What you need to know
- Unit 6Choose apparatus in enough detail to measure the variables, discuss calibrationChecking or setting a measuring instrument against a known standard, such as finding what one eyepiece division is worth. such as a zero check, and say how the data will be used.
Core Practical methods stay in their own guides. A school zero check is not a national calibration certificate. Do not invent instrument ranges the question did not need.
By the end, you should be able to…
- Give the range, resolutionThe smallest distance between two points that can still be seen as separate points. or dimensions that make a named instrument suitable.
- State a calibration or zero check that matches that instrument.
- Describe the measurement and how the readings will be processed.
Build your understanding
Detail means the instrument could be used
“Use a quadratA square frame of known area used to sample organisms.” does not say how large the sample is. Unit 6 can ask for the range and resolutionThe smallest distance between two points that can still be seen as separate points. of an instrument, or a relevant dimension. An illustrative quadrat of 0.5 m by 0.5 m has area 0.5 × 0.5 = 0.25 m². Twelve plants in that quadrat are 12 ÷ 0.25 = 48 plants per m². Dividing by the side length, 0.5 m, is the wrong area.
A balance reading to 0.01 g is the wrong choice if you must detect a change of about 0.001 g, and quoting 0.001 g from a 0.01 g balance invents resolution. A 10 cm³ syringe is a poor way to deliver 0.2 cm³ if a 1 cm³ syringe is available. Give the detail the measurement needs, then stop.
Calibration here means a check before you trust the scale
The specification’s example is whether a meter reads zero before you measure. An illustrative balance is tared with the empty boat in place. If the empty boat reads 0.20 g and you do not tare or subtract, every mass is high by 0.20 g. That is a systematic offset. Repeating the weighing repeats the offset.
A colorimeter check is a blank of the same solventA liquid in which other substances (solutes) dissolve. Water is a good solvent for ions and polar molecules. set to zero before the samples. A pHA measure of how acidic or alkaline a solution is, based on its H⁺ ion concentration. Below 7 is acidic, above 7 is alkaline. meter check is a reading against a stated buffer before the series, not a guess that the meter “looks right.” Do not describe a manufacturer’s service procedure. Say the school check the question’s apparatus allows.
Say how the data will be used
State the record before you collect it: a table of raw counts and a mean per quadrat, a rate as volume divided by time, or a graph of the dependent variable against the independent variable. If the counts are expected to multiply, say that a logarithmic axis may be used and that it must be labelled as such.
Name a statistical test in the plan only when the data match it: categories with expected counts, a comparison of means, or paired measurements. Say that a critical value would have to be supplied before any result was called significant. Do not write “the data will prove the hypothesis.”
Graph skills: SLAPUK and choosing a scalePlotting volume against time: scales for awkward values.
Make your reasoning visible
Resolution, then the digit you will record
A reading cannot honestly have more decimal places than the instrument shows. State that limit in the plan.
Zero check, then the measurement
Put the blank, tare or buffer check in the method before the first experimental reading, not as an afterthought.
Avoid this misconception
The claim: Naming a piece of glassware is a complete apparatus answer.
The correction: Add the detail that affects the result: dimensions or range, the unit, a zero or blank check, and what calculation or graph will use the numbers.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
An illustrative student counts a plant in quadrats of 50 cm by 50 cm and reports “7 per quadrat” as if it were a density in per m². What area should be used, and what is the density if one quadrat contains 7 plants?
Show suggested answer
50 cm is 0.50 m, so the area is 0.50 × 0.50 = 0.25 m². Density = 7 ÷ 0.25 = 28 plants per m². Seven per quadrat is not 7 per m².
Practice question
Retrieval and explanation · suggested answer
A balance shows 0.15 g with an empty weighing boat. The student then records the boat plus tissue as 1.20 g and calls the tissue 1.20 g. What check was missed, and what is the tissue mass?
Show suggested answer
The balance was not tared, or the boat mass was not subtracted. Tissue mass = 1.20 − 0.15 = 1.05 g. Leaving the boat in every reading would shift all masses up by 0.15 g.
Practice question
Retrieval and explanation · suggested answer
The plan will collect gas volume every minute for ten minutes. How should those data be used?
Show suggested answer
Record volume and time with units, plot volume against time, and take the rate from the gradient of a straight section using a large triangle. Do not divide the final volume by ten unless the line starts at the origin and is straight for the whole ten minutes.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
You must plan a comparison of vitamin C in two unfamiliar juices using DCPIP. Give one apparatus detail, one calibration or standardisation step, and how the titres will be used. State one assumption.
Show a hint
Transfer the titration. Do not invent a unique concentration for these juices.
Explore the reasoning
Use a burette or syringe whose resolution is fine enough for the titre, and record volume in cm³. Standardise by using the same stated volume and concentration of DCPIP for every run, and a rough titre first so the range is known. Compare the juices by the mean titre: the smaller volume of juice needed to decolourise the same DCPIP has the higher vitamin C concentration. A known ascorbic acid solution would turn titres into concentrations. The assumption is that nothing else in the juice is decolourising the DCPIP.
Recall this lesson
Lesson recall questions
Question 1 of 5: Outline, in order, how a respirometer should be calibrated and zero-checked before measuring respiratory rate of germinating seeds.
Unit 6 planning
Practice question
Retrieval and explanation · suggested answer
Outline, in order, how a respirometer should be calibrated and zero-checked before measuring respiratory rate of germinating seeds.
Lesson: P2: Apparatus, calibration and the data you will use
Build the sequence from memory first. Then reveal the model order.
Tap the steps in the order you recall. Tap a placed step to send it back.
- 01Next step
- 02Waiting
- 03Waiting
Tap to place
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
A zero check is not a standards-laboratory certificate
P2 · Apparatus, calibration and the data you will useNIST describes calibration services for people who need measurements tied to national standards. A school plan does not book that service. The exam point is the same idea…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
NIST describes calibration services for people who need measurements tied to national standards. A school plan does not book that service. The exam point is the same idea at the scale of the apparatus in front of you: check the zero, the blank or the standard before you trust the readings. Metrologists maintain chains of comparison between instruments and reference standards. Your school check is smaller, but the logic transfers: a displayed number is trustworthy only for an instrument and range that suit the quantity. Taring a balance removes one offset; it does not make a coarse balance sensitive to tiny mass changes. The choice of apparatus, zero check and units belong in the plan before data are collected.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Planning Plan an investigation: formulate a null hypothesis, identify variables, choose and calibrate apparatus, consider repeats, safety and ethics, and state how data will be used.
Use the science
Why is “the balance is accurate because it is digital” not a calibration check?
Explore a possible response
A digital display can still be offset if it was not tared, or if it was tared with the wrong container. A check is a stated action, such as setting the empty container to 0.00 g before adding the sample.
Explore the source
A chain of measurements begins with a check
P2 · Apparatus, calibration and the data you will useNIST explains measurement traceability as a chain of comparisons from an instrument to reference standards. A school practical does not need a national certificate, but it does need…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
NIST explains measurement traceability as a chain of comparisons from an instrument to reference standards. A school practical does not need a national certificate, but it does need an appropriate range, resolution and zero or blank check. A pH meter checked against a buffer answers a different question from a balance tared with an empty boat. Neither check rescues a measurement made outside the instrument’s useful range. Planning apparatus is therefore a scientific decision about what variation the instrument can resolve, not a shopping list of equipment names.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Planning Plan an investigation: formulate a null hypothesis, identify variables, choose and calibrate apparatus, consider repeats, safety and ethics, and state how data will be used.
Use the science
Why is a balance reading to 0.01 g unsuitable for detecting an expected change of 0.001 g, even after taring?
Explore a possible response
Taring checks or removes a zero offset. It does not create the finer resolution needed to distinguish a one-thousandth-gram change.