Unit 5 biology.
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From mitochondria and exercise to brain imaging, plant signals and genetic medicines. Follow Unit 5 science into real work, research and claims worth testing.
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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.
78 articles across Unit 5. An article can belong to more than one theme.
The large yield needed a mechanism, not a bigger explosion
7A · Respiration in CellsThe 1978 Nobel Prize in Chemistry recognised Peter Mitchell for the chemiosmotic theory of biological energy transfer. That theory is the membrane-gradient explanation you meet in 7A 4.…Specification 7.1(i)Read & use the scienceClose article
Why this matters
The 1978 Nobel Prize in Chemistry recognised Peter Mitchell for the chemiosmotic theory of biological energy transfer. That theory is the membrane-gradient explanation you meet in 7A 4. It is enrichment here: 7.1 only asks you to know that a large amount of energy is transferred, and that the chemistry is stepped. 7.1: carbon dioxide is released and hydrogen meets oxygen, with a large energy transfer spread across many enzyme-controlled steps.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.1(i) Overall aerobic respiration: substrate, carbon dioxide, oxygen and energy transfer.
Use the science
Why is “Mitchell discovered a new enzyme that burns glucose” a poor summary of why this prize is linked to 7.1?
Explore a possible response
The prize was for a theory of how energy is transferred across membranes, not for naming a glucose-burning enzyme. Enzyme names are not the 7.1 requirement anyway.
Explore the source
- Nobel Prize in Chemistry 1978: chemiosmotic theoryNobel Prize Outreach
When mitochondria cannot meet demand
7A · Respiration in CellsThe US neurological institute describes mitochondrial disorders that can affect muscles, nerves, the heart and several other organs. Those tissues have high energy demands, so disruption of mitochondrial…Specification 7.1(i)Read & use the scienceClose article
Why this matters
The US neurological institute describes mitochondrial disorders that can affect muscles, nerves, the heart and several other organs. Those tissues have high energy demands, so disruption of mitochondrial function may have effects in more than one body system. The connection to 7.1 is the scale of energy transfer made available by aerobic respiration, not a claim that every disorder blocks the same step. A diagnosis needs evidence about the particular defect; the word “mitochondrial” alone does not identify an enzyme or predict one symptom. This is why a biological mechanism and a clinical label are different levels of explanation.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.1(i) Overall aerobic respiration: substrate, carbon dioxide, oxygen and energy transfer.
Use the science
Why might a mitochondrial defect affect both a skeletal muscle and a neurone, yet cause different symptoms?
Explore a possible response
Both tissues depend on ATP from respiration, but they use it for different tasks: contraction in muscle and ion gradients or signalling in neurones. The affected pathway and distribution of defective mitochondria also matter.
Explore the source
- Mitochondrial disordersUS National Institute of Neurological Disorders and Stroke
A lactate number is a blood test
7A · Glycolysis and Anaerobic RespirationMedlinePlus describes a lactate test as a clinical measurement. Lactate can rise during hard exercise, when oxygen demand is high, and also in illness. The page is about…Specification 7.2Read & use the scienceClose article
Why this matters
MedlinePlus describes a lactate test as a clinical measurement. Lactate can rise during hard exercise, when oxygen demand is high, and also in illness. The page is about detecting a high level. It is not a description of the liver converting lactate back to pyruvate, and it does not say that lactate causes muscle soreness. 7.2 and 7.5: lactate is the anaerobic product in animals, then a substrate the liver can turn back into pyruvate.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.2 Glycolysis in aerobic and anaerobic respiration.
Use the science
Why is “my lactate test was high, so my liver enzymes have the wrong names” a muddle of this lesson?
Explore a possible response
A high reading means a lot of lactate was in the sample at that time. It does not name glycolytic enzymes, which are not required anyway. The fate of lactate is still blood to liver to pyruvate.
Explore the source
- MedlinePlus: lactate testUS National Library of Medicine
Cancer cells rewrite the glycolysis story
7A · Glycolysis and Anaerobic RespirationMany proliferating cancer cells take up much glucose and make lactate even when oxygen is available. Researchers call this aerobic glycolysis or the Warburg effect. The NCI account…Specification 7.2Read & use the scienceClose article
Why this matters
Many proliferating cancer cells take up much glucose and make lactate even when oxygen is available. Researchers call this aerobic glycolysis or the Warburg effect. The NCI account makes clear that the reason remains an active research question; it should not be reduced to “cancer cells have broken mitochondria”. Your 7.2 route still applies: glycolysis makes pyruvate, reduced coenzyme and a little ATP. The extension is that cells can route carbon and regenerate oxidised coenzyme in different ways while building new material. A high lactate reading is therefore not, by itself, proof that oxygen was absent.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.2 Glycolysis in aerobic and anaerobic respiration.
Use the science
Why does lactate production by an oxygenated tumour cell not prove that all its mitochondria have stopped working?
Explore a possible response
Lactate can regenerate oxidised NAD after glycolysis even while oxygen is present. The cell may still use mitochondrial reactions; lactate alone does not measure those reactions.
Explore the source
- New clarity on the Warburg effectUS National Cancer Institute
The carbon dioxide in your breath was chemistry first
7A · The Krebs CycleNHLBI describes the lungs as the place where oxygen enters the blood and carbon dioxide leaves it. That is ventilation and gas exchange. The carbon dioxide itself was…Specification 7.3Read & use the scienceClose article
Why this matters
NHLBI describes the lungs as the place where oxygen enters the blood and carbon dioxide leaves it. That is ventilation and gas exchange. The carbon dioxide itself was produced by decarboxylation in cells. The lung page does not teach the Krebs cycle, and it does not treat breathing as cellular respiration. 7.3: carbon dioxide is formed by decarboxylation in the link reaction and the Krebs cycle, in mitochondria. A measured gas or ATP change cannot, on its own, identify every intermediate enzyme or show which step changed.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.3 Link reaction and Krebs cycle: carbon dioxide, ATP and reduced coenzymes.
Use the science
Why is “I breathed out, so my lungs ran the Krebs cycle” incorrect?
Explore a possible response
Breathing exhales carbon dioxide that cells have already produced. The cycle runs in mitochondrial matrices, not in the lung airway.
Explore the source
- NHLBI: how the lungs workUS National Heart, Lung, and Blood Institute
Carbon can leave before the chain begins
7A · The Krebs CycleThe NCI discussion of tumour metabolism follows carbon from glucose into pathways used for growth. It notes that changing the fate of pyruvate can change how much carbon…Specification 7.3Read & use the scienceClose article
Why this matters
The NCI discussion of tumour metabolism follows carbon from glucose into pathways used for growth. It notes that changing the fate of pyruvate can change how much carbon enters mitochondrial metabolism. This gives a real reason to keep 7.3 distinct from 7.4: the link reaction and Krebs cycle release carbon dioxide and supply reduced coenzymes, while the electron transport chain handles their electrons later. A change in carbon dioxide output might reflect substrate choice or pathway use; it does not locate a mutation by itself. The cancer setting is an application of carbon flow, not an extra Krebs intermediate to memorise.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.3 Link reaction and Krebs cycle: carbon dioxide, ATP and reduced coenzymes.
Use the science
If less pyruvate enters the link reaction, what happens to its direct carbon dioxide output and to the supply of reduced coenzymes?
Explore a possible response
Both would tend to fall from that route: less pyruvate is decarboxylated, and less substrate reaches the reactions that reduce NAD and FAD. Other fuels could complicate a whole-cell measurement.
Explore the source
- New clarity on the Warburg effectUS National Cancer Institute
The gradient was the disputed idea
7A · The Electron Transport ChainPeter Mitchell received the 1978 Nobel Prize in Chemistry for the chemiosmotic theory. The award summary describes it as a contribution to understanding biological energy transfer. It covers…Specification 7.4Read & use the scienceClose article
Why this matters
Peter Mitchell received the 1978 Nobel Prize in Chemistry for the chemiosmotic theory. The award summary describes it as a contribution to understanding biological energy transfer. It covers the idea you use here for mitochondria, and the same kind of gradient is used in chloroplasts. The page is not a list of carrier proteins. 7.4: oxidative phosphorylation depends on a proton gradient and ATP synthase, fed by the electron transport chain.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.4 Oxidative phosphorylation, electron transport, chemiosmosis and ATP synthase.
Use the science
Why is the prize relevant to mitochondria and still not a reason to memorise cytochrome names?
Explore a possible response
The theory is about the proton gradient driving ATP synthesis. Carrier names are not in specification 7.4.
Explore the source
- Nobel Prize in Chemistry 1978: chemiosmotic theoryNobel Prize Outreach
Brown fat spends a gradient on heat
7A · The Electron Transport ChainBrown adipose tissue contains mitochondria with UCP1, a protein that can let protons cross the inner membrane without driving ATP synthase. Energy from the gradient is then released…Specification 7.4Read & use the scienceClose article
Why this matters
Brown adipose tissue contains mitochondria with UCP1, a protein that can let protons cross the inner membrane without driving ATP synthase. Energy from the gradient is then released mainly as heat. This is a deliberate physiological use of uncoupling, not a statement that ATP synthase is unnecessary in ordinary respiration. Your 7.4 model helps predict the trade-off: electron transport may continue to build a gradient, but a proton leak leaves less gradient available for oxidative phosphorylation. Researchers study how cold exposure regulates this tissue. A school diagram of one mitochondrion cannot tell you the whole-body rate of heat production.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.4 Oxidative phosphorylation, electron transport, chemiosmosis and ATP synthase.
Use the science
If proton leakage through UCP1 increased while electron supply stayed similar, why might oxygen use continue while ATP yield falls?
Explore a possible response
Electron transport can still transfer electrons to oxygen, but some proton flow returns through UCP1 rather than ATP synthase. Less of the gradient drives ATP synthesis and more energy becomes heat.
Explore the source
- Brown fat as a regulator of metabolismScientific review via NIH PubMed Central
Yeast is a cell with a metabolism, not an RQ chart
7A · Respiratory Substrates and Respiratory QuotientThe Microbiology Society’s introduction treats microorganisms as living things you can investigate. It does not publish a table of respiratory quotients. Yeast can be the material in a…Specification 7.6Read & use the scienceClose article
Why this matters
The Microbiology Society’s introduction treats microorganisms as living things you can investigate. It does not publish a table of respiratory quotients. Yeast can be the material in a respirometer or a dye tube. Any RQ still has to be calculated from the two gases you measured. 7.6: RQ is CO₂ produced divided by O₂ consumed. The organism only supplies the gases. A measured gas or ATP change cannot, on its own, identify every intermediate enzyme or show which step changed.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.6 Respiratory quotient and the gases used to calculate it.
Use the science
Why does “it is yeast, so the RQ is 1” fail?
Explore a possible response
The substrate and whether oxygen is available change the gases. Yeast on glucose in air can be near 1. The same yeast fermenting, or a seed using lipid, will not match that assumption. You calculate the ratio from data.
Explore the source
- Microbiology Society: what is microbiologyMicrobiology Society
A fuel leaves a signature in two gases
7A · Respiratory Substrates and Respiratory QuotientIndirect calorimetry compares oxygen consumed with carbon dioxide produced to investigate fuel use. The respiratory quotient is the carbon dioxide volume divided by the oxygen volume, so a…Specification 7.6Read & use the scienceClose article
Why this matters
Indirect calorimetry compares oxygen consumed with carbon dioxide produced to investigate fuel use. The respiratory quotient is the carbon dioxide volume divided by the oxygen volume, so a single gas reading is not enough. The NCBI physiology review explains why carbohydrate and lipid oxidation yield different ratios, but a person’s measured breath ratio can also be altered by non-steady exercise and ventilation. That makes an RQ a useful clue rather than a perfect label saying “only fat” or “only carbohydrate”. Laboratory physiologists must match the measurement period and conditions before interpreting a change. The classroom calculation is the first step in that reasoning.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.6 Respiratory quotient and the gases used to calculate it.
Use the science
Two equal-length trials have the same oxygen uptake but different carbon dioxide output. Which has the higher RQ, and what cannot be concluded?
Explore a possible response
The trial with more carbon dioxide has the higher ratio. That alone does not prove exclusive use of one fuel, because mixed substrates and measurement conditions can affect the observed gases.
Explore the source
- Physiology of respiratory quotientNCBI Bookshelf
Same gases, different process
7A · Exam PracticeNHLBI’s lung pages describe oxygen entering the blood and carbon dioxide leaving. Use that only as the body-level movement of the gases that 7A produces and consumes. It…Specification 7.6Read & use the scienceClose article
Why this matters
NHLBI’s lung pages describe oxygen entering the blood and carbon dioxide leaving. Use that only as the body-level movement of the gases that 7A produces and consumes. It is not a mark scheme for chemiosmosis. 7.1–7.6: the cell pathway, not ventilation. A measured gas or ATP change cannot, on its own, identify every intermediate enzyme or show which step changed. This is an extension to the lesson, not another fact to memorise.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.6 Respiratory quotient and the gases used to calculate it.
Use the science
Which gas volume would you still need, besides carbon dioxide, before an RQ could be calculated from a breathing experiment?
Explore a possible response
Oxygen consumed in the same period. Carbon dioxide alone is not an RQ.
Explore the source
- NHLBI: how the lungs workUS National Heart, Lung, and Blood Institute
Sprain and strain are not the specification pair
7B · Tissues of the Skeletal SystemThe NHS distinguishes a sprain as a damaged ligament from a strain as a damaged muscle. That is clinical language for injuries. It does not replace 7.9. You…Specification 7.9Read & use the scienceClose article
Why this matters
The NHS distinguishes a sprain as a damaged ligament from a strain as a damaged muscle. That is clinical language for injuries. It does not replace 7.9. You still have to say how intact muscles, tendons, ligaments and bones produce movement. 7.9: tendons link muscle to bone, ligaments link bone to bone, and antagonistic muscles move the joint in opposite directions. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.9 Muscles, tendons, bones and ligaments in movement.
Use the science
Why is “a sprain means the flexor failed” a mix-up?
Explore a possible response
A sprain, on the NHS page, is a ligament injury. A flexor is a muscle that decreases the joint angle. Different structures.
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Go to the lesson: Tissues of the Skeletal System →A prosthetic joint still needs opposing pulls
7B · Tissues of the Skeletal SystemEngineers working on a prosthetic limb have tried to preserve an agonist–antagonist muscle pair, so the wearer can move a joint in both directions and receive position feedback.…Specification 7.9Read & use the scienceClose article
Why this matters
Engineers working on a prosthetic limb have tried to preserve an agonist–antagonist muscle pair, so the wearer can move a joint in both directions and receive position feedback. The research paper starts from the same mechanical fact as 7.9: a muscle pulls when it contracts; it cannot actively push the joint back. In a natural limb, tendons transfer those pulls to bones and ligaments help stabilise the joint. A prosthesis changes the hardware but still needs a way to control opposing actions. This is a design problem, not evidence that an artificial joint has all the properties of a biological one.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.9 Muscles, tendons, bones and ligaments in movement.
Use the science
Why would linking only one contracting muscle to a bidirectional prosthetic joint make control difficult?
Explore a possible response
One muscle can pull in one direction. Opposing movement needs another active force or a mechanical return, and without the paired muscle feedback, position control is poorer.
Explore the source
- The agonist–antagonist myoneural interfacePeer-reviewed research via NIH PubMed Central
A pulled muscle is not a labelled sarcomere
7B · What Is Muscle?The NHS calls a strain an overstretched or torn muscle. That tells you muscle is a tissue that can be injured. It does not describe multinucleate fibres, T-tubules…Specification 7.10(i)Read & use the scienceClose article
Why this matters
The NHS calls a strain an overstretched or torn muscle. That tells you muscle is a tissue that can be injured. It does not describe multinucleate fibres, T-tubules or Z lines. Keep the leaflet out of the structure answer. 7.10(i): know the fibre, the membrane system and the sarcomere. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway. This is an extension to the lesson, not another fact to memorise.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.10(i) Structure of a mammalian skeletal muscle fibre.
Use the science
Why does “I strained a ligament, so my Z lines tore” mix two lessons?
Explore a possible response
A ligament joins bone to bone. Z lines are inside a muscle sarcomere. A strain, if that is the word the NHS page is using, refers to the muscle, and still does not identify the ultrastructure.
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Go to the lesson: What Is Muscle? →A muscle fibre has machinery within machinery
7B · What Is Muscle?Structural biologists study how ordered actin and myosin filaments make a repeating contractile unit. Their review follows the molecular interaction through the sarcomere rather than treating “muscle” as…Specification 7.10(i)Read & use the scienceClose article
Why this matters
Structural biologists study how ordered actin and myosin filaments make a repeating contractile unit. Their review follows the molecular interaction through the sarcomere rather than treating “muscle” as a single rope. That distinction helps with the scale of 7.10: a whole muscle contains fibres, each fibre contains myofibrils, and the myofibrils contain repeated sarcomeres. A strain diagnosed in a clinic is an injury to tissue; it is not a direct picture of a T-tubule or a Z line. Researchers need imaging and biochemical methods to connect damage at one scale with impaired movement at another.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.10(i) Structure of a mammalian skeletal muscle fibre.
Use the science
If a micrograph shows disrupted Z lines, what level of muscle organisation is directly observed, and what further evidence would show a whole-joint effect?
Explore a possible response
The micrograph observes sarcomere organisation inside a fibre. Measuring force or movement of the muscle and joint would be needed to show the larger functional effect.
Explore the source
- The actin–myosin interaction in musclePeer-reviewed review via NIH PubMed Central
Endurance and injury are different conversations
7B · Different Types of Muscle FibreNHS pages on strains describe injured muscle. They do not sort people into fibre types or promise that exercise will convert one type into the other. Use the…Specification 7.10(ii)Read & use the scienceClose article
Why this matters
NHS pages on strains describe injured muscle. They do not sort people into fibre types or promise that exercise will convert one type into the other. Use the comparison in the lesson for 7.10. Leave training claims out of the required answer. 7.10(ii): structural and physiological differences, not a coaching programme. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.10(ii) Structural and physiological differences between fast and slow fibres.
Use the science
Why is “fast fibres are the ones that get strained” not a specification conclusion?
Explore a possible response
A strain is an injury category. Fast fibres fatigue sooner and use glycolysis, but the NHS injury page does not map strains onto fibre types. Do not add that link.
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Go to the lesson: Different Types of Muscle Fibre →Fibre types are a continuum, not a sports horoscope
7B · Different Types of Muscle FibreA research review describes human skeletal muscle fibres along a slow-to-fast continuum, with intermediate types as well as the familiar slow and fast labels. Slow fibres tend to…Specification 7.10(ii)Read & use the scienceClose article
Why this matters
A research review describes human skeletal muscle fibres along a slow-to-fast continuum, with intermediate types as well as the familiar slow and fast labels. Slow fibres tend to be more fatigue resistant; fast fibres can generate force rapidly but often tire sooner. Training can alter properties, yet the evidence does not support an easy social-media test that fixes a person’s future sport from one fibre percentage. The 7.10 comparison is a useful model of structure and physiology, but actual performance also depends on technique, training, oxygen delivery and many other factors. Researchers use muscle samples and protein measurements, not a quiz about favourite workouts.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.10(ii) Structural and physiological differences between fast and slow fibres.
Use the science
Why would a sprint result alone be weak evidence that a runner has a particular muscle-fibre distribution?
Explore a possible response
Sprint performance depends on many variables, including training and technique. A performance time is not a direct measurement of fibre type or its metabolic properties.
Explore the source
- Muscle fibre type transitions with exercise trainingPeer-reviewed review via NIH PubMed Central
Soreness is not a cross-bridge diagram
7B · How Muscles ContractNHS information on muscle strains describes torn or overstretched muscle. It does not set out troponin, tropomyosin or ATP hydrolysis. Do not explain a strain by “the A…Specification 7.11Read & use the scienceClose article
Why this matters
NHS information on muscle strains describes torn or overstretched muscle. It does not set out troponin, tropomyosin or ATP hydrolysis. Do not explain a strain by “the A band got shorter”. The A band does not get shorter in normal contraction either. 7.11: sliding filaments, calcium uncovering binding sites, ATP and ATPase. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.11 Sliding filament contraction and the roles of calcium, ATP and ATPase.
Use the science
A friend says the A band shortens because the muscle is sore. What does the sliding filament evidence actually say about the A band?
Explore a possible response
The A band stays the same length because myosin filaments do not shorten. Soreness is not evidence about band length.
Explore the source
Go to the lesson: How Muscles Contract →Why a stopped ATP supply stiffens muscle
7B · How Muscles ContractA molecular review of actin–myosin interaction explains a counterintuitive part of contraction: ATP binding helps a myosin head detach from actin, while ATP hydrolysis prepares another force-producing cycle.…Specification 7.11Read & use the scienceClose article
Why this matters
A molecular review of actin–myosin interaction explains a counterintuitive part of contraction: ATP binding helps a myosin head detach from actin, while ATP hydrolysis prepares another force-producing cycle. When ATP production ceases after death, many attachments can remain, contributing to rigor mortis. This is a striking application of 7.11, but a living muscle does not work by staying in permanent rigor. Calcium still controls access to actin, and repeated attachment and detachment generate movement. The example also links Topic 7 to forensic science without making post-mortem timing an extra requirement for the muscle lesson.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.11 Sliding filament contraction and the roles of calcium, ATP and ATPase.
Use the science
Why would removing ATP stop both repeated shortening and normal relaxation?
Explore a possible response
Myosin needs ATP binding to detach from actin and ATP hydrolysis to reset for another cycle. Without ATP, cross-bridges can remain attached and cycles cannot continue.
Explore the source
- The actin–myosin interaction in musclePeer-reviewed review via NIH PubMed Central
An ECG records rhythm, it does not finish the medicine
7B · Cardiac Muscle and Control of the HeartbeatThe NHS describes an electrocardiogram as a test that records the electrical activity of the heart, including rate and rhythm, and that can be used when an abnormal…Specification 7.12(i)Read & use the scienceClose article
Why this matters
The NHS describes an electrocardiogram as a test that records the electrical activity of the heart, including rate and rhythm, and that can be used when an abnormal rhythm is suspected. That matches 7.12(iii). It is not an invitation to interpret a real trace, and it does not replace the SAN–AVN order you still have to write. 7.12: myogenic conduction through SAN, AVN, bundle of His and Purkyne fibres; an ECG can help identify an abnormal rhythm.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(i) Myogenic nature of cardiac muscle.
Use the science
Why is a faster heart rate on an ECG not automatically a damaged AVN?
Explore a possible response
Rate can change because the SAN is speeding up under nervous or hormonal control, which is normal in activity. An AVN problem is about delay or block between atria and ventricles. Speed alone does not locate the fault.
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Go to the lesson: Cardiac Muscle and Control of the Heartbeat →A pacemaker assists a conduction system
7B · Cardiac Muscle and Control of the HeartbeatThe NHLBI explains that an implanted pacemaker can send low-energy electrical pulses when a heartbeat is too slow or a signal is blocked. It does not create an…Specification 7.12(ii)Read & use the scienceClose article
Why this matters
The NHLBI explains that an implanted pacemaker can send low-energy electrical pulses when a heartbeat is too slow or a signal is blocked. It does not create an entirely new biological conduction pathway. The ordinary sequence still begins at the sinoatrial node, passes to the atrioventricular node, and reaches the ventricles through the bundle of His and Purkyne fibres. Clinicians use an ECG and other evidence to decide what kind of rhythm problem exists before choosing a device. The device is an application of electrical coordination, not a substitute for describing the myogenic origin of a normal beat.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(ii) Electrical coordination through the cardiac conduction pathway.
Use the science
Why might a signal block between atria and ventricles change their timing even if the sinoatrial node still fires?
Explore a possible response
The atrial impulse begins normally but does not reach the ventricles through the usual conduction route at the right time. Their contractions may become delayed or uncoordinated.
Explore the source
- Pacemakers: how they workUS National Heart, Lung, and Blood Institute
Heat illness is failed balance, not a new definition
7B · Principles of HomeostasisThe NHS distinguishes heat exhaustion, with heavy sweating, from heatstroke, a medical emergency in which the body is dangerously overheated and sweating may have stopped. That is what…Specification 7.16(ii)Read & use the scienceClose article
Why this matters
The NHS distinguishes heat exhaustion, with heavy sweating, from heatstroke, a medical emergency in which the body is dangerously overheated and sweating may have stopped. That is what it looks like when temperature is no longer held in a safe range. It is not the list of thermoregulatory effectors, and it is not advice you should turn into a first-aid essay in the exam. 7.16: negative feedback is what normally keeps a variable inside narrow limits. If the disturbance is too large, the limits are left.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.16(ii) Negative feedback maintains variables within narrow limits.
Use the science
Why is heatstroke not an example of successful negative feedback?
Explore a possible response
Successful negative feedback would increase heat loss and bring temperature back down. Heatstroke is the situation in which that control has been overwhelmed. It is a medical emergency on the NHS page, not a model answer for a healthy loop.
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Go to the lesson: Principles of Homeostasis →Feedback is measured over time
7B · Principles of HomeostasisA physiological control system can be recognised by a time series: a disturbance changes a variable, sensors detect it, and responses tend to bring it back toward a…Specification 7.16(ii)Read & use the scienceClose article
Why this matters
A physiological control system can be recognised by a time series: a disturbance changes a variable, sensors detect it, and responses tend to bring it back toward a range. That does not mean the graph is flat. The NIH account of the hypothalamus and pituitary describes multiple feedback signals, reminding us that a real body has interacting loops rather than a single cartoon arrow. For 7.16, identify the variable and the response before calling it negative feedback. An oscillation around a narrow range may be normal; a graph that drifts away after each response suggests the control is not compensating.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.16(ii) Negative feedback maintains variables within narrow limits.
Use the science
A graph shows temperature rising, then falling after sweating increases. What extra pattern would support negative feedback rather than coincidence?
Explore a possible response
Repeated disturbances followed by compensating responses and return toward a narrow range would support the feedback interpretation. One rise and fall alone is less persuasive.
Explore the source
- Functional anatomy of the hypothalamus and pituitaryEndotext, NCBI Bookshelf
Activity changes the rate; the node still starts the beat
7B · Controlling the Heart and Breathing RatesThe British Heart Foundation describes the heartbeat as starting at the sinoatrial node, and the pace as changing with activity and emotion. That supports the split you need:…Specification 7.13(i)Read & use the scienceClose article
Why this matters
The British Heart Foundation describes the heartbeat as starting at the sinoatrial node, and the pace as changing with activity and emotion. That supports the split you need: the SAN is the origin, and the rate is adjustable. Their page does not set out adrenaline or the medulla by name, so do not pretend it lists 7.14. 7.13 and 7.14: cardiac output, medullary control of rate, and adrenaline in fight or flight.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.13(i) Calculate cardiac output.
Use the science
Why is “the BHF says adrenaline is the pacemaker” an over-reading?
Explore a possible response
The page describes the sinoatrial node starting the signal and the pace changing with activity. Adrenaline is a specification hormone that modifies rate. It is not the pacemaker, and it is not a claim you should paste onto that page.
Explore the source
- British Heart Foundation: how a healthy heart worksBritish Heart Foundation
Stress hormones are measurable chemistry
7B · Controlling the Heart and Breathing RatesMedlinePlus describes catecholamines, including epinephrine or adrenaline, as hormones released during physical or emotional stress. Their effects include increased heart rate and blood flow to muscles. A clinician…Specification 7.14Read & use the scienceClose article
Why this matters
MedlinePlus describes catecholamines, including epinephrine or adrenaline, as hormones released during physical or emotional stress. Their effects include increased heart rate and blood flow to muscles. A clinician can measure catecholamines in blood or urine, but one high value needs context because stress, timing and other causes matter. The connection to 7.14 is a blood-borne signal that changes an organ’s activity; the sinoatrial node remains the origin of a normal heartbeat. A faster pulse is therefore not proof that adrenaline alone caused it, and it is not evidence that the medulla oblongata has stopped controlling rate.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.14 Adrenaline in the fight-or-flight response.
Use the science
How can adrenaline increase heart rate without becoming the heart’s pacemaker?
Explore a possible response
Adrenaline changes the rate at which pacemaker cells fire and affects cardiac activity. The sinoatrial node remains the source of the normal initiating electrical impulse.
Explore the source
- Catecholamine testsUS National Library of Medicine
Spirometry on the NHS is not this trace
7B · The Response of the Breathing System to ExerciseThe NHS describes spirometry as a test of how much air you can breathe out, used to check lung function. That is a forced clinical measurement. Core Practical…Specification 7.15Read & use the scienceClose article
Why this matters
The NHS describes spirometry as a test of how much air you can breathe out, used to check lung function. That is a forced clinical measurement. Core Practical data in this course are about tidal breathing, minute ventilation and oxygen consumption from a trace. Do not copy FEV numbers into a tidal-volume answer. The existence of the clinical test is only a warning about the name. 7.13 and 7.15: ventilation changes in exercise, read as tidal volume, rate, minute ventilation and oxygen consumption.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.15 Exercise and spirometer measurements of ventilation and oxygen use.
Use the science
Why does “the NHS spirometry result is the oxygen slope” fail?
Explore a possible response
That test measures a forced blow to assess lung function. The oxygen slope comes from a trace where carbon dioxide is absorbed and the volume falls as oxygen is used. Different method, different number.
Explore the source
Go to the lesson: The Response of the Breathing System to Exercise →The exercise mask measures more than a breath count
7B · The Response of the Breathing System to ExerciseA cardiopulmonary exercise laboratory can combine an ECG, blood pressure and exhaled-gas analysis while a person exercises. NHLBI describes this as a way to assess heart and lung…Specification 7.15Read & use the scienceClose article
Why this matters
A cardiopulmonary exercise laboratory can combine an ECG, blood pressure and exhaled-gas analysis while a person exercises. NHLBI describes this as a way to assess heart and lung function together. A school spirometer trace in 7.15 gives tidal volume, breathing rate and minute ventilation; gas analysis adds another measurement of oxygen use. More equipment does not make every inference automatic: a low oxygen uptake might arise from several limitations, and the clinical test needs trained interpretation. The useful school habit is to name what was actually measured before calculating a rate or explaining a change.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.15 Exercise and spirometer measurements of ventilation and oxygen use.
Use the science
A spirometer trace gives tidal volume and breathing frequency. What can you calculate, and what would require an additional gas measurement?
Explore a possible response
You can calculate respiratory minute ventilation by multiplying tidal volume by breathing frequency. Oxygen consumption needs information about the oxygen in inhaled and exhaled gas, not just volume.
Explore the source
- Pulmonary function testsUS National Heart, Lung, and Blood Institute
The clinical category is broader than one wave
7B · Thinking BiggerThe NHS arrhythmia page treats abnormal rhythm as a health topic with several patterns and several possible experiences, from noticeable palpitations to rhythms found on a test. That…Specification 7.12(iii)Read & use the scienceClose article
Why this matters
The NHS arrhythmia page treats abnormal rhythm as a health topic with several patterns and several possible experiences, from noticeable palpitations to rhythms found on a test. That variety is the enrichment. Required recall is still the conduction pathway and the idea that an ECG can help. Do not memorise the page’s symptom list as specification content. 7.12(iii): electrocardiograms can aid diagnosis of abnormal heart rhythms. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(iii) How ECGs aid diagnosis of abnormal heart rhythms.
Use the science
Why would revising only the letters P, QRS and T leave you short of this enrichment, and why would revising the NHS symptom list leave you short of the specification?
Explore a possible response
The letters describe a normal trace; the enrichment is that real rhythms can be abnormal in more than one way. The specification still wants SAN, AVN, bundle of His, Purkyne fibres and the principle of the ECG, not a copied symptom catalogue.
Explore the source
Go to the lesson: Thinking Bigger →The recording aids a clinician
7B · Exam PracticeNHLBI describes an electrocardiogram as a recording of how fast the heart is beating and whether the rhythm is steady, including the timing of electrical impulses. Use that…Specification 7.12(iii)Read & use the scienceClose article
Why this matters
NHLBI describes an electrocardiogram as a recording of how fast the heart is beating and whether the rhythm is steady, including the timing of electrical impulses. Use that as the meaning of 7.12(iii). Do not treat a practice calculation of cardiac output as a reading from that test. 7.9–7.16: movement and control. The ECG is the electrical record, not the cardiac-output formula. An injury, symptom or whole-body performance result is not a direct image of a sarcomere or cardiac conduction pathway.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.12(iii) How ECGs aid diagnosis of abnormal heart rhythms.
Use the science
Cardiac output uses volume per beat. What does an ECG add that the formula does not contain?
Explore a possible response
The electrical pattern and whether the rhythm is regular. The formula needs heart rate and stroke volume. An ECG does not, by itself, give stroke volume.
Explore the source
- NHLBI: heart testsUS National Heart, Lung, and Blood Institute
Cells keep most genes quiet
7C · Homeostasis and HormonesMedlinePlus Genetics explains that cells express only some of their genes, and that transcription factors are proteins which bind DNA and raise or lower transcription when signals arrive.…Specification 7.22Read & use the scienceClose article
Why this matters
MedlinePlus Genetics explains that cells express only some of their genes, and that transcription factors are proteins which bind DNA and raise or lower transcription when signals arrive. That is the general idea behind 7.22. The page does not classify peptide and steroid hormones, so the extracellular versus intracellular contrast still has to come from the specification. 7.22: transcription factors switch genes, peptide hormones act from outside the cell, and steroid hormones act inside.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.22 Transcription factors and peptide versus steroid hormone action.
Use the science
Why is “every cell uses every gene, and hormones only add energy” inconsistent with this source and with 7.22?
Explore a possible response
Cells transcribe a fraction of their genes. Hormones in this lesson change transcription through transcription factors. They are not a general energy drink, and peptide hormones do not even enter the cell.
Explore the source
- MedlinePlus Genetics: can genes be turned on and off?US National Library of Medicine
A steroid signal reaches the transcription machinery
7C · Homeostasis and HormonesA molecular review describes nuclear receptors as transcription factors whose activity can change when they bind steroid hormones. That is a concrete extension of 7.22: a lipid-soluble signal…Specification 7.22Read & use the scienceClose article
Why this matters
A molecular review describes nuclear receptors as transcription factors whose activity can change when they bind steroid hormones. That is a concrete extension of 7.22: a lipid-soluble signal can cross a cell membrane and influence which genes are transcribed. It does not mean every steroid binds DNA directly or that every hormone uses the same receptor. Peptide hormones usually act through surface receptors and intracellular signalling before transcription changes. Researchers can compare RNA production before and after hormone exposure, but that measurement alone still needs controls to show which receptor and promoter are responsible.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.22 Transcription factors and peptide versus steroid hormone action.
Use the science
Why can a steroid hormone alter transcription even though it is not itself a transcription factor?
Explore a possible response
It can bind an intracellular receptor. The hormone–receptor complex, or a downstream factor it controls, can then regulate transcription at target genes.
Explore the source
- Signalling by nuclear receptorsPeer-reviewed review via NIH PubMed Central
Filter and reabsorb, then the specification adds the mechanism
7C · Osmoregulation in Mammals: The KidneyNIDDK describes kidneys as filtering blood, removing wastes such as urea and extra water, and returning water and nutrients the body still needs. It names the nephron, the…Specification 7.20Read & use the scienceClose article
Why this matters
NIDDK describes kidneys as filtering blood, removing wastes such as urea and extra water, and returning water and nutrients the body still needs. It names the nephron, the glomerulus and the tubule. That is the right public outline. It does not teach the afferent arteriole, the basement membrane, or the loop as a countercurrent multiplier. Those mechanisms stay in 7.18–7.20. 7.18–7.20: structure, urea and ultrafiltration, selective reabsorption, and the loop of Henle.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.20 Selective reabsorption and the loop of Henle.
Use the science
Why is “the tubule filters like a sieve” less precise than the specification?
Explore a possible response
The sieve-like pressure filter is the glomerulus. The tubule then reabsorbs useful solutes. Calling the whole tubule a sieve misses selective reabsorption and the multiplier.
Explore the source
- NIDDK: your kidneys and how they workUS National Institute of Diabetes and Digestive and Kidney Diseases
A dialyser is selective in a different way
7C · Osmoregulation in Mammals: The KidneyThe NIDDK describes haemodialysis as blood flowing through a filter while dialysis fluid moves on the other side. Waste solutes and excess water can leave the blood, but…Specification 7.20Read & use the scienceClose article
Why this matters
The NIDDK describes haemodialysis as blood flowing through a filter while dialysis fluid moves on the other side. Waste solutes and excess water can leave the blood, but the treatment replaces only part of kidney function. A nephron filters at the glomerulus and then selectively reabsorbs useful substances along its tubule; the loop of Henle helps build the medullary gradient for water conservation. A dialyser does not reconstruct that living countercurrent system. A renal specialist must adjust dialysis fluid and treatment conditions using measurements, which is why a “machine kidney” is an analogy with important limits.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.20 Selective reabsorption and the loop of Henle.
Use the science
Why would a dialyser that removes urea not automatically reproduce selective reabsorption in a healthy proximal tubule?
Explore a possible response
Removing a waste solute through a membrane is different from active, selective recovery of useful solutes into blood. The machine lacks the nephron’s living transport cells and countercurrent organisation.
Explore the source
- NIDDK: haemodialysisUS National Institute of Diabetes and Digestive and Kidney Diseases
A large urine volume can mean the hormone or the response
7C · Control of the Kidney and HomeostasisThe NHS describes diabetes insipidus as a problem with antidiuretic hormone, also called vasopressin. Either there is not enough hormone, or the kidneys do not respond to it.…Specification 7.21Read & use the scienceClose article
Why this matters
The NHS describes diabetes insipidus as a problem with antidiuretic hormone, also called vasopressin. Either there is not enough hormone, or the kidneys do not respond to it. People then pass large volumes of dilute urine and become very thirsty. That is enrichment. It is not a required disease, and it is not a reason to give treatment advice. It does show why “lots of urine” does not, by itself, name the broken step. 7.21: osmoreceptors, pituitary ADH, and kidney water reabsorption in negative feedback.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.21 ADH, hypothalamus and pituitary in water-balance feedback.
Use the science
Why would treating both causes as “the pituitary failed” be inaccurate?
Explore a possible response
One cause is a lack of ADH. The other is a kidney that does not respond even if ADH is present. The NHS page separates those. The feedback diagram only works if both the release and the duct response occur.
Explore the source
Go to the lesson: Control of the Kidney and Homeostasis →Same urine result, two different faults
7C · Control of the Kidney and HomeostasisNIDDK distinguishes central diabetes insipidus, in which too little vasopressin or ADH is produced, from nephrogenic disease, in which the kidneys do not respond properly to it. Both…Specification 7.21Read & use the scienceClose article
Why this matters
NIDDK distinguishes central diabetes insipidus, in which too little vasopressin or ADH is produced, from nephrogenic disease, in which the kidneys do not respond properly to it. Both can cause large volumes of dilute urine. That is a powerful warning about feedback diagrams: the same final measurement can come from a problem with the signal or with the target. In 7.21, osmoreceptors in the hypothalamus, pituitary release of ADH and kidney water reabsorption form one control chain. The public health page explains the clinical categories; it does not let a student diagnose a person from urine volume alone.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.21 ADH, hypothalamus and pituitary in water-balance feedback.
Use the science
Why would measuring urine volume alone fail to distinguish low ADH secretion from poor kidney response to ADH?
Explore a possible response
Both mechanisms reduce water reabsorption and can produce a large urine volume. Hormone measurements or response tests are needed to locate the fault.
Explore the source
- Diabetes insipidusUS National Institute of Diabetes and Digestive and Kidney Diseases
Heat exhaustion is not an extra effector
7C · Thermoregulation and ExerciseThe NHS distinguishes heat exhaustion, with heavy sweating, from heatstroke, where the person is dangerously hot, the skin may be hot and dry, and emergency help is needed.…Specification 7.17Read & use the scienceClose article
Why this matters
The NHS distinguishes heat exhaustion, with heavy sweating, from heatstroke, where the person is dangerously hot, the skin may be hot and dry, and emergency help is needed. Use this only as the boundary of 7.17: negative feedback has a limited capacity. Do not turn the symptom list into required recall, and do not use this page as medical advice for a real person who is unwell. Seek urgent help for real heat illness. 7.17: the hypothalamus coordinates thermoregulation so exercise can continue in dynamic equilibrium.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.17 Homeostasis and thermoregulation during exercise.
Use the science
Why is “hot dry skin means vasodilation has succeeded” the wrong reading?
Explore a possible response
Successful heat loss includes sweating. Hot dry skin, in the NHS contrast, fits heatstroke, where sweating has failed and the situation is an emergency. Vasodilation alone is not success if evaporative cooling has stopped and temperature is still rising.
Explore the source
Go to the lesson: Thermoregulation and Exercise →Heat stress is a failure of balance, not a thermometer fact
7C · Thermoregulation and ExerciseCDC guidance describes heat-related illness when the body cannot keep temperature controlled under a high heat load. Exercise adds metabolic heat while hot or humid air can limit…Specification 7.17Read & use the scienceClose article
Why this matters
CDC guidance describes heat-related illness when the body cannot keep temperature controlled under a high heat load. Exercise adds metabolic heat while hot or humid air can limit heat loss. The 7.17 idea of dynamic equilibrium explains why the hypothalamus must coordinate responses such as sweating and changes in skin blood flow. It does not imply that a body holds one exact number at every moment. A rise in core temperature is an observation; interpreting the cause requires information about workload, environment, hydration and the effectiveness of heat-loss responses. This is especially relevant for outdoor work and sport.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.17 Homeostasis and thermoregulation during exercise.
Use the science
Why can very humid air make sweating less effective even when the hypothalamus increases sweat production?
Explore a possible response
Evaporation carries heat away. Humid air reduces the rate at which sweat evaporates, so producing more sweat may not remove enough heat to maintain the usual temperature range.
Explore the source
- Heat-related illnessesUS Centers for Disease Control and Prevention
Haemodialysis is not a second nephron
7C · Thinking BiggerNIDDK explains that haemodialysis filters wastes and extra fluid outside the body using a dialyser, and that this replaces only part of what healthy kidneys do. It is…Specification 7.20Read & use the scienceClose article
Why this matters
NIDDK explains that haemodialysis filters wastes and extra fluid outside the body using a dialyser, and that this replaces only part of what healthy kidneys do. It is not a cure. Use it to see the difference between clearing blood and the full specification nephron. Do not use it to advise anyone about treatment. 7.18–7.20: structure, ultrafiltration and selective reabsorption are still the required biology. A clinical observation reflects a working control system, but does not isolate one nephron, hormone or transcription factor without further evidence.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.20 Selective reabsorption and the loop of Henle.
Use the science
Why does a good dialysis summary not earn the countercurrent-multiplier mark by itself?
Explore a possible response
The multiplier is the loop of Henle building a medullary salt gradient. An external filter removing fluid is a different process. The source describes that filter, not the loop.
Explore the source
- NIDDK: haemodialysisUS National Institute of Diabetes and Digestive and Kidney Diseases
The public filter is the start of the answer
7C · Exam PracticeNIDDK’s overview says kidneys filter wastes, including urea, and return substances the body needs. Use that sentence as a check that your longer answer has not put urea…Specification 7.18Read & use the scienceClose article
Why this matters
NIDDK’s overview says kidneys filter wastes, including urea, and return substances the body needs. Use that sentence as a check that your longer answer has not put urea production in the kidney or left glucose in the urine as if that were normal. The page is not the countercurrent account. 7.17–7.22: hormones, kidney, ADH and thermoregulation. A clinical observation reflects a working control system, but does not isolate one nephron, hormone or transcription factor without further evidence.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 7.18 Gross and microscopic kidney structure.
Use the science
Which specification detail is still missing if an answer only says “the kidney filters urea and keeps useful nutrients”?
Explore a possible response
Any of: ultrafiltration under pressure at the glomerulus, selective reabsorption in the proximal tubule, the loop as a countercurrent multiplier, or ADH control of the collecting duct. The public sentence is true and incomplete.
Explore the source
- NIDDK: your kidneys and how they workUS National Institute of Diabetes and Digestive and Kidney Diseases
Light becomes a signal only after a receptor cell
8A · The Structure of NeuronesThe National Eye Institute describes the retina as a light-sensitive layer where photoreceptors turn light into electrical signals. That is the start of a sensory pathway. The page…Specification 8.1Read & use the scienceClose article
Why this matters
The National Eye Institute describes the retina as a light-sensitive layer where photoreceptors turn light into electrical signals. That is the start of a sensory pathway. The page does not name Schwann cells or the three neurone types. The specification structure is still yours to learn. Rod detail is a later lesson. 8.1: sensory neurones carry impulses that began at a receptor. Motor neurones end at an effector. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.1 Sensory, relay and motor neurones, Schwann cells and myelin.
Use the science
Why is “the eye is a motor neurone” a category error?
Explore a possible response
The eye contains receptors. A sensory neurone carries the impulse inward. A motor neurone would carry an impulse out to an effector. The NEI sentence is about detection, not about myelin.
Explore the source
- National Eye Institute: how the eyes workUS National Eye Institute
Myelin damage changes a network, not just one cable
8A · The Structure of NeuronesThe US neurological institute describes multiple sclerosis as immune injury to myelin in the central nervous system. Myelin insulates parts of an axon and supports rapid signal conduction,…Specification 8.1Read & use the scienceClose article
Why this matters
The US neurological institute describes multiple sclerosis as immune injury to myelin in the central nervous system. Myelin insulates parts of an axon and supports rapid signal conduction, so damage can disrupt communication across sensory and motor pathways. Your 8.1 diagram includes Schwann cells, which myelinate peripheral axons; central myelin is made by oligodendrocytes. That distinction matters because MS affects the central system. Symptoms depend on which pathways are injured, not on one fixed sketch of a damaged sheath. Clinicians combine history, examination and imaging because the biology occurs in a network, not in an isolated textbook neurone.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.1 Sensory, relay and motor neurones, Schwann cells and myelin.
Use the science
Why might myelin damage produce a sensory problem in one person and a movement problem in another?
Explore a possible response
The effect depends on where the damage lies. Disrupting sensory pathways changes information reaching the CNS; disrupting motor pathways changes signals sent to effectors.
Explore the source
- Multiple sclerosis: hope through researchUS National Institute of Neurological Disorders and Stroke
A receptor starts the pathway the cord then finishes
8A · How the Nervous System WorksThe National Eye Institute describes photoreceptors turning light into electrical signals. A spinal reflex uses the same idea of a receptor, then neurones, then an effector, but the…Specification 8.2Read & use the scienceClose article
Why this matters
The National Eye Institute describes photoreceptors turning light into electrical signals. A spinal reflex uses the same idea of a receptor, then neurones, then an effector, but the worked example is the cord, not the eye. Do not move the pupil reflex into the grey matter of the spine. 8.2 and 8.3: a stimulus leads to an effector response, and a spinal reflex does that through grey matter. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.2 Nervous responses from stimulus to effector.
Use the science
Why is blinking in bright light a poor diagram for 8.3?
Explore a possible response
8.3 is a spinal arc, with grey and white matter of the cord. The pupil and many eye reflexes are coordinated in the brain. Use a withdrawal from the skin if you need the spinal list.
Explore the source
- National Eye Institute: how the eyes workUS National Eye Institute
After spinal injury, signal direction matters
8A · How the Nervous System WorksNINDS describes the spinal cord as the route that sends and receives signals between brain and body. An injury can interrupt sensory information travelling in and motor commands…Specification 8.2Read & use the scienceClose article
Why this matters
NINDS describes the spinal cord as the route that sends and receives signals between brain and body. An injury can interrupt sensory information travelling in and motor commands travelling out, though the effects depend strongly on its location and extent. This applies the 8.2 stimulus-to-effector chain to rehabilitation: a therapist needs to know whether the difficulty is sensing a stimulus, processing it centrally or activating a muscle. A visible movement does not by itself show that every part of the original pathway is intact; local reflex circuits can still act in some circumstances.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.2 Nervous responses from stimulus to effector.
Use the science
Why would the loss of voluntary movement below a spinal injury not prove that every local reflex arc below it is destroyed?
Explore a possible response
Voluntary commands from the brain may be interrupted while sensory, relay and motor neurones in a local spinal circuit remain connected. Reflex behaviour needs separate testing.
Explore the source
- Spinal cord injuryUS National Institute of Neurological Disorders and Stroke
A receptor potential is not yet this spike
8A · The Neurones in ActionThe National Eye Institute says photoreceptors turn light into electrical signals. In a rod, that first electrical event is a hyperpolarisation, taught in the sensory lesson, not the…Specification 8.4Read & use the scienceClose article
Why this matters
The National Eye Institute says photoreceptors turn light into electrical signals. In a rod, that first electrical event is a hyperpolarisation, taught in the sensory lesson, not the sodium spike drawn here. Action potentials appear later, in the optic neurones. Use the eye page as a warning not to give every cell the same curve. 8.4 and 8.5: sodium and potassium permeabilities make the spike, and myelin makes it saltatory.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.4 Action potentials and sodium/potassium permeability.
Use the science
Why is “light opens sodium channels in the rod, like an axon” the wrong transfer of this lesson?
Explore a possible response
In an axon, sodium entry depolarises and makes the spike. In a rod, light leads to sodium channels closing and the cell hyperpolarises. The optic neurone is where the action-potential story applies.
Explore the source
- National Eye Institute: how the eyes workUS National Eye Institute
A local anaesthetic tests the sodium step
8A · The Neurones in ActionThe National Cancer Institute drug dictionary describes lidocaine as interacting with voltage-gated sodium channels and reducing the transient rise in membrane permeability to sodium. That is the rising…Specification 8.4Read & use the scienceClose article
Why this matters
The National Cancer Institute drug dictionary describes lidocaine as interacting with voltage-gated sodium channels and reducing the transient rise in membrane permeability to sodium. That is the rising phase of the action potential in 8.4. Blocking it can prevent an impulse from passing through the treated nerve, which is useful in local anaesthesia. The drug is an application, not a new version of the resting-potential diagram. Sodium-channel block does not mean potassium channels have vanished or that every sensory receptor is inactive. A nerve can detect a stimulus yet fail to conduct the resulting signal onward.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.4 Action potentials and sodium/potassium permeability.
Use the science
Why can a receptor still detect a stimulus while lidocaine prevents the person from feeling it?
Explore a possible response
Detection at the receptor and propagation along the sensory axon are distinct steps. Lidocaine blocks sodium-dependent action potentials, so the signal may not reach the CNS.
Explore the source
- Lidocaine hydrochloride: drug definitionUS National Cancer Institute
The NHS account of Parkinson’s is the cell loss
8A · The Effect of Drugs on the Nervous SystemThe NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement…Specification 8.7Read & use the scienceClose article
Why this matters
The NHS says Parkinson’s disease is caused by a loss of nerve cells in the substantia nigra, which reduces dopamine, and that people may have tremor, slow movement and stiff muscles. That supports the reason L-DOPA exists in the specification. The page is a health overview. It is not a dose chart, and it does not describe nicotine, lidocaine or MDMA. 8.7: L-DOPA is used because dopamine signalling has fallen. The other four substances are different synaptic or channel effects.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Why is “the NHS says take L-DOPA with MDMA” an unacceptable sentence?
Explore a possible response
The NHS page describes the disease, not a combination with MDMA. MDMA is not a treatment. This lesson only explains mechanisms. Medical decisions belong with a clinician, not a revision note.
Explore the source
Go to the lesson: The Effect of Drugs on the Nervous System →One receptor, very different chemicals
8A · The Effect of Drugs on the Nervous SystemAn NCBI neuroscience chapter describes the nicotinic acetylcholine receptor as a ligand-gated channel that can bind acetylcholine, nicotine and certain toxins. That helps explain why substances with very…Specification 8.7Read & use the scienceClose article
Why this matters
An NCBI neuroscience chapter describes the nicotinic acetylcholine receptor as a ligand-gated channel that can bind acetylcholine, nicotine and certain toxins. That helps explain why substances with very different origins can interfere at a synapse: they interact with the same protein but do not necessarily cause the same response. A toxin that prevents receptor activation can stop the usual postsynaptic change, while an agonist can mimic part of the neurotransmitter’s effect. The 8.7 examples require mechanism, not a list of frightening names. Concentration, receptor location and exposure route also matter for any real-world effect.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Why would a toxin that blocks acetylcholine binding at a neuromuscular junction weaken muscle contraction?
Explore a possible response
The motor neurone can release acetylcholine, but the postsynaptic receptor cannot be activated normally. The muscle fibre receives a weaker or absent signal to begin contraction.
Explore the source
- Cholinergic receptorsNeuroscience, NCBI Bookshelf
Photoreceptors start the electrical story
8A · Sensory Systems and the Detection of LightThe National Eye Institute says the retina is a light-sensitive layer and that photoreceptors turn light into electrical signals. It does not mention rhodopsin, retinal, or hyperpolarisation. Those…Specification 8.8Read & use the scienceClose article
Why this matters
The National Eye Institute says the retina is a light-sensitive layer and that photoreceptors turn light into electrical signals. It does not mention rhodopsin, retinal, or hyperpolarisation. Those names are the specification. Use the page only to remember that the eye’s job is a signal, then write the rod mechanism properly. 8.8: rhodopsin, closing of sodium channels, hyperpolarisation, then action potentials in optic neurones. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.8 Rod cells, rhodopsin and visual signalling.
Use the science
Why is an answer that only says “the retina detects light” short of 8.8?
Explore a possible response
It misses opsin and retinal, the closing of sodium channels, hyperpolarisation of the rod, and the fact that the spikes are in the optic neurones.
Explore the source
- National Eye Institute: how the eyes workUS National Eye Institute
Dark adaptation is more than pupil size
8A · Sensory Systems and the Detection of LightNEI researchers studied how rod photoreceptors in mice adjust their sensitivity when light conditions change. Rods are especially useful in dim light, and the study followed movement of…Specification 8.8Read & use the scienceClose article
Why this matters
NEI researchers studied how rod photoreceptors in mice adjust their sensitivity when light conditions change. Rods are especially useful in dim light, and the study followed movement of a signalling protein called transducin inside those cells. This is beyond the required rhodopsin–retinal–channel sequence, but it reinforces that vision changes within the retina as well as at the pupil. A dilated pupil lets more light reach the retina; it does not itself restore the molecular state of a bleached pigment or explain every minute of dark adaptation. The mouse result is a research clue, not a direct measurement of one student’s night vision.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.8 Rod cells, rhodopsin and visual signalling.
Use the science
Why could two eyes with equally wide pupils still differ in sensitivity to dim light?
Explore a possible response
Pupil diameter controls light entry, but the state and number of rod photoreceptors and their signalling machinery determine how that light is converted to neural signals.
Explore the source
- How eyes adapt to the darkUS National Eye Institute
The eye page names detection, not the iris muscles
8A · Synapses and HabituationThe National Eye Institute describes photoreceptors creating electrical signals from light. Brightness is the stimulus for the pupil reflex as well as for rods. The page does not…Specification 8.6(ii)Read & use the scienceClose article
Why this matters
The National Eye Institute describes photoreceptors creating electrical signals from light. Brightness is the stimulus for the pupil reflex as well as for rods. The page does not describe circular and radial muscles or acetylcholine. Those belong to 8.6. 8.6 and 8.9: synaptic transmission, pupil size, and habituation. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.6(ii) Pupil dilation and constriction.
Use the science
Why is “the retina is the muscle that constricts the pupil” incorrect?
Explore a possible response
The retina detects light. The effectors are the iris muscles. Neurones and synapses join the two. A photoreceptor is not the muscle.
Explore the source
- National Eye Institute: how the eyes workUS National Eye Institute
A sea slug taught neuroscientists about habituation
8A · Synapses and HabituationEric Kandel’s Nobel account describes work with the sea slug Aplysia. Repeated harmless touch to its gill-withdrawal system could lead to a weaker response: habituation. The research linked…Specification 8.9Read & use the scienceClose article
Why this matters
Eric Kandel’s Nobel account describes work with the sea slug Aplysia. Repeated harmless touch to its gill-withdrawal system could lead to a weaker response: habituation. The research linked this behavioural change to altered effectiveness at specific synapses. That is a more precise idea than “the animal got bored”, because the stimulus still arrives but the pathway responds differently. The Aplysia model is an enrichment example, not proof that all human learning is one synapse. It also helps separate habituation from sensory adaptation: in habituation, the nervous system changes its response to a repeated, non-threatening input.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.9 Habituation to a repeated stimulus.
Use the science
If the sensory receptor still responds to each touch but the gill withdraws less, why is a changed synapse a plausible explanation?
Explore a possible response
The input is still detected, so a weaker output may arise where the sensory signal is passed to the next neurone or motor pathway. The conclusion needs pathway evidence, not behaviour alone.
Explore the source
- Eric Kandel: research on Aplysia habituationNobel Prize Outreach
Dopamine loss is not an axon sodium story
8A · Exam PracticeThe NHS account of Parkinson’s is loss of substantia nigra cells and reduced dopamine, with effects on movement. That is an 8.7 synapse problem. It is not a…Specification 8.7Read & use the scienceClose article
Why this matters
The NHS account of Parkinson’s is loss of substantia nigra cells and reduced dopamine, with effects on movement. That is an 8.7 synapse problem. It is not a failure of myelin or of rod pigment. Do not treat the health page as a drug list. 8.1–8.9 reviewed as structures and transmission. A behaviour or symptom is the output of a pathway, not a direct recording of ion movement in one axon or synapse.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.7 How specified drugs alter nerve impulse transmission.
Use the science
Which named substance in 8.7 is the one linked to that cell loss, and what does it become?
Explore a possible response
L-DOPA. It can cross into the brain and be converted to dopamine. It does not restore the missing cells.
Explore the source
Go to the lesson: Exam Practice →MRI is one way the living brain is pictured
8B · The Central Nervous SystemNIBIB describes MRI as using magnets and radio waves to picture soft tissues, including the brain and spinal cord, without ionising radiation. It also names fMRI as a…Specification 8.10Read & use the scienceClose article
Why this matters
NIBIB describes MRI as using magnets and radio waves to picture soft tissues, including the brain and spinal cord, without ionising radiation. It also names fMRI as a way to watch brain activation during a task. That is context for why the central nervous system can be studied in a living person. The scan names are 8B 3. This page only needs the organs that count as central. 8.10 and 8.13: brain plus cord, and nervous versus hormonal coordination.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.10 Central and peripheral nervous systems.
Use the science
Why is an MRI picture not itself the definition of the central nervous system?
Explore a possible response
The definition is anatomical: brain and spinal cord. A scan is a way to look at those organs. Peripheral nerves are still outside the definition even if a picture shows one of them.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
The hypothalamus links two kinds of control
8B · The Central Nervous SystemAn Endotext review describes the hypothalamus as a small brain region that connects neural information with pituitary hormone control and wider homeostatic responses. That makes it a useful…Specification 8.13Read & use the scienceClose article
Why this matters
An Endotext review describes the hypothalamus as a small brain region that connects neural information with pituitary hormone control and wider homeostatic responses. That makes it a useful real example of 8.13: nervous signalling can be rapid and targeted while hormones travel through blood and often act over longer times. The two systems interact rather than operating as rival control rooms. Locating the hypothalamus on a brain diagram is only the start; a researcher must ask what signal arrives, which cells release a hormone and what target responds. A scan of its position would not by itself show all those steps.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.13 Nervous and hormonal coordination in animals.
Use the science
Why can a neural input to the hypothalamus produce a response in an organ that is not directly connected to that neurone?
Explore a possible response
The hypothalamus can alter hormone release through the pituitary. The hormone then travels in blood to a distant target with the appropriate receptor.
Explore the source
- Functional anatomy of the hypothalamus and pituitaryEndotext, NCBI Bookshelf
A scan can show the centre the nerves plug into
8B · The Peripheral Nervous SystemNIBIB’s MRI description includes the spinal cord as a soft tissue that can be pictured without ionising radiation. A spinal nerve leaving that cord is the peripheral part.…Specification 8.10Read & use the scienceClose article
Why this matters
NIBIB’s MRI description includes the spinal cord as a soft tissue that can be pictured without ionising radiation. A spinal nerve leaving that cord is the peripheral part. The page does not define somatic and autonomic paths. Use it to keep “what we can picture” separate from “how the pathways are classified”. 8.10: peripheral nerves connect receptors and effectors to the brain and spinal cord. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.10 Central and peripheral nervous systems.
Use the science
Why is “the MRI is the peripheral nervous system” wrong?
Explore a possible response
An MRI is a picture. The peripheral nervous system is the nerves and ganglia outside the brain and cord. The cord itself, even on a clear scan, is central.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
A peripheral nerve test asks where the fault lies
8B · The Peripheral Nervous SystemNINDS describes peripheral neuropathy as damage to nerves outside the brain and spinal cord. Clinicians may use nerve-conduction studies to estimate how strongly and quickly signals pass along…Specification 8.10Read & use the scienceClose article
Why this matters
NINDS describes peripheral neuropathy as damage to nerves outside the brain and spinal cord. Clinicians may use nerve-conduction studies to estimate how strongly and quickly signals pass along some peripheral nerves. This shows why the 8.10 distinction between central and peripheral systems matters beyond a labelled diagram: a problem in an arm nerve is not the same location as one in the spinal cord or brain. A slow test result still needs interpretation; it cannot identify every cause from conduction speed alone. Sensory and motor fibres may be affected differently, so symptoms and measurements should be compared.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.10 Central and peripheral nervous systems.
Use the science
Why would normal brain imaging not rule out a problem in a peripheral sensory nerve?
Explore a possible response
The nerve lies outside the brain and spinal cord. A brain image does not directly test conduction along that peripheral pathway.
Explore the source
- Peripheral neuropathyUS National Institute of Neurological Disorders and Stroke
Activation during a task is not a thought transcript
8B · Investigating the Human BrainNIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for 8.15’s functional MRI. It does not say the scanner reads intentions. CT and PET are separate NHS descriptions: X-rays, and a radioactive tracer. 8.14 and 8.15: know the five regions, and know what each scan can show. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Why is “the fMRI showed the hypothalamus, so the person was thirsty” too strong?
Explore a possible response
Seeing a region, or even activation, is not a labelled thirst. Thirst would be an interpretation that needs the task and other evidence. The hypothalamus does contain water-balance centres, but a scan caption is not that conclusion by itself.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
PET traces molecules, not thoughts
8B · Investigating the Human BrainNIBIB explains that PET imaging uses a radioactive tracer whose distribution can be detected to investigate function in a living body. That is a different measurement from the…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB explains that PET imaging uses a radioactive tracer whose distribution can be detected to investigate function in a living body. That is a different measurement from the structural x-ray slices of CT or the magnetic signals of MRI. For 8.15, the distinction matters more than the colours on a scan: each technique turns a physical signal into an image with limits and uncertainty. A bright PET region is not a transcript of a person’s thoughts. Researchers or clinicians must know which tracer was used, when the measurement was made and what comparison is appropriate before interpreting a pattern.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Why might a PET image and an MRI image of the same brain answer different biological questions?
Explore a possible response
PET maps the distribution of a selected tracer and can reflect a function or biochemical process. MRI provides detailed structure; the signals and interpretations are different.
Explore the source
- Nuclear medicine and PETUS National Institute of Biomedical Imaging and Bioengineering
Read the NHS sentence before you simplify depression
8B · The Chemical Balance of the BrainThe NHS describes depression as a low mood that can last a long time or keep returning and that affects everyday life. It does not, on that page,…Specification 8.16Read & use the scienceClose article
Why this matters
The NHS describes depression as a low mood that can last a long time or keep returning and that affects everyday life. It does not, on that page, say the cause is low serotonin. The specification separately says a serotonin imbalance can contribute, and that this kind of knowledge is used to develop drugs. Hold both. Do not tell someone that a revision note replaces care. 8.16: dopamine in Parkinson’s disease, serotonin in depression, and drug ideas that change transmission.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.16 Brain chemicals, ill health and drug development.
Use the science
Why would it be wrong to add “the NHS page says take a serotonin drug” to a 8.16 answer?
Explore a possible response
That page describes the condition. It does not set out a transmitter or a dose. Drug names and whether they are appropriate belong in clinical care, not in this sentence.
Explore the source
Go to the lesson: The Chemical Balance of the Brain →A depression headline is not a serotonin assay
8B · The Chemical Balance of the BrainNIMH presents depression as a condition with varied symptoms and causes, and explains that treatment decisions are clinical rather than the result of one simple chemical reading. Specification…Specification 8.16Read & use the scienceClose article
Why this matters
NIMH presents depression as a condition with varied symptoms and causes, and explains that treatment decisions are clinical rather than the result of one simple chemical reading. Specification 8.16 asks how imbalances in brain chemicals can contribute to ill health; “contribute” does not mean that every case has one measured serotonin deficit. Medicines affecting neurotransmission can help some people, but their effect does not prove a single-cause explanation for the condition. This is a useful test of a popular claim: a mechanism proposed for a drug and a complete explanation of a person’s illness are not the same thing.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.16 Brain chemicals, ill health and drug development.
Use the science
Why does improvement after a medicine that affects serotonin not prove that low serotonin was the sole cause of a person’s depression?
Explore a possible response
A treatment can change one pathway and improve symptoms in a complex condition. Response to treatment does not isolate a single original cause, and other biological and environmental factors can contribute.
Explore the source
- DepressionUS National Institute of Mental Health
A hormone can be the signal a transcription factor waits for
8B · Chemical Control Systems in PlantsMedlinePlus Genetics explains that signals can activate transcription factors, proteins that bind DNA and raise or lower transcription. It does not mention auxin or gibberellin. Those are the…Specification 8.11Read & use the scienceClose article
Why this matters
MedlinePlus Genetics explains that signals can activate transcription factors, proteins that bind DNA and raise or lower transcription. It does not mention auxin or gibberellin. Those are the plant signals in 8.11. The page is the general idea. The aleurone’s amylase gene is the plant example. 8.11: IAA and gibberellins cause responses that include changes in transcription. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why is “gibberellin cuts starch itself” inconsistent with a transcription-factor account?
Explore a possible response
Gibberellin is the signal. Transcription factors then change production of amylase. The enzyme, not the hormone, hydrolyses the starch.
Explore the source
- MedlinePlus Genetics: can genes be turned on and off?US National Library of Medicine
Plants read the colour of their neighbours
8B · Chemical Control Systems in PlantsPlants beneath leaves receive less red light relative to far-red light because neighbouring foliage changes the light spectrum. A research paper identified early gene-expression targets in Arabidopsis after…Specification 8.11Read & use the scienceClose article
Why this matters
Plants beneath leaves receive less red light relative to far-red light because neighbouring foliage changes the light spectrum. A research paper identified early gene-expression targets in Arabidopsis after phytochrome signalling during shade avoidance. This extends 8.11 from a textbook light switch to an environmental signal that can alter growth. Phytochrome does not push a stem mechanically; a signalling network changes transcription and hormone responses before cells elongate. The exact gene names in the paper are enrichment. To test whether the response is due to light quality rather than light quantity, an experiment must control both separately.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why would comparing plants under equal light intensity but different red:far-red ratios help test phytochrome signalling?
Explore a possible response
It holds total light intensity similar while changing the spectral cue phytochrome detects. A growth difference would then support an effect of light quality, though other controls are still needed.
Explore the source
- Primary target genes of phytochrome signallingPeer-reviewed research via NIH PubMed Central
Flowering is a transcription decision
8B · Phytochrome and FloweringMedlinePlus Genetics describes signals acting through transcription factors that bind DNA and change transcription. Phytochrome’s Pfr is such a signal in the plant, even though that human-genetics page…Specification 8.11Read & use the scienceClose article
Why this matters
MedlinePlus Genetics describes signals acting through transcription factors that bind DNA and change transcription. Phytochrome’s Pfr is such a signal in the plant, even though that human-genetics page never names it. The night-length rules on this page are how much Pfr the plant has. The next lesson is what Pfr does to genes. 8.11: phytochrome controls flowering responses. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why is a correct night-length answer still incomplete if it never mentions that Pfr is active?
Explore a possible response
The plant is not measuring darkness with a clock you can see. It is the amount of Pfr, which falls in a long night and is rebuilt by red light. Leaving out the active form misses the mechanism.
Explore the source
- MedlinePlus Genetics: can genes be turned on and off?US National Library of Medicine
A night-time flash can change a flowering signal
8B · Phytochrome and FloweringA study in tomato found that short interruptions of darkness and changes in red:far-red light altered flowering time and expression of flowering-related genes. The phytochrome B1 mutant changed…Specification 8.11Read & use the scienceClose article
Why this matters
A study in tomato found that short interruptions of darkness and changes in red:far-red light altered flowering time and expression of flowering-related genes. The phytochrome B1 mutant changed that response, giving evidence that a light receptor was involved. This is richer than saying “red light makes plants flower”: species, photoperiod and gene-regulatory context all matter. The 8.11 connection is that phytochrome can influence transcription, which later changes a developmental outcome. Researchers counted flowering and measured RNA; neither measurement alone is a photograph of phytochrome binding a promoter. The paper’s gene names are not required recall.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why does a mutant that loses a night-break response strengthen the case that phytochrome is involved?
Explore a possible response
Changing the receptor changes the outcome under the same light treatment. That links the receptor to the response, although other pathway components still need investigation.
Explore the source
- Phytochrome and tomato floweringPeer-reviewed research via NIH PubMed Central
The page is human genetics. The logic still fits a seedling.
8B · Phytochrome and TranscriptionMedlinePlus Genetics says signals activate transcription factors that bind regulatory DNA and change how much a gene is transcribed. That is the mechanism you should write for Pfr,…Specification 8.11Read & use the scienceClose article
Why this matters
MedlinePlus Genetics says signals activate transcription factors that bind regulatory DNA and change how much a gene is transcribed. That is the mechanism you should write for Pfr, auxin and gibberellin. The page does not name those plant molecules. Do not pretend it is a botany article. 8.11: phytochrome and the two hormones bring about responses by effects on transcription. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why is “the seed’s DNA changed to include amylase” the wrong description of germination?
Explore a possible response
The amylase gene is already in the DNA. Gibberellin changes its transcription. The sequence is not edited.
Explore the source
- MedlinePlus Genetics: can genes be turned on and off?US National Library of Medicine
Malting begins with a gene-expression decision
8B · Phytochrome and TranscriptionBarley researchers measured gibberellin-related transcripts and enzyme activity in different tissues of germinating grain. The study connects a crop process familiar to food production with 8.11: hormone signalling…Specification 8.11Read & use the scienceClose article
Why this matters
Barley researchers measured gibberellin-related transcripts and enzyme activity in different tissues of germinating grain. The study connects a crop process familiar to food production with 8.11: hormone signalling can promote transcription that leads to amylase production, allowing starch reserves to be mobilised for the young plant. The timing and tissue matter; a whole grain is not one uniform cell. This is also why the Unit 5 core practical on amylase in germinating cereals needs a control for germination stage. A high amylase reading alone does not identify the precise hormone concentration or gene-regulatory step that produced it.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.11 Phytochrome, auxin and gibberellin effects on plant responses and transcription.
Use the science
Why should an investigation of grain amylase compare seeds at a controlled stage of germination?
Explore a possible response
Gibberellin signalling and amylase production change as germination proceeds. Mixing stages could change enzyme activity independently of the variable the experiment aims to test.
Explore the source
- Gibberellin and gene activity in germinating barleyPeer-reviewed research via NIH PubMed Central
fMRI observes activation during a task
8B · Thinking BiggerNIBIB’s description is the boundary for this enrichment: fMRI is used to observe brain activation during cognitive tasks. It is a specialised MRI. It is not a mind-reading…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB’s description is the boundary for this enrichment: fMRI is used to observe brain activation during cognitive tasks. It is a specialised MRI. It is not a mind-reading claim, and the page does not mention guilt, personality, or school discipline. 8.15: use MRI, fMRI, PET and CT for structure or function, and stop where the measurement stops. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Which word in “functional” tells you a task should be named?
Explore a possible response
Functional. MRI alone is structure. fMRI needs a comparison of activity, which means the person was doing something, or the result is not an fMRI claim.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
Use the NIBIB sentence when a question exaggerates
8B · Exam PracticeNIBIB limits fMRI to observing activation during cognitive tasks, as a type of MRI. That is enough to reject a claim that a scanner reads motives. Plant answers…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB limits fMRI to observing activation during cognitive tasks, as a type of MRI. That is enough to reject a claim that a scanner reads motives. Plant answers are a different part of the same exam practice and do not come from that page. 8.10–8.16 mixed. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause. This is an extension to the lesson, not another fact to memorise.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Which scan from the specification uses a radioactive tracer rather than a magnet?
Explore a possible response
PET. MRI and fMRI use magnets. CT uses X-rays.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
The same idea made insulin
8C · Producing Recombinant DNAThe NHGRI glossary describes recombinant DNA technology as joining DNA segments, often from different species, and propagating them in bacterial or yeast cells. Its narration says the method…Specification 8.18Read & use the scienceClose article
Why this matters
The NHGRI glossary describes recombinant DNA technology as joining DNA segments, often from different species, and propagating them in bacterial or yeast cells. Its narration says the method has been used to make proteins for treating disease, including insulin and growth hormone. That is the link to the next lesson. This page does not give a dose or a brand protocol. 8.18 and 8.19: cut, join, and insert. Expression of the protein is what turns the method into a product.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.18 Restriction endonucleases and ligase in recombinant DNA.
Use the science
Why is “we grew bacteria on antibiotic agar” not yet evidence that human insulin was made?
Explore a possible response
The antibiotic only selects for the marker on the plasmid. Insulin is made only if the insulin gene is present, in a usable orientation, and is transcribed and translated.
Explore the source
- NHGRI: recombinant DNA technologyUS National Human Genome Research Institute
CRISPR is a different question from cut-and-join cloning
8C · Producing Recombinant DNANHGRI describes CRISPR as a technology adapted from bacterial systems to make targeted changes in living DNA. It appears often in headlines, but it is not the same…Specification 8.18Read & use the scienceClose article
Why this matters
NHGRI describes CRISPR as a technology adapted from bacterial systems to make targeted changes in living DNA. It appears often in headlines, but it is not the same operation as the 8.18 textbook method of cutting DNA with restriction endonucleases and joining fragments with ligase. Both involve enzymes and DNA specificity, yet their goals and steps differ. A news story about editing a gene in a cell should not be used as proof that a plasmid was assembled by the cut-and-join route. Students can compare the two methods without learning CRISPR’s molecular details for the Unit 5 exam.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.18 Restriction endonucleases and ligase in recombinant DNA.
Use the science
A headline says scientists edited a gene with CRISPR. Why does this not establish that they used DNA ligase to make a recombinant plasmid?
Explore a possible response
Editing DNA in a cell and assembling recombinant DNA are distinct workflows. The headline names one technology, not the specific restriction-and-ligation steps of a plasmid method.
Explore the source
- CRISPRUS National Human Genome Research Institute
Insulin was the proof the method could make a medicine
8C · Drugs from Genetically Modified OrganismsNHGRI’s history note on the first genetic engineering company says human insulin and growth hormone genes were isolated, and that by 1982 human insulin was marketed as the…Specification 8.17Read & use the scienceClose article
Why this matters
NHGRI’s history note on the first genetic engineering company says human insulin and growth hormone genes were isolated, and that by 1982 human insulin was marketed as the first recombinant DNA drug. The same note lists later proteins such as a clotting factor and a hepatitis B vaccine. Use that as history, not as a list you must memorise, and not as treatment advice. 8.17: microorganisms were the first factories. Plants and animals use the same idea of an inserted gene whose protein is the product.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.17 Drugs made using genetically modified organisms.
Use the science
Why is animal-pancreas insulin not an example of 8.17?
Explore a possible response
8.17 is production using a genetically modified organism. Extracting a protein from an unmodified pancreas does not involve an inserted gene.
Explore the source
- NHGRI: 1976 first genetic engineering companyUS National Human Genome Research Institute
Insulin was a manufacturing milestone
8C · Drugs from Genetically Modified OrganismsThe FDA’s history records the development of biosynthetic human insulin using recombinant DNA in bacteria and its first approval in 1982. The achievement was not just inserting a…Specification 8.17Read & use the scienceClose article
Why this matters
The FDA’s history records the development of biosynthetic human insulin using recombinant DNA in bacteria and its first approval in 1982. The achievement was not just inserting a gene: the organism had to make a useful protein that could be produced, purified and quality-checked as a medicine. That is the distinction between the method in 8.18–8.19 and the product in 8.17. A student should not assume that every genetically modified organism is released into the environment; drug-producing microorganisms can be grown in controlled facilities. This is a manufacturing and regulation story, not advice about an individual’s diabetes treatment.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.17 Drugs made using genetically modified organisms.
Use the science
Why is a bacterium containing a human gene not yet proof that a usable insulin medicine has been made?
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The inserted gene must be expressed to make the correct protein, and the product must be purified, tested and manufactured consistently before use as a medicine.
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- 100 years of insulinUS Food and Drug Administration
Turned on, then compared
8C · Microarrays and BioinformaticsThe NHGRI microarray fact sheet says microarrays can study the extent to which certain genes are turned on or off in cells and tissues, by isolating and measuring…Specification 8.20Read & use the scienceClose article
Why this matters
The NHGRI microarray fact sheet says microarrays can study the extent to which certain genes are turned on or off in cells and tissues, by isolating and measuring RNA. That is the expression pattern. Comparing the sequences themselves, at genome scale, is the computing in the bioinformatics glossary and is a separate page from the chip. 8.20 is the active-gene pattern. 8.21 is the computing that makes large sequence and expression data usable.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.20 Microarrays to identify active genes.
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Why can a sequence database not replace the mRNA extraction if the question is which genes are active today in this tissue?
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The database holds the sequence, which is present whether or not the gene is transcribed. Activity still needs evidence from RNA, which is what the microarray measures.
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- NHGRI: DNA microarray technologyUS National Human Genome Research Institute
A tumour profile measures RNA, not destiny
8C · Microarrays and BioinformaticsNHGRI explains that a microarray can use RNA-derived material to compare which genes are active in different samples. Researchers may use such expression profiles to investigate disease or…Specification 8.20Read & use the scienceClose article
Why this matters
NHGRI explains that a microarray can use RNA-derived material to compare which genes are active in different samples. Researchers may use such expression profiles to investigate disease or compare tissues. A fluorescent signal indicates hybridisation to a probe under the assay conditions; it does not show that the corresponding protein is present in the same quantity or that the gene caused a disease. Bioinformatics is needed to manage and compare the many measurements, but statistical patterns still require biological validation. This is a useful response to advertisements promising a diagnosis from one colourful gene-expression heat map.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.20 Microarrays to identify active genes.
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Why can a high microarray signal for one transcript not by itself prove that its protein is causing a tumour?
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The signal concerns RNA abundance, not protein amount or causation. Translation, protein breakdown and other variables can differ; experiments must test the proposed mechanism.
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- NHGRI: DNA microarray technologyUS National Human Genome Research Institute
Name the advantage, then name the issue
8C · Benefits and Risks of GMOsWHO says GM foods are developed because of a perceived advantage to the producer or the consumer, such as a lower price, durability or nutritional value, and that…Specification 8.22Read & use the scienceClose article
Why this matters
WHO says GM foods are developed because of a perceived advantage to the producer or the consumer, such as a lower price, durability or nutritional value, and that one objective is improved crop protection. The same page says three debated issues are allergenicity, gene transfer and outcrossing, and that environmental concerns include non-target organisms and escape of engineered genes into wild populations. Use both halves. Do not turn the page into a campaign. 8.22: a benefit is a trait. A risk is a mechanism, such as outcrossing or a non-target effect, not a slogan.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.22 Benefits and risks of genetically modified organisms.
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Why is “WHO says GM food is unsafe” an inaccurate use of that page?
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The page says foods on the international market have passed safety assessments and are not likely to present a risk to human health. It still lists issues that have to be assessed, including allergenicity, gene transfer and outcrossing.
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- WHO: food, genetically modifiedWorld Health Organization
A crop trait needs a case-by-case risk question
8C · Benefits and Risks of GMOsThe US National Academies’ evidence review treats genetically engineered crops as a set of technologies and traits, not one uniform product. A plant engineered to resist an insect…Specification 8.22Read & use the scienceClose article
Why this matters
The US National Academies’ evidence review treats genetically engineered crops as a set of technologies and traits, not one uniform product. A plant engineered to resist an insect and one altered for a nutritional property have different potential benefits and different questions for environmental assessment. Gene flow to compatible relatives, changes in pesticide use and effects on non-target organisms need evidence in the relevant setting. The 8.22 skill is to weigh a specified benefit against a specified risk, rather than declare all GMOs safe or dangerous from a label. Published assessments are evidence, not a substitute for local monitoring.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.22 Benefits and risks of genetically modified organisms.
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Why would evidence about one insect-resistant crop be insufficient to assess a different crop engineered for nutrition?
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The inserted trait, receiving species, relatives, farming system and exposure pathways differ. Benefits and risks must be tested for the actual crop and setting.
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- Genetically engineered crops: experiences and prospectsUS National Academies of Sciences, Engineering, and Medicine
Computers hold the sequences
8C · Thinking BiggerNHGRI describes bioinformatics as using computers to collect, store, analyse and share biological data such as DNA and amino-acid sequences. That is the right size of claim for…Specification 8.21Read & use the scienceClose article
Why this matters
NHGRI describes bioinformatics as using computers to collect, store, analyse and share biological data such as DNA and amino-acid sequences. That is the right size of claim for an alignment. A match in a database is a reason to look again in the laboratory. It is not a finished medicine, and it says nothing about outcrossing if someone later puts the gene into a crop. 8.20–8.22: expression, computing, and the risks of the organism you choose to use.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.21 Bioinformatics and biological data.
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Why is a database match not evidence about pollen?
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An alignment compares sequences. Pollen and outcrossing are properties of a released plant. The database does not describe that field.
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- NHGRI: bioinformaticsUS National Human Genome Research Institute
Method, product, pattern, judgement
8C · Exam PracticeNHGRI describes recombinant DNA technology, including its use to make proteins such as insulin, and describes microarrays as a way to see genes turned on or off. WHO…Specification 8.18Read & use the scienceClose article
Why this matters
NHGRI describes recombinant DNA technology, including its use to make proteins such as insulin, and describes microarrays as a way to see genes turned on or off. WHO separates a crop-protection benefit from issues such as allergenicity, gene transfer and outcrossing. An exam answer can use that shape: how the DNA was built, what the product is, what a spot means, and one risk with a mechanism. 8.17–8.22 together. A manufactured product or array signal establishes an outcome, but cannot by itself reveal every cloning step or settle every risk.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.18 Restriction endonucleases and ligase in recombinant DNA.
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Which of a bright microarray spot and a sealed recombinant plasmid shows that a gene was already active in a tissue?
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The bright spot, because it reports mRNA from that tissue. A recombinant plasmid shows that someone joined DNA. It says nothing about what the original tissue was transcribing.
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- NHGRI: recombinant DNA technologyUS National Human Genome Research Institute