Unit 6 biology.
Out in the world.
From field quadrats and microbial cultures to clinical measurements and research data. See why practical choices matter when science leaves the classroom.
Follow your curiosity
Choose a theme or explore the whole collection. Open a card, try its question, then compare your reasoning with a possible response. Nothing is submitted or saved.
36 articles across Unit 6. An article can belong to more than one theme.
The same four factors, at field scale
CP10 · Factors Affecting the Rate of PhotosynthesisNASA maps chlorophyll in ocean water from the colour of reflected light. The observation connects the pigment biology of photosynthesis to a global research question, but it is…Specification 5.8Read & use the scienceClose article
Why this matters
NASA maps chlorophyll in ocean water from the colour of reflected light. The observation connects the pigment biology of photosynthesis to a global research question, but it is not a direct rate measurement. In Core Practical 10, an aquatic plant gives an observable gas or bubble-rate proxy while you vary light, carbon dioxide or temperature. The interesting difference is what each instrument actually measures. The school plant gives a gas-volume or bubble-rate proxy over minutes; an orbiting sensor estimates pigment from reflected light over kilometres. Neither directly counts every molecule of glucose made. Ocean scientists must separate biological variation from clouds, suspended sediment and changing water depth before calling a colour pattern a change in production.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.8 Core Practical 10: investigate how light intensity, wavelength, temperature and carbon dioxide availability affect photosynthesis in an aquatic plant.
Use the science
Why might a bright, cold day still give a low aquatic-plant rate in the lab even though a satellite map looks green?
Explore a possible response
The map shows pigment, not instantaneous rate. In the tube, low temperature can limit Calvin-cycle enzymes even when chlorophyll and light are present.
Explore the source
Go to the lesson: Factors Affecting the Rate of Photosynthesis →An ocean-colour map needs a water sample
CP10 · Factors Affecting the Rate of PhotosynthesisNASA's PACE mission measures ocean colour to estimate chlorophyll in surface waters. Phytoplankton pigments absorb and scatter different wavelengths, so their abundance changes the light a satellite receives.…Specification 5.8Read & use the scienceClose article
Why this matters
NASA's PACE mission measures ocean colour to estimate chlorophyll in surface waters. Phytoplankton pigments absorb and scatter different wavelengths, so their abundance changes the light a satellite receives. This extends Core Practical 10's question about light wavelength and photosynthesis, but the instrument is measuring an optical proxy, not oxygen bubbles or instantaneous carbon fixation. Scientists compare satellite results with water samples because sediment, dissolved matter and mixed communities can affect colour. A strong investigation states what the sensor measures before using it to infer a biological rate.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.8 Core Practical 10: investigate how light intensity, wavelength, temperature and carbon dioxide availability affect photosynthesis in an aquatic plant.
Use the science
If two sea areas have equal estimated chlorophyll but different oxygen production, why is the satellite map not necessarily wrong?
Explore a possible response
Chlorophyll estimates pigment or biomass, whereas oxygen production is a rate. Light, nutrients, depth or temperature can change photosynthetic rate without an equal change in pigment.
Explore the source
Go to the lesson: Factors Affecting the Rate of Photosynthesis →Interrupted belts
CP11 · The Ecology of a HabitatFSC transect guidance notes that a long continuous belt can be impractical, and that several quadrats at each station along an interrupted belt give a better local picture.…Specification 5.14Read & use the scienceClose article
Why this matters
FSC transect guidance notes that a long continuous belt can be impractical, and that several quadrats at each station along an interrupted belt give a better local picture. That is evaluation of method, which 5.14 expects. Copy the idea, not someone else’s station list. Field ecologists have to decide whether a regular transect represents a habitat or merely misses small patches. Several quadrats at each station estimate local variation; they do not turn deliberately chosen stations into a random sample. Record where the belt runs and why. A later team cannot test your interpretation if your positions, quadrat dimensions and sampling rule have vanished from the notebook.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.14 Core Practical 11: study a habitat with quadrats and transects to determine distribution and abundance and measure suitable abiotic factors.
Use the science
Why might stations every 30 m miss a narrow wet flush?
Explore a possible response
A narrow habitat patch can fall between stations. You would note it qualitatively or add a targeted extra station, and say that the regular spacing under-sampled that microhabitat.
Explore the source
- Field Studies Council: transectsField Studies Council
The countryside is sampled, not counted plant by plant
CP11 · The Ecology of a HabitatThe UK Centre for Ecology & Hydrology surveys vegetation and soils in selected one-kilometre squares, recording plants in several quadrats within each square. Field teams repeat the survey…Specification 5.14Read & use the scienceClose article
Why this matters
The UK Centre for Ecology & Hydrology surveys vegetation and soils in selected one-kilometre squares, recording plants in several quadrats within each square. Field teams repeat the survey over years to detect changes in habitats. That is Core Practical 11 at a much larger scale: quadrat area, placement and repeated sampling determine what the counts can represent. The national programme uses a stratified design, so its estimates require attention to which landscape types were sampled. One interesting patch, however carefully counted, cannot stand for every habitat in a country.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.14 Core Practical 11: study a habitat with quadrats and transects to determine distribution and abundance and measure suitable abiotic factors.
Use the science
Why would five quadrats placed beside the prettiest flowers give a poor estimate of the whole square?
Explore a possible response
The placements are biased toward flower-rich patches. A defined sampling design spreads quadrats across the target area or its habitat strata, so the estimate is not driven by the observer’s preference.
Explore the source
- UK-SCAPE Countryside SurveyUK Centre for Ecology & Hydrology
Temperature is a development cue in the real calendar too
CP12 · Temperature and the Development of OrganismsNASA uses phenology, the timing of seasonal events, to study when plants green up and organisms develop. Core Practical 12 isolates temperature in a small living system. The…Specification 5.22 · 5.21Read & use the scienceClose article
Why this matters
NASA uses phenology, the timing of seasonal events, to study when plants green up and organisms develop. Core Practical 12 isolates temperature in a small living system. The link to a changing season is useful, but a satellite green-up map is not a brine-shrimp hatch count and a lab rate is not a climate forecast. A controlled incubation helps isolate temperature, but a landscape is exposed to changing temperature, light and moisture at once. An apparent early spring in a satellite image may mean earlier leaves, a different species mix or a change in visibility. A developmental rate measured in one dish cannot simply be multiplied by a constant to forecast a whole ecosystem. The organism and measured stage must be named.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.22 Core Practical 12: investigate how temperature affects organism development, taking account of ethical use.
- 5.21 Understand how temperature affects enzyme activity and organisms, including Q10.
Use the science
Why might a neat lab Q10 of 2 fail to predict this year’s insect hatch in a wood?
Explore a possible response
Field temperature fluctuates, moisture and photoperiod also cue development, and enzymes are not the only limit. The practical isolates one factor; the habitat does not.
Explore the source
Go to the lesson: Temperature and the Development of Organisms →A calendar observation can become climate data
CP12 · Temperature and the Development of OrganismsThe USGS describes Nature’s Notebook, a programme in which observers record whether seasonal events such as leaf-out or flowering are occurring. A consistent yes-or-no rule lets many people…Specification 5.22 · 5.21Read & use the scienceClose article
Why this matters
The USGS describes Nature’s Notebook, a programme in which observers record whether seasonal events such as leaf-out or flowering are occurring. A consistent yes-or-no rule lets many people make comparable records across sites and years. Core Practical 12 similarly needs a defined developmental endpoint, not an impression that one organism “looks more grown”. Temperature can affect development, but outdoors photoperiod, rainfall and species identity also vary. A long series can reveal a pattern; it does not prove that temperature alone caused every change in timing.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 5.22 Core Practical 12: investigate how temperature affects organism development, taking account of ethical use.
- 5.21 Understand how temperature affects enzyme activity and organisms, including Q10.
Use the science
Why is a daily record of “visible first leaf: yes or no” more useful than “the plant looks springlike”?
Explore a possible response
The first rule defines an observable stage that different people can apply repeatedly. The second is subjective and may mean different things at different sites.
Explore the source
- Nature’s Notebook: recording seasonal activityU.S. Geological Survey
Safe organism, then a measurement
CP13 · Growth of Microorganisms in Liquid CultureThe Microbiology Society’s case for laboratory microbiology still assumes you know what you inoculated. CP13 is that idea in one flask: a named non-pathogen, aseptic samples, a growth…Specification 6.4Read & use the scienceClose article
Why this matters
The Microbiology Society’s case for laboratory microbiology still assumes you know what you inoculated. CP13 is that idea in one flask: a named non-pathogen, aseptic samples, a growth measure, and a kill step. CDC and NIH disease pages on this course are for TB and HIV mechanisms, not for choosing a school culture. The professional parallel is quality control: a culture scientist records the inoculum, medium, temperature and sampling times before estimating growth. Turbidity is quick, but it counts how much light the suspension blocks, not automatically how many live cells remain. The school practical should never use an unknown environmental isolate to make the story more dramatic. Safety and validity both depend on knowing the material.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 6.4 Core Practical 13: investigate microorganism growth rate in a liquid culture, including safe and ethical use.
Use the science
Why would “we swabbed the canteen floor so it would be more real” fail this practical?
Explore a possible response
Unknown mixed environmental samples can include pathogens, cannot be named, and are not an ethical or valid school culture for a growth-rate investigation.
Explore the source
- Microbiology Society: what is microbiologyMicrobiology Society
A cloudy flask is not a census of living cells
CP13 · Growth of Microorganisms in Liquid CultureResearchers use optical density, or OD, to follow microbial cultures quickly because a denser suspension blocks or scatters more light. A published calibration study compared OD readings with…Specification 6.4Read & use the scienceClose article
Why this matters
Researchers use optical density, or OD, to follow microbial cultures quickly because a denser suspension blocks or scatters more light. A published calibration study compared OD readings with viable cell counts and corrected readings against a blank. That matters for Core Practical 13: turbidity is an indirect measure of growth, and one OD value does not automatically equal a particular number of live microorganisms. Cells differ in size and cultures can contain dead material. A blank, dilution and a calibration relationship help turn a convenient signal into an interpretable measurement.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 6.4 Core Practical 13: investigate microorganism growth rate in a liquid culture, including safe and ethical use.
Use the science
Why could two cultures have the same optical density but different viable cell counts?
Explore a possible response
Light scattering depends on more than live cell number: cell size, debris and dead cells can contribute. A viable count or calibration is needed before equating OD with living cells.
Explore the source
- Estimating microbial population data from optical densityPeer-reviewed study (PMC)
The same lawn logic as professional disc tests, without the brand codes
CP14 · The Effect of Antibiotics on BacteriaClinical disc-diffusion methods compare zones only under specified conditions. EUCAST publishes the standardised method and interpretive criteria used in that setting. Your school plate uses a similar bacterial…Specification 6.14Read & use the scienceClose article
Why this matters
Clinical disc-diffusion methods compare zones only under specified conditions. EUCAST publishes the standardised method and interpretive criteria used in that setting. Your school plate uses a similar bacterial lawn and measured inhibition zone, but its discs and organism need not match a clinical test. Report the millimetres and the limits, not a patient-level sensitive or resistant label. In a clinical laboratory, disc diffusion is standardised because agar depth, inoculum density, disc content and incubation can all alter the zone. EUCAST provides method and interpretation rules for that setting. A school plate teaches the measurement and the need for controls; it cannot diagnose a patient or justify an antibiotic choice. A zone diameter without the organism and standard method is not a clinical category.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 6.14 Core Practical 14: investigate the effects of different antibiotics on bacteria.
Use the science
Why would copying a commercial kit’s “sensitive/resistant” key into your book as “our result” fail the practical?
Explore a possible response
Those cut-offs belong to a standardised medical test. Your plate, organism and discs may differ. You should report measured zones and a cautious interpretation, not an imported diagnosis.
Explore the source
Go to the lesson: The Effect of Antibiotics on Bacteria →A hospital resistance map starts with comparable tests
CP14 · The Effect of Antibiotics on BacteriaThe World Health Organization’s GLASS system collects antimicrobial-resistance information using standardised surveillance methods. A school disc-diffusion plate is a useful first step in understanding why a bacterial lawn…Specification 6.14Read & use the scienceClose article
Why this matters
The World Health Organization’s GLASS system collects antimicrobial-resistance information using standardised surveillance methods. A school disc-diffusion plate is a useful first step in understanding why a bacterial lawn and measured zone matter, but it is not a national surveillance record. Different organisms, antibiotics and laboratory methods can produce different zone sizes. To compare places or years, researchers need consistent definitions and quality checks. A small school zone is evidence about that plate under those conditions; it cannot by itself show that resistance is rising in a country.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32 · assessed through Unit 6. The application extends beyond required recall.
- 6.14 Core Practical 14: investigate the effects of different antibiotics on bacteria.
Use the science
Why can a single small inhibition zone not establish a national trend in antibiotic resistance?
Explore a possible response
It is one result for one organism, disc and method. A trend needs comparable tests across many clinical isolates and time points, with standard interpretation and sampling.
Explore the source
- Global Antimicrobial Resistance and Use Surveillance SystemWorld Health Organization
Yeast is chosen because it is a manageable living cell
CP15 · Respiration in YeastThe Microbiology Society introduces microorganisms as organisms that can be studied. That is the limit of the citation. It does not specify methylene blue times or a safe…Specification 7.7Read & use the scienceClose article
Why this matters
The Microbiology Society introduces microorganisms as organisms that can be studied. That is the limit of the citation. It does not specify methylene blue times or a safe concentration. Your method is a school assay of hydrogen transfer, not an identification key. Dough rising is a familiar food image, but it follows carbon dioxide, not the redox change the specified investigation uses. The indicator accepts hydrogen as yeast metabolises substrate; decolourisation time can be compared only when starting colour, yeast amount and temperature are held constant. A shorter time suggests faster dye reduction under those conditions. It is not a direct measurement of ATP yield or a complete map of aerobic and anaerobic pathways.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.7 Core Practical 15: use an artificial hydrogen carrier (redox indicator) to investigate respiration in yeast.
Use the science
Why is a photograph of bread dough not a result for this practical?
Explore a possible response
Rising dough may show carbon dioxide production. Core Practical 15 asks for the indicator colour change as a hydrogen-carrier measurement. A different observation needs a different conclusion.
Explore the source
- Microbiology Society: what is microbiologyMicrobiology Society
A blue dye can report a changing yeast state
CP15 · Respiration in YeastResearchers have used methylene blue staining while following the viability of yeast grown under different metabolic conditions. Core Practical 15 asks a more specific question: an artificial hydrogen…Specification 7.7Read & use the scienceClose article
Why this matters
Researchers have used methylene blue staining while following the viability of yeast grown under different metabolic conditions. Core Practical 15 asks a more specific question: an artificial hydrogen carrier changes colour as it is reduced during yeast respiration. The shared lesson is that a colour is a proxy for cell activity, not a direct picture of ATP molecules. Dye concentration, oxygen exposure and the amount of yeast affect the time to a visible change. A kitchen fermentation story may be memorable, but its dough volume is a different observable.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.7 Core Practical 15: use an artificial hydrogen carrier (redox indicator) to investigate respiration in yeast.
Use the science
Why would a faster loss of dye colour not prove that each yeast cell produced more ATP?
Explore a possible response
The result is the rate of indicator reduction for the whole sample. Different cell numbers, dye concentration or oxygen conditions could change the time without showing ATP yield per cell.
Explore the source
- Metabolic remodelling during yeast cultivationPeer-reviewed study (PMC)
Lungs are not a seed chamber
CP16 · Rate of Respiration and Respiratory QuotientNHLBI describes human lungs moving oxygen into blood and carbon dioxide out. A seed respirometer is a different measurement: volume change in a closed tube around the material.…Specification 7.8Read & use the scienceClose article
Why this matters
NHLBI describes human lungs moving oxygen into blood and carbon dioxide out. A seed respirometer is a different measurement: volume change in a closed tube around the material. Use the lung page only to keep breathing distinct from this practical. It is not a method sheet. A sealed seed chamber makes oxygen uptake visible as a tiny displacement. Carbon dioxide absorption changes which gas contributes to that displacement, and leaks or temperature changes can mimic respiration. The control tube therefore matters before any rate is calculated. A mammal's lungs exchange gases with blood, whereas a seed has no lungs; borrowing a breathing-rate figure from a human source would confuse ventilation with cellular respiration.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.8 Core Practical 16: use a simple respirometer to determine respiration rate and respiratory quotient of suitable material.
Use the science
Why would quoting a human breathing rate not answer a seed respirometer question?
Explore a possible response
The material, the closed tube and the carbon dioxide absorbent are different. Rate must come from the volume change you corrected and calibrated.
Explore the source
- NHLBI: how the lungs workNHLBI, NIH
Seed oxygen use can test seed quality
CP16 · Rate of Respiration and Respiratory QuotientA seed-metabolism study measured oxygen consumption in small respirometry chambers across many angiosperm species. Researchers are interested in whether metabolism relates to germination, ecology and storage. This is…Specification 7.8Read & use the scienceClose article
Why this matters
A seed-metabolism study measured oxygen consumption in small respirometry chambers across many angiosperm species. Researchers are interested in whether metabolism relates to germination, ecology and storage. This is recognisably connected to Core Practical 16, although a research instrument is more sensitive than a school capillary tube. Oxygen uptake can change with seed size, water uptake and temperature, so comparisons need rates per mass or per seed under stated conditions. Oxygen uptake alone gives a respiration rate; respiratory quotient additionally needs carbon dioxide production.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.8 Core Practical 16: use a simple respirometer to determine respiration rate and respiratory quotient of suitable material.
Use the science
Why is “one large seed moved the marker farther” insufficient evidence that its cells respire faster than those of a small seed?
Explore a possible response
The large seed may contain more respiring tissue. Compare oxygen uptake per unit mass and time under the same conditions, and include a control for non-biological gas movement.
Explore the source
- Metabolic rate of angiosperm seedsPeer-reviewed study (PMC)
Spirometer and spirometry are not automatic synonyms
CP17 · Exercise and Respiratory MeasurementsThe NHS uses spirometry for a clinic test of how much air a person can blow out. Your practical uses spirometer traces for ordinary breaths and oxygen use.…Specification 7.15Read & use the scienceClose article
Why this matters
The NHS uses spirometry for a clinic test of how much air a person can blow out. Your practical uses spirometer traces for ordinary breaths and oxygen use. The shared root is the enrichment warning: read which volumes the question named before you calculate. A clinician may use forced expiration to investigate obstruction, while an exercise physiologist asks how ordinary ventilation and oxygen consumption change as workload rises. Both use respiratory measurements but answer different questions. On a trace, tidal volume is the vertical difference for one ordinary breath and minute ventilation also needs the number of breaths per minute. A large forced breath is not the representative breath for that calculation.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.15 Core Practical 17: use spirometer traces to investigate exercise effects on tidal volume, breathing rate, minute ventilation and oxygen consumption.
Use the science
A question asks for tidal volume. Why is a forced one-second blow the wrong measurement to copy from a clinic leaflet?
Explore a possible response
That blow is a lung-function test, not one resting or exercising breath. Tidal volume is the ordinary breath on the trace you were given.
Explore the source
Go to the lesson: Exercise and Respiratory Measurements →The exercise mask asks a broader question
CP17 · Exercise and Respiratory MeasurementsNHLBI describes cardiopulmonary exercise testing as combining exercise workload with ECG, blood pressure and analysis of exhaled gases. An exercise physiologist can ask whether a limitation is mainly…Specification 7.15Read & use the scienceClose article
Why this matters
NHLBI describes cardiopulmonary exercise testing as combining exercise workload with ECG, blood pressure and analysis of exhaled gases. An exercise physiologist can ask whether a limitation is mainly cardiac, pulmonary or related to effort. Core Practical 17 uses a spirometer trace to calculate tidal volume, breathing rate, minute ventilation and oxygen consumption. Those trace quantities are part of the larger physiological story, but a school graph cannot diagnose a disease. An increase in breathing rate alone also does not tell you how much air moves per breath.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 7.15 Core Practical 17: use spirometer traces to investigate exercise effects on tidal volume, breathing rate, minute ventilation and oxygen consumption.
Use the science
Two people have the same breathing rate after exercise. Why might their minute ventilations differ?
Explore a possible response
Minute ventilation is breathing rate multiplied by tidal volume. Equal rates can accompany different volumes per breath, so both must be measured from the trace.
Explore the source
Go to the lesson: Exercise and Respiratory Measurements →Compost microbes are a different starch story
CP18 · Amylase Production in Germinating Cereal GrainsThe US EPA says microorganisms break down organic material in compost. They use extracellular enzymes too. Core Practical 18 is not that community. The enzyme comes from the…Specification 8.12Read & use the scienceClose article
Why this matters
The US EPA says microorganisms break down organic material in compost. They use extracellular enzymes too. Core Practical 18 is not that community. The enzyme comes from the grain’s aleurone after a gibberellin signal. A clear zone next to a half-grain is not evidence that compost bacteria were on the plate, especially if the no-grain plate stays blue-black. Compost is a useful contrast because its mixed microorganisms release enzymes outside their cells to dismantle organic matter. In a germinating cereal grain, gibberellin signalling triggers amylase production by the grain itself. Both can clear starch, but the mechanism and organism differ. A no-grain control and an ungerminated comparison help you decide whether clearing is associated with the grain treatment rather than contamination or a property of the agar.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 8.12 Core Practical 18: investigate amylase production in germinating cereal grains.
Use the science
Why would swabbing a compost heap onto the same agar answer a different question?
Explore a possible response
That would test microbial enzymes from the heap. This practical tests whether the grain produces amylase when the embryo or gibberellin is present. The organisms are not the same.
Explore the source
- US EPA: composting at homeUS Environmental Protection Agency
Malting connects a cereal grain to gene expression
CP18 · Amylase Production in Germinating Cereal GrainsA study of germinating barley measured gibberellin-related transcripts and enzyme activity in different grain tissues. It links Core Practical 18 to cereal science: amylase production helps mobilise stored…Specification 8.12Read & use the scienceClose article
Why this matters
A study of germinating barley measured gibberellin-related transcripts and enzyme activity in different grain tissues. It links Core Practical 18 to cereal science: amylase production helps mobilise stored starch as a seedling begins to grow, and the same chemistry matters during malting. A starch-clearing zone is a useful school proxy for secreted enzyme action, not a direct measurement of every gene transcript. The researcher can compare treated and untreated grain, but must also control germination time and tissue position before attributing a difference to gibberellin.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38 · assessed through Unit 6. The application extends beyond required recall.
- 8.12 Core Practical 18: investigate amylase production in germinating cereal grains.
Use the science
Why might two barley halves show different starch-clearing zones even if they received the same gibberellin treatment?
Explore a possible response
They may differ in germination stage, tissue position, starting starch or enzyme amount. A controlled comparison needs matched material and equal incubation conditions.
Explore the source
- Gibberellin expression and content in germinated barleyPeer-reviewed study (PMC)
Failing to reject is not proof
P1 · A null hypothesis and the variablesThe NIST engineering statistics handbook describes a statistical test as a way to decide whether there is enough evidence to reject a null hypothesis. Not rejecting it can…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
The NIST engineering statistics handbook describes a statistical test as a way to decide whether there is enough evidence to reject a null hypothesis. Not rejecting it can mean the null is reasonable, or that the study did not collect enough evidence. That handbook is enrichment. It is not a Unit 6 mark scheme, and it does not supply a critical value for your question. The word ‘null’ can sound like a prediction that nothing will happen. It is instead the starting comparison that a test may challenge. A clinical or ecological study has to define the outcome and comparison groups before inspecting results. If investigators change the endpoint after seeing the data, the apparent evidence is harder to interpret. At A level, write the null in terms of the variables actually measured, not the result you hope for.
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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
A plan says that if the means are similar the null hypothesis has been proved. Why is that too strong?
Explore a possible response
Similar means may simply fail to provide enough evidence to reject the null. Failure to reject is not proof that the null is true, and a plan cannot know that outcome before the data exist.
Explore the source
Go to the lesson: A null hypothesis and the variables →A trial names its endpoint before it begins
P1 · A null hypothesis and the variablesAn NIH clinical-trials glossary defines an endpoint as the outcome selected for analysis of a treatment’s safety or benefit. That is a real-world version of the Unit 6…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
An NIH clinical-trials glossary defines an endpoint as the outcome selected for analysis of a treatment’s safety or benefit. That is a real-world version of the Unit 6 planning demand to identify the dependent variable and state a testable hypothesis. If a trial changes from a measured symptom score to a different outcome after seeing its results, its conclusion is harder to assess. School investigations are much smaller, but they should also name the groups, the measurement and the time point before collecting data. The null compares those named quantities.
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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
A plan says only “the treatment helps plants”. What would you add to make a null hypothesis testable?
Explore a possible response
Name the treatment and comparison groups, a measurable outcome such as mean shoot length, and a time point; then state that the mean outcome does not differ between groups.
Explore the source
- Endpoint: clinical trial glossaryNCATS, NIH
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.
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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
Go to the lesson: Apparatus, calibration and the data you will use →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.
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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.
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Go to the lesson: Apparatus, calibration and the data you will use →Replace, reduce, refine — when animals are actually the subject
P3 · Repeats, risk and living organismsThe NC3Rs describes three principles for more humane animal research: replacement with methods that do not use animals, reduction by using well-designed studies, and refinement by reducing pain,…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
The NC3Rs describes three principles for more humane animal research: replacement with methods that do not use animals, reduction by using well-designed studies, and refinement by reducing pain, suffering and distress. School practicals are not research laboratories. The principles are enrichment, not a Pearson mark scheme and not a ban you should quote in place of the question. The 3Rs are used when animal research is genuinely proposed. They do not mean that every school seed or yeast investigation needs the same argument. For any living subject, ask what harm the method might cause and whether a less harmful method could answer the question. If human volunteers are involved, their choice and privacy are separate ethical concerns. The response must match the organism in the question.
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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
A plan uses fifty animals where a pilot could have shown that five, properly controlled, would answer the question. Which of the three ideas does that problem illustrate?
Explore a possible response
Reduction: the number of animals is higher than the design needs. It is not, by itself, a reason to skip a hazard control or to change the variables.
Explore the source
- NC3Rs: the 3RsNC3Rs
A volunteer is more than a data point
P3 · Repeats, risk and living organismsUS human-research guidance treats informed consent as an ongoing process: a participant receives relevant information, understands it and chooses voluntarily. A school exercise practical is not automatically a…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
US human-research guidance treats informed consent as an ongoing process: a participant receives relevant information, understands it and chooses voluntarily. A school exercise practical is not automatically a regulated clinical study, but it still involves a person who should be able to decline, stop and avoid sharing identifying health details. This extends Unit 6’s instruction to identify ethical issues with living organisms. It is separate from the physical safety of exercise equipment. A safe protocol can still be unethical if participation is pressured or private measurements are displayed publicly.
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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 are a clear stop rule and voluntary participation two different safeguards in a breathing investigation?
Explore a possible response
A stop rule reduces physical risk if someone becomes unwell; voluntary participation respects the person’s choice to take part at all. Both matter, and neither replaces the other.
Explore the source
- Informed consent FAQsU.S. Department of Health and Human Services
Extra digits are not extra information
I1 · Readings, range and significant figuresNIST’s guide to the SI includes rules for expressing the value of a quantity, units included. A school table is not that publication. The transferable rule is smaller:…Specification Unit 6 · Implementation and measurementsRead & use the scienceClose article
Why this matters
NIST’s guide to the SI includes rules for expressing the value of a quantity, units included. A school table is not that publication. The transferable rule is smaller: do not print digits the measuring instrument did not justify. A long calculator display is a calculation, not a new observation. A laboratory scientist records the instrument's resolution, repeats and variation so a reader can judge what digits are defensible. Rounding a mean too early can discard information, but printing ten decimal places after reading a ruler to millimetres pretends certainty. Show the working with adequate digits, then report a result at a precision supported by the measurements.
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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
A mean of whole-second times is printed as 41.6667 s. What information do the extra digits seem to add, and why is that misleading?
Explore a possible response
They look like a measurement to ten-thousandths of a second. The clocks were read to the nearest second, so those digits are an artefact of the division, not a finer observation.
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Go to the lesson: Readings, range and significant figures →A quantity without a unit is unfinished
I2 · Wrong units and a point that does not fitNational measurement laboratories publish the SI so that a result can be compared in a stated unit. School data are not a standards-laboratory report. Two numbers can still…Specification Unit 6 · Implementation and measurementsRead & use the scienceClose article
Why this matters
National measurement laboratories publish the SI so that a result can be compared in a stated unit. School data are not a standards-laboratory report. Two numbers can still not be compared until the unit is the one that was measured. A number can be copied perfectly and still be unusable if its unit is wrong. Unit conversion is a scientific operation, not a cosmetic label change. Before plotting or comparing two studies, check whether mass is in grams or kilograms and whether a rate means per second or per minute. A tenfold or thousandfold mistake can overwhelm a real biological effect while leaving a neat-looking graph.
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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
Two students both record 12.5 for a leaf. Why might those records still disagree?
Explore a possible response
The unit may differ. 12.5 cm and 12.5 m are not the same length. The heading has to name the unit that matches the ruler, or the numbers have to be converted.
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Go to the lesson: Wrong units and a point that does not fit →The Mars probe lost in a unit conversion
I2 · Wrong units and a point that does not fitNASA Jet Propulsion Laboratory describes the loss of the Mars Climate Orbiter after a failure to translate English units into metric units in navigation data. Spacecraft engineering is…Specification Unit 6 · Implementation and measurementsRead & use the scienceClose article
Why this matters
NASA Jet Propulsion Laboratory describes the loss of the Mars Climate Orbiter after a failure to translate English units into metric units in navigation data. Spacecraft engineering is far beyond a Biology practical, but the lesson is exactly why Unit 6 asks you to amend incorrect units. A value without a unit cannot be checked, and a mislabeled rate may change a result by a factor of 60 or 1000. Put the unit in the table heading, convert explicitly and then use the converted value throughout the calculation and graph.
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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
A gas rate is recorded as 12 cm³ min⁻¹ but labelled 12 cm³ s⁻¹. By what factor is the labelled rate wrong?
Explore a possible response
One minute contains 60 seconds. The true rate is 12/60 = 0.20 cm³ s⁻¹, so the wrongly labelled 12 cm³ s⁻¹ is 60 times too high.
Explore the source
- Mars Climate Orbiter missionNASA Jet Propulsion Laboratory
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.
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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.
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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)
The unit is part of the result
A1 · Tables, units and processed numbersThe organisations that maintain the SI treat the unit as part of how a quantity is stated. In a school table the same rule is practical: a heading…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
The organisations that maintain the SI treat the unit as part of how a quantity is stated. In a school table the same rule is practical: a heading without a unit, or a processed number that has lost its unit, is unfinished even when the arithmetic is right. In a shared research dataset, a column heading is part of the measurement record. Without a unit or definition, another laboratory cannot distinguish raw observations from calculated rates. Keeping repeats visible lets a reader see scatter rather than only a polished mean. The same habit helps in Unit 6: put units in headings, separate raw and processed values and use enough significant figures to make the calculation checkable.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
A mean is calculated correctly as 2.0 but the column has no unit. Is the processing finished?
Explore a possible response
No. 2.0 g and 2.0 kg are different results. The unit has to stay with the processed number, usually in the heading.
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Go to the lesson: Tables, units and processed numbers →A reusable table needs a readable method
A1 · Tables, units and processed numbersThe FAIR principles aim to make research data findable, accessible under appropriate conditions, interoperable and reusable. A biology table can be numerically correct yet difficult to reuse if…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
The FAIR principles aim to make research data findable, accessible under appropriate conditions, interoperable and reusable. A biology table can be numerically correct yet difficult to reuse if it lacks units, definitions, replicate identifiers or the method used to calculate rates. This extends Unit 6 analysis: separate raw readings from processed results so a reader can reconstruct the calculation. FAIR does not mean posting participant data publicly; access can be restricted where privacy requires it. The practical lesson is that a table should travel with enough context to remain meaningful.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
Why is a column headed only “rate = 3.2” unsuitable for a shared respiration dataset?
Explore a possible response
It lacks the quantity definition and units, such as cm³ O₂ g⁻¹ min⁻¹, plus the method and replicate. Another reader cannot compare or reproduce the value reliably.
Explore the source
- FAIR guiding principles for scientific data managementPeer-reviewed research (PMC)
A log scale is a last resort for clarity, and it must be obvious
A2 · Scales, log axes and gradientsOffice for National Statistics guidance says linear scales are easier to read than log scales, and that log scales should be avoided unless the data cannot be shown…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
Office for National Statistics guidance says linear scales are easier to read than log scales, and that log scales should be avoided unless the data cannot be shown clearly another way. Official charts are not examination answers. The warning still helps: a log axis changes what a slope means, so it has to be labelled and chosen for a reason. A logarithmic axis can compress a range that spans several orders of magnitude. That can reveal a multiplicative pattern, but it can also make a rapid increase look less dramatic to a casual reader. State the axis scale and units before describing a gradient. For a straight line on a log-y graph, equal vertical steps mean equal ratios rather than equal additions; it is not an ordinary linear increase.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
Why can a log scale make a multiplying population look like a steady straight line?
Explore a possible response
Equal steps on a log axis are equal multiplications. A population that doubles at a constant interval becomes evenly spaced on a log scale, so the line looks straight even though the raw counts are accelerating.
Explore the source
- Office for National Statistics: chart axes and gridlinesOffice for National Statistics
A growth curve can hide its scale
A2 · Scales, log axes and gradientsResearchers studying bacterial growth often plot optical density against time and use logarithmic transformations when populations span a wide range. A study of high-throughput growth measurements discusses lag…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
Researchers studying bacterial growth often plot optical density against time and use logarithmic transformations when populations span a wide range. A study of high-throughput growth measurements discusses lag time and maximum growth rate in culture. Core Practical 13 gives this biological context, while Unit 6 analysis asks you to choose an appropriate graph scale and interpret its gradient. A straight segment on a log-transformed y-axis indicates approximately constant proportional growth, not a fixed number of new cells each minute. Axis labels must disclose the transformation.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
If an OD series doubles at equal time intervals, why might log(OD) against time look straight while raw OD against time curves upward?
Explore a possible response
Equal multiplications become equal additions after taking logs. Raw OD gains larger absolute amounts each interval, so the untransformed graph bends upward.
Explore the source
- Environmental factors in high-throughput bacterial growth measurementsPeer-reviewed study (PMC)
A test statistic is not a decision until it is compared
A3 · Patterns, tests and realistic changesThe NIST engineering statistics handbook describes rejecting a null hypothesis when the test statistic falls in a rejection region set by a critical value, or when a p-value…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
The NIST engineering statistics handbook describes rejecting a null hypothesis when the test statistic falls in a rejection region set by a critical value, or when a p-value is compared with a level chosen in advance. The choice of that level is a convention, not a result hiding inside your graph. School questions that want a decision give you the critical value. The test statistic is a summary calculated from a particular data set under assumptions about that test. It is not a verdict printed inside the raw number. A decision depends on the correct test, degrees of freedom and threshold or critical value supplied for the comparison. Even a statistically significant difference does not by itself show a large or medically important effect. Start with the pattern, then state exactly what the data allow.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
A calculated chi-squared value is 6.67 and the question prints no critical value. Why is “the result is significant” not yet justified?
Explore a possible response
Significance here means the statistic has been compared with a critical value, or a stated p-value threshold. 6.67 by itself is only the result of the sum. It does not contain the comparison.
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Go to the lesson: Patterns, tests and realistic changes →A small p-value is not a large biological effect
A3 · Patterns, tests and realistic changesThe American Statistical Association cautions that a p-value does not measure the size or importance of an effect. It also does not give the probability that the null…Specification Unit 6 · AnalysisRead & use the scienceClose article
Why this matters
The American Statistical Association cautions that a p-value does not measure the size or importance of an effect. It also does not give the probability that the null hypothesis is true. In Unit 6, a test statistic and supplied critical value may justify calling a result significant, but the biological pattern still needs description. A tiny difference measured very precisely may be statistically detectable yet unimportant for an organism. Conversely, a small study can miss a meaningful effect. The graph, design and uncertainty belong beside the formal decision.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Analysis Tabulate, calculate, graph and interpret data, including possible logarithmic scales, gradients, uncertainty and realistic modifications.
Use the science
Two treatments differ by only 0.1 mm in mean growth, with a statistically significant result. What else should be reported?
Explore a possible response
Report the effect size, variation or uncertainty, sample design and biological context. Statistical significance alone does not show that 0.1 mm matters in practice.
Explore the source
- ASA statement on statistical significance and p-valuesAmerican Statistical Association