing.

Full walkthrough of RP01: method, results and questions

You change

Concentration of the sucrose solution (mol/dm³)

You measure

Percentage change in mass of the potato cylinder

You keep the same

Length and diameter of the cylinders (same cork borer); Volume of solution in each tube; Time left in solution

1. Cut equal cylinders, blot and weigh each one.
2. Leave each in a different concentration for the same time and temperature.
3. Blot the same way, reweigh and work out the percentage change in mass.

Exam trap. Compare percentage change, not grams. Where the line crosses zero, the solution matches the cells' concentration.

Full walkthrough of RP02: method, results and questions

You change

The food sample tested

You measure

The colour change seen with each reagent

You keep the same

The volume of reagent added; The amount of food sample; The temperature and time for the Benedict's test

1. Benedict's: heat in a water bath; blue turns green, yellow or brick red for sugar.
2. Iodine: orange-brown turns blue-black for starch. Biuret: blue turns purple for protein.
3. Lipids: Sudan III gives a red layer (or the ethanol emulsion test).

Exam trap. Learn each test as reagent, method and positive colour, and do not leave out the lipid test.

Full walkthrough of RP03: method, results and questions

You change

pH of the buffer solution

You measure

Time taken for the starch to be broken down (iodine stays orange-brown)

You keep the same

Temperature (water bath at, for example, 35 °C); Volume and concentration of amylase; Volume and concentration of starch

1. Warm amylase, starch and a pH buffer separately in a water bath.
2. Mix, start timing, and test a drop on iodine every 30 seconds.
3. Stop when the iodine stays orange-brown; rate = 1000 ÷ time.

Exam trap. Keep temperature fixed so only pH changes. The true end point can be up to one sampling interval earlier.

Full walkthrough of RP04: method, results and questions

You change

Light intensity, changed by the distance of the lamp from the pondweed

You measure

Rate of photosynthesis (bubbles or volume of oxygen per minute)

You keep the same

Temperature (LED lamp or heat shield); Carbon dioxide concentration (same sodium hydrogencarbonate solution); The same piece of pondweed

1. Put pondweed in hydrogencarbonate solution with a lamp at a measured distance.
2. Let it adjust, then count bubbles (or collect gas) for a fixed time; repeat.
3. Move the lamp to new distances and keep the temperature constant.

Exam trap. Light intensity is proportional to 1/d², not 1/d. Bubbles are not all the same size.

Full walkthrough of RP05: method, results and questions

You change

The factor tested, for example drinking caffeine

You measure

Reaction time (from the distance the ruler falls, using a conversion table)

You keep the same

The same hand (dominant hand); The ruler's starting position, with zero at the top of the thumb; The same person dropping the ruler, with no warning

1. The partner drops the ruler without warning, zero level with the top of the thumb.
2. Read the distance fallen; repeat and find the mean.
3. Change one factor, repeat, and convert distance to time with a table.

Exam trap. A distance is not a time. Practice improves the second set, so use a control or randomise the order.

Full walkthrough of RP06: method, results and questions

You change

Position: random coordinates (population) or distance along a transect (distribution)

You measure

Number of the plant species in each quadrat

You keep the same

The same size of quadrat; The same way of counting plants on the edge; Sampling on the same day

1. Make a grid with tape measures and place quadrats at random coordinates.
2. Count in at least 10 quadrats; mean per m² × total area = population.
3. For distribution, place quadrats at regular intervals along a transect.

Exam trap. Throwing a quadrat is not random sampling. Random quadrats estimate population; a transect shows how numbers change.

Full walkthrough of RP07: method, results and questions

You change

(A preparation, not an investigation) the choice of insoluble base and acid

You measure

The mass and purity of dry crystals obtained

You keep the same

Adding the base until it is in excess; Not heating the solution to dryness; Drying the crystals the same way

1. Warm the dilute acid and add the insoluble base until some is left over.
2. Filter off the excess solid.
3. Evaporate some water, leave to crystallise, then dry the crystals.

Exam trap. Never heat to dryness, and filter out the excess base before crystallising.

Full walkthrough of RP08: method, results and questions

You change

The solution electrolysed (for example copper chloride, sodium chloride, copper sulfate)

You measure

The product at each electrode

You keep the same

Inert (graphite) electrodes; The same low voltage; The same concentration and volume of solution

1. Use inert (graphite) electrodes and a low voltage.
2. Collect any gas over each electrode and look for solids.
3. Test the gases: chlorine bleaches damp litmus, oxygen relights a glowing splint, hydrogen pops.

Exam trap. Say what you do and what you see in a gas test. Hydrogen, not a reactive metal, forms at the negative electrode.

Full walkthrough of RP09: method, results and questions

You change

The variable changed, for example the volume of alkali added or the mass of metal

You measure

Temperature change (highest or lowest temperature minus starting temperature)

You keep the same

Volume and concentration of the acid; Starting temperature; Insulation (polystyrene cup with a lid)

1. Measure a fixed volume of the first solution into an insulated cup and record its temperature.
2. Add the second reactant, stir, lid on, and record the highest (or lowest) temperature.
3. Repeat with different amounts and plot the temperature change.

Exam trap. Read the start temperature before mixing. The answer is a change, not the highest reading.

Full walkthrough of RP10: method, results and questions

You change

Concentration of the acid (or of sodium thiosulfate)

You measure

Volume of gas over time, or time for the cross to disappear

You keep the same

Temperature; Mass and size of marble chips (or volume of thiosulfate and total volume); Volume of acid

1. Gas method: add the chips, bung at once, read the gas volume every 10 seconds.
2. Turbidity method: time how long until the cross under the flask disappears.
3. Change the concentration, keeping total volume and temperature the same.

Exam trap. Higher concentration means more frequent collisions, not faster particles. Fitting the bung quickly reduces gas loss; it does not stop it.

Full walkthrough of RP11: method, results and questions

You change

The ink or food colouring tested

You measure

The distance moved by each spot and its Rf value

You keep the same

The same solvent; The same paper; The same starting line and spot size

1. Draw a pencil start line above the solvent and put small spots on it.
2. Stand the paper in solvent, cover, and remove it before the solvent reaches the top.
3. Mark the solvent front; Rf = distance moved by spot ÷ distance moved by solvent.

Exam trap. Measure both distances from the start line, and only compare Rf values in the same solvent.

Full walkthrough of RP12: method, results and questions

You change

The water sample (tap, rain, stream, salt water)

You measure

pH and mass of dissolved solids per unit volume

You keep the same

The same volume of each sample; The same balance and evaporating basin method; The same pH method

1. Measure the pH with a meter or universal indicator and chart.
2. Evaporate a weighed sample to find the mass of dissolved solids.
3. Distil salt water and check the distillate: pH 7, no residue, boils at 100 °C.

Exam trap. Potable is safe to drink; pure means one substance. Clear water is not proof of either.

Full walkthrough of RP13: method, results and questions

You change

Energy transferred by the heater (power × time)

You measure

Temperature of the block

You keep the same

Mass of the block; Insulation around the block; Power of the heater

1. Weigh the block, insulate it and add oil to the thermometer hole.
2. Record temperature and energy (joulemeter, or V, I and t) every minute.
3. c = energy ÷ (mass × temperature change), or use the graph's gradient.

Exam trap. Use the temperature change, not a temperature. Energy lost to the air makes c come out too high.

Full walkthrough of RP14: method, results and questions

You change

Length of wire (or the arrangement of resistors)

You measure

Resistance, from R = V ÷ I

You keep the same

Material and diameter of the wire; Temperature of the wire (small current, switch off between readings); The same meters and supply

1. Ammeter in series, voltmeter in parallel with the length of wire.
2. Read V and I for lengths from 10 to 100 cm, switching off between readings.
3. Also measure resistors in series and in parallel.

Exam trap. Keep the current small so the wire stays cool. Convert mA to A before R = V ÷ I.

Full walkthrough of RP15: method, results and questions

You change

Potential difference across the component

You measure

Current through the component

You keep the same

The component tested; Temperature of the resistor (small currents); The same meters

1. Build the circuit with the component, a series ammeter and a parallel voltmeter.
2. Vary the potential difference and record current in both directions.
3. Plot current against potential difference for a resistor, a lamp and a diode.

Exam trap. Only the resistor at constant temperature gives a straight line. The diode needs a protective resistor.

Full walkthrough of RP16: method, results and questions

You change

The object or liquid measured

You measure

Its density (mass ÷ volume)

You keep the same

The same balance, zeroed before use; Reading volumes at eye level at the bottom of the meniscus; Consistent units

1. Regular solid: measure length, width and height; volume = l × w × h.
2. Irregular solid: displacement in a eureka can or measuring cylinder.
3. Density = mass ÷ volume, with volumes read at the bottom of the meniscus.

Exam trap. 1 m³ = 1 000 000 cm³, so 1 g/cm³ = 1000 kg/m³.

Full walkthrough of RP17: method, results and questions

You change

Force (weight) on the spring

You measure

Extension of the spring

You keep the same

The same spring; Reading the length at eye level from the same point; Adding weights gently

1. Measure the unstretched length against a vertical ruler.
2. Add weights one at a time and measure the new length at eye level.
3. Plot force against extension; k is the gradient of the straight part.

Exam trap. Extension is new length minus original length. Plotted the other way round, the gradient is 1/k.

Full walkthrough of RP18: method, results and questions

You change

Resultant force (hanging weight), or the mass of the system

You measure

Acceleration, from light gates or ticker tape

You keep the same

Total mass of the system when force is varied; Force when mass is varied; The same runway, angle and light gate positions

1. Pull the trolley with a string over a pulley and a hanging mass.
2. Measure acceleration with light gates (or ticker tape).
3. To vary force, move masses from trolley to hanger so the total mass stays the same.

Exam trap. Adding new masses to the hanger changes the mass being accelerated too. a = Δv ÷ t: divide by time once.

Full walkthrough of RP19: method, results and questions

You change

None is changed on purpose: this practical measures frequency and wavelength to find the wave speed

You measure

Wavelength, and so wave speed

You keep the same

The same depth of water in the ripple tank; The same tension and length of string; Measuring across several waves

1. Ripple tank: measure across 10 wavefronts and divide by 10.
2. Count waves passing a point in 10 s for the frequency; v = f λ.
3. String: adjust the vibration generator until a steady wave forms, then measure several half wavelengths.

Exam trap. The wave carries energy along; the water and the string only move up and down. Use metres in v = f λ.

Full walkthrough of RP20: method, results and questions

You change

The type of surface (matt black, shiny black, matt white, shiny silver)

You measure

Infrared radiation emitted, measured by a detector reading

You keep the same

Distance from detector to surface; Temperature of the water in the cube; Time the reading is taken

1. Fill a Leslie cube with hot water.
2. Hold an infrared detector the same distance from each face and read it quickly.
3. Rank the surfaces; matt black emits most, shiny silver least.

Exam trap. Surfaces absorb or emit infrared radiation, not temperature. Say which one your experiment measured.

Full walkthrough of RP21: method, results and questions