What you need to know
- Unit 6Comment on how an investigation could be improved, possibly with additional apparatus that reduces error.
The improvement must be realistic for a school investigation and must not change the question into a different one. Naming a more impressive instrument is not automatically an improvement.
By the end, you should be able to…
- Name the limitation in the method you were shown.
- Propose apparatus or a step that reduces that limitation.
- Reject an improvement that is vague, impossible, or changes the independent variable.
Build your understanding
Start from the error you can see
“Use better equipment” fits every practical and answers none of them. Name the weakness first. Bubble counts estimate gas production only if every bubble has the same volume. A gas syringe measures volume instead. A colour judged by eye can be read with a colorimeter and a blank, if the mixture is clear enough for a valid reading.
A water bath that drifts can be replaced by a thermostatically controlled bath whose temperature is checked with a thermometer. A gradient taken from a tiny triangle can be improved by a larger triangle on a labelled scale. Each of those sentences has a “so that”.
Extra apparatus has to be usable
Suggesting a mass spectrometer for a school colour comparison is not realistic. Suggesting three more temperatures around a possible optimum is realistic when the problem was a gap in the range. Suggesting a larger stated quadratA square frame of known area used to sample organisms., used in both areas, is realistic when the problem was a quadrat too small to contain the plants being counted.
The new apparatus must not smuggle in a second independent variable. A brighter lamp that also warms the pondweed has not isolated light unless temperature is then controlled. Say what you would keep the same.
Some improvements are procedural
Not every improvement is a new device. Random coordinates instead of choosing “typical” vegetation, a stated number of repeats, a tare before each mass, or a control tube with no organism in a respirometer are method changes. They still need the error they address.
If the question has already named an anomaly, the improvement might be the check and the repeat, not a new aim. Do not offer a statistical test as the improvement unless the weakness was that the design could not support the test the student tried to use.
Make your reasoning visible
One error, one change, one “so that”
The reason should be the error you named. A new biological aim is a different investigation.
Keep the original question
If the independent variable was light, the improved method still changes light and holds the other factors.
Avoid this misconception
The claim: The most expensive instrument is the best improvement.
The correction: The best improvement reduces the error in this method and could actually be used. A realistic school change beats a named instrument that does not measure the dependent variable.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Bubble counts were used to compare photosynthesis at five light intensities. Suggest one piece of apparatus and the error it reduces.
Show suggested answer
Collect the gas in a gas syringe over the same stated time and record the volume. That measures volume instead of assuming every bubble has the same volume. Temperature and the pondweed should stay controlled.
Practice question
Retrieval and explanation · suggested answer
A student chose quadrats by walking to plants that looked interesting. What improvement would make the comparison fairer?
Show suggested answer
Place quadrats using a stated random method, such as random coordinates, with the same quadrat area in each area. Choosing interesting plants biases the sample towards those plants.
Practice question
Retrieval and explanation · suggested answer
Why is “use a more accurate balance” a weak answer when the problem was that the empty boat was never tared?
Show suggested answer
The error is an offset from the boat, not the resolution of the balance. Taring the empty boat, or subtracting its mass, removes that offset. A finer balance that is still not tared repeats it.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
An unfamiliar respirometer gives a fluid movement even in a control tube with no organism, and the experimental tube’s soda lime is mentioned but not checked. Propose one apparatus check and one reason a repeat of the experimental tube alone would not be enough. State an assumption.
Show a hint
Separate a leak or temperature change from the organism’s gas exchange.
Explore the reasoning
Check that the apparatus is sealed and that temperature is the same for a control tube and the experimental tube, and that the soda lime is present and not exhausted if carbon dioxide is meant to be absorbed. Repeating only the experimental tube repeats any leak or temperature drift. The control shows whether the fluid moves with no organism. The assumption is that the control matches the experimental tube in volume and temperature.
Recall this lesson
Lesson recall questions
Question 1 of 5: A table of pondweed oxygen volumes is headed ‘volume (cm³)’ but the fictional values are 12.4 mm of bubble. Identify the error and amend it.
Unit 6 implementation and measurements
Practice question
Retrieval and explanation · suggested answer
A table of pondweed oxygen volumes is headed ‘volume (cm³)’ but the fictional values are 12.4 mm of bubble. Identify the error and amend it.
Lesson: I3: Improvements that reduce a named error
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
A modification should shrink a real doubt
I3 · Improvements that reduce a named errorNational statistics guidance treats uncertainty as something to be described, not decorated away. A school improvement is in the same spirit: change the step that makes the measurement…Specification Unit 6 · Implementation and measurementsRead & use the scienceClose article
Why this matters
National statistics guidance treats uncertainty as something to be described, not decorated away. A school improvement is in the same spirit: change the step that makes the measurement doubtful. Publishing more decimal places does not do that work. A useful modification names the uncertainty it attacks. A colorimeter can replace a subjective colour match; a water bath can reduce temperature drift; a sealed connection can reduce gas leakage. Each choice has limits, so ‘use better equipment’ is not an evaluation. Professional laboratories also document whether a proposed change alters the variable being investigated. An improvement that changes the biology as well as the error may answer a different question.
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 · Implementation and measurements Evaluate readings and methods: range and number of measurements, significant figures, units, inconsistent points and realistic improvements.
Use the science
Why is “record the results to more decimal places” not an improvement of a colour match made by eye?
Explore a possible response
The doubt is the subjective match, not the number of digits on the page. A colorimeter, or a clearer standard, would change the measurement. Extra digits would only look more precise.
Explore the source
- Office for National Statistics: uncertainty and how we measure itOffice for National Statistics
A blank can change an interpretation
I3 · Improvements that reduce a named errorA microbial optical-density study corrected readings against a blank before relating turbidity to viable cell counts. The blank measured background signal from the medium and vessel; without it,…Specification Unit 6 · Implementation and measurementsRead & use the scienceClose article
Why this matters
A microbial optical-density study corrected readings against a blank before relating turbidity to viable cell counts. The blank measured background signal from the medium and vessel; without it, a cloudy medium could be mistaken for more cells. This is a useful Unit 6 improvement because it targets a named bias, not simply “more repeats”. The improvement must match the actual apparatus and question: a blank may help a colorimeter or spectrophotometer but cannot fix a leaking respirometer. Good evaluation identifies the source of error before choosing a modification.
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 · Implementation and measurements Evaluate readings and methods: range and number of measurements, significant figures, units, inconsistent points and realistic improvements.
Use the science
Why will taking five more optical-density readings not remove an uncorrected cloudy-medium background?
Explore a possible response
The same background contributes to every reading. A matched blank or calibration is needed to estimate and subtract that systematic contribution.
Explore the source
- Estimating microbial population data from optical densityPeer-reviewed study (PMC)