Unit 1 biology.
Out in the world.
From artificial arteries to Jurassic Park. Follow the science into real jobs, research and everyday claims, then put your understanding to work.
Follow your curiosity
Choose a theme or explore the whole collection. Open a card, try its question, then compare your reasoning with a possible response. Nothing is submitted or saved.
72 articles across Unit 1. An article can belong to more than one theme.
Water carries a chemical story
1A · The Chemistry of LifeEnvironmental scientists investigate substances carried in water. The same solvent behaviour that makes biological transport possible allows water to carry dissolved minerals through the environment. Imagine comparing water…Specification 1.1Read & use the scienceClose article
Why this matters
Environmental scientists investigate substances carried in water. The same solvent behaviour that makes biological transport possible allows water to carry dissolved minerals through the environment. Imagine comparing water upstream and downstream of a discharge: a transparent sample can still carry dissolved ions and polar molecules. Water’s partial charges help explain why these substances travel with it, but cannot identify which substances are present. The investigation therefore needs measurements, comparable sampling conditions and a sensible reference site. This is the useful connection to biological transport: a solvent makes movement possible without making the transported substance visible, harmless or chemically identified.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.1 understand the importance of water as a solvent in transport, including its dipole nature
Use the science
A clear river sample looks clean. Does its appearance show that it contains no dissolved substances?
Explore a possible response
No. Dissolved ions and many dissolved molecules are invisible. Appearance alone cannot establish composition; an appropriate chemical analysis is needed.
Explore the source
- US Geological Survey: water as a solventUS Geological Survey
Why water cannot wash away an oil spill
1A · The Chemistry of LifeAn oil-spill scientist has to predict where pollution will travel and which clean-up method might help. Water is a good solvent for many ionic and polar substances, but…Specification 1.1Read & use the scienceClose article
Why this matters
An oil-spill scientist has to predict where pollution will travel and which clean-up method might help. Water is a good solvent for many ionic and polar substances, but that does not make it a solvent for everything. Much of an oil mixture behaves differently from dissolved salts: it can form a separate phase rather than a uniform solution. Responders must also consider currents, weather and damage caused by the clean-up itself. NOAA describes cases where aggressive washing harmed shorelines. Molecular properties therefore inform an environmental decision, but cannot settle that decision without ecological evidence.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.1 understand the importance of water as a solvent in transport, including its dipole nature
Use the science
Why could filtering visible oil droplets from seawater fail to remove every dissolved contaminant? Use polarity and the distinction between a mixture and a solution.
Explore a possible response
Droplets are a separate phase and may be trapped; dissolved molecules pass with the water. Different components have different solubilities, so visual clarity is not evidence of chemical purity.
Explore the sources
- Oil spillsNOAA
- Oil, petroleum, N.O.S.NOAA CAMEO Chemicals
The chemistry behind lactose-free milk
1A · Carbohydrates 1: Monosaccharides and DisaccharidesLactase breaks down lactose. Low lactase activity can lead to incomplete lactose digestion and, in some people, symptoms of lactose intolerance. This gives food scientists a practical reason…Specification 1.4Read & use the scienceClose article
Why this matters
Lactase breaks down lactose. Low lactase activity can lead to incomplete lactose digestion and, in some people, symptoms of lactose intolerance. This gives food scientists a practical reason to investigate sugar hydrolysis. For a food scientist, changing a disaccharide into two monosaccharides changes the product without removing its carbohydrate. Water is used to hydrolyse the glycosidic bond; glucose and galactose remain. A label saying lactose-free therefore answers a different question from a label about total sugars. Product testing must distinguish the molecules present, rather than assuming a successful reaction has made them disappear. The NIDDK explanation provides the digestive context; applying that chemistry to a milk label is the biological reasoning.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
If lactose is hydrolysed in milk, does that mean all the sugar has been removed?
Explore a possible response
No. Hydrolysis converts lactose into glucose and galactose. Changing the identity of a sugar is different from removing sugar.
Explore the sources
Go to the lesson: Carbohydrates 1: Monosaccharides and Disaccharides →Can a blue test tube prove a drink has no sugar?
1A · Carbohydrates 1: Monosaccharides and DisaccharidesA food analyst and a drinks advertisement may use the word sugar in different ways. The FDA distinguishes total sugars from sugars added during manufacture: a drink can…Specification 1.2(i) · 1.3 · 1.4Read & use the scienceClose article
Why this matters
A food analyst and a drinks advertisement may use the word sugar in different ways. The FDA distinguishes total sugars from sugars added during manufacture: a drink can contain naturally occurring sugars without having sugar added. Your Benedict’s test asks another question, about reducing sugars. It is not a universal detector for every carbohydrate, nor can it tell whether a glucose molecule came from fruit or a factory. Comparing a chemical test with a label requires checking exactly what each measures, using appropriate standards and allowing for the colour of the drink itself.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.3 CORE PRACTICAL 1 Use a semi-quantitative method with Benedict’s reagent to estimate the concentrations of reducing sugars and with iodine solution to estimate the concentrations of starch, using colour standards.
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
A sucrose-containing drink gives a negative Benedict’s test before hydrolysis. Explain why the claim “laboratory-proven sugar-free” does not follow.
Explore a possible response
Sucrose is non-reducing under the test conditions. Hydrolysis produces reducing monosaccharides. A negative reducing-sugar result cannot establish absence of all sugars; appropriate controls and sensitivity also matter.
Explore the source
Go to the lesson: Carbohydrates 1: Monosaccharides and Disaccharides →Could starch become packaging?
1A · Carbohydrates 2: PolysaccharidesResearchers have modified starch to make flexible plastic materials. A University of Leicester study investigated adding a salt to change interactions between starch chains. This is a new…Specification 1.2(i) · 1.2(ii)Read & use the scienceClose article
Why this matters
Researchers have modified starch to make flexible plastic materials. A University of Leicester study investigated adding a salt to change interactions between starch chains. This is a new use for a familiar biological polymer. An energy-storage molecule becomes a material because many polymer chains can interact. Changing those interactions can change flexibility without turning every chain into glucose. This particular research is evidence for a material-making method, not proof that every starch product is environmentally preferable. A materials scientist would also need to measure strength, water sensitivity and what happens after disposal. Knowing the monomers is a starting point; judging a replacement for packaging requires testing the properties of the whole material.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.2(ii) be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy
Use the science
A starch-based film becomes more flexible after treatment, but no extra glucose is detected. Why does this not necessarily show that glycosidic bonds were hydrolysed, and what further evidence would be needed to judge its environmental value?
Explore a possible response
Flexibility can change when interactions between intact polymer chains change; it need not involve hydrolysis into glucose. Testing chain length or hydrolysis products would help distinguish mechanisms. Environmental evaluation also needs evidence about manufacture, useful lifetime and disposal, rather than assuming a starch starting material guarantees a better outcome.
Explore the source
- Abbott and colleagues (2012): salt-modified starch plasticsGreen Chemistry, Royal Society of Chemistry (2012)
What are endurance athletes actually storing?
1A · Carbohydrates 2: PolysaccharidesCarbohydrate loading in endurance sport is about changing the availability of stored fuel, not filling muscles with a pool of free glucose. Research on exercise performance has investigated…Specification 1.2(i) · 1.2(ii) · 1.4Read & use the scienceClose article
Why this matters
Carbohydrate loading in endurance sport is about changing the availability of stored fuel, not filling muscles with a pool of free glucose. Research on exercise performance has investigated muscle glycogen and how its availability relates to prolonged activity. Glycogen is a branched polymer: storing many glucose units in large molecules reduces the number of freely dissolved particles compared with storing the same units separately. Its structure also provides many ends from which units can be mobilised. This explains why molecular architecture matters to a sporting practice, while leaving training, event length and individual responses as additional variables.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.2(ii) be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
Why would storing an equivalent number of glucose units as free glucose create a different osmotic problem from storing them as glycogen?
Explore a possible response
Many separate glucose molecules exert a larger effect on water potential than far fewer polymer molecules; more water would tend to enter. This is a qualitative comparison, not a claim that glycogen stores contain no water.
Explore the source
- What Is the Evidence That Dietary Macronutrient Composition Influences Exercise Performance? A Narrative ReviewNutrients / PubMed
What does an oil label really tell you?
1A · LipidsFood chemists can compare unsaturation through reactions at carbon–carbon double bonds. This connects a label such as “unsaturated fat” to a measurable molecular feature, rather than simply the…Specification 1.5(ii)Read & use the scienceClose article
Why this matters
Food chemists can compare unsaturation through reactions at carbon–carbon double bonds. This connects a label such as “unsaturated fat” to a measurable molecular feature, rather than simply the appearance of the food. A food label compresses molecular information into categories such as saturated and unsaturated. A double bond changes a fatty-acid chain, but the nutritional implications depend on the mixture, the amount consumed and what food replaces what. Chemists can describe the bonding precisely while researchers still investigate health outcomes. This distinction helps when an advert turns one structural feature into a promise of health: identifying a molecule is not the same experiment as measuring the effects of eating it.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.5(ii) know the differences between saturated and unsaturated lipids
Use the science
A social-media post calls every liquid oil “healthy” because it is unsaturated. What can the molecular classification establish, and what can it not establish?
Explore a possible response
It can describe the presence of C=C bonds. On its own it cannot establish the overall health effect of a food or diet; amount consumed, other ingredients and evidence about outcomes also matter.
Explore the source
- Royal Society of Chemistry: measuring unsaturationRoyal Society of Chemistry
From used cooking oil to fuel
1A · LipidsUsed cooking oil can become a feedstock for biodiesel, but pouring it straight into an engine is not the same process. Triglycerides are chemically converted into smaller fatty-acid…Specification 1.5(i)Read & use the scienceClose article
Why this matters
Used cooking oil can become a feedstock for biodiesel, but pouring it straight into an engine is not the same process. Triglycerides are chemically converted into smaller fatty-acid esters and glycerol in a reaction called transesterification. You already know that triglycerides contain ester bonds linking fatty acids to glycerol; the industrial reaction rearranges those connections using an alcohol. It changes properties such as viscosity, which matters when a fuel must flow and spray reliably. Calling a fuel biological also does not establish its full environmental footprint: the feedstock, processing energy and competing land uses still matter.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.5(i) know how a triglyceride is synthesised by the formation of ester bonds during condensation reactions between glycerol and three fatty acids
Use the science
Why is producing biodiesel a chemical change rather than simply melting a fat? Refer to triglyceride structure.
Explore a possible response
Melting changes physical state without changing covalent bonding. Transesterification changes ester connections and produces different molecules, including glycerol and fatty-acid esters.
Explore the source
- Biodiesel Production and DistributionUS Department of Energy, Alternative Fuels Data Center
A small sequence change, a large consequence
1A · ProteinsSickle cell disease illustrates how a change in haemoglobin can affect red blood cells. It connects molecular structure with cell behaviour and shows why researchers study the consequences…Specification 2.6(iii) · 2.6(iv)Read & use the scienceClose article
Why this matters
Sickle cell disease illustrates how a change in haemoglobin can affect red blood cells. It connects molecular structure with cell behaviour and shows why researchers study the consequences of changes in protein sequences. This example connects protein chemistry with a question researchers can investigate: how can one changed residue influence interactions between protein molecules? The surrounding amino-acid sequence, folding and oxygen conditions matter, so the change should not be described as every protein simply unfolding. At this stage, use it to connect primary structure with properties and function. Inheritance patterns and the clinical management of sickle cell disease are further topics, rather than extra facts required for the chemistry lesson.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.6(iii) understand the significance of a protein’s primary structure in determining its secondary structure, three-dimensional structure and properties (globular and fibrous proteins and the types of bonds involved in its three-dimensional structure)
- 2.6(iv) know the molecular structure of a globular protein and a fibrous protein and understand how their structures relate to their functions (including haemoglobin and collagen)
Use the science
Why would seeing a changed amino acid sequence alone be insufficient to predict the full effect on an organism?
Explore a possible response
The effect depends on the residue’s role, folding, interactions with other molecules and the cellular context. Measurements of protein behaviour and cells are needed to connect a sequence change to an organism-level effect.
Explore the source
- YourGenome: sickle cell anaemiaYourGenome
Can AI predict a protein’s shape?
1A · ProteinsThe 2024 Chemistry Nobel recognised protein structure prediction and computational protein design. These advances turn the connection between an amino-acid sequence and a three-dimensional molecule into a research…Specification 2.6(iii) · 2.6(iv)Read & use the scienceClose article
Why this matters
The 2024 Chemistry Nobel recognised protein structure prediction and computational protein design. These advances turn the connection between an amino-acid sequence and a three-dimensional molecule into a research tool. A predicted structure can suggest where another molecule might bind, or help researchers decide which experiment to do next. It is still a prediction: proteins move, interact and work in particular chemical environments. A convincing picture alone cannot demonstrate that a protein catalyses a reaction, survives a temperature change or behaves normally inside a cell. Structural prediction helps ask sharper biological questions; experimental measurements establish what the molecule actually does.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.6(iii) understand the significance of a protein’s primary structure in determining its secondary structure, three-dimensional structure and properties (globular and fibrous proteins and the types of bonds involved in its three-dimensional structure)
- 2.6(iv) know the molecular structure of a globular protein and a fibrous protein and understand how their structures relate to their functions (including haemoglobin and collagen)
Use the science
Two variants are predicted to have similar overall shapes. Why might their biological activities still differ, and what experiment would you propose?
Explore a possible response
A small change at a binding site, charge or flexibility can alter interactions without changing the overall fold. Compare a relevant measured activity under controlled conditions.
Explore the source
- The Nobel Prize in Chemistry 2024: Press releaseRoyal Swedish Academy of Sciences / Nobel Prize
A name is not a structure
1A · Thinking Bigger: TrehaloseFlyBase’s chemical entry identifies trehalose by its structure and links to chemical databases. Researchers need precise chemical identity when comparing experiments. For a food chemist, a familiar-sounding name…Specification 1.2(i) · 1.4Read & use the scienceClose article
Why this matters
FlyBase’s chemical entry identifies trehalose by its structure and links to chemical databases. Researchers need precise chemical identity when comparing experiments. For a food chemist, a familiar-sounding name is not enough to predict digestion. Two sugars can contain the same kinds of atom yet arrange their bonds differently. Whether a particular enzyme hydrolyses them depends on that arrangement and on its active site. Trehalose offers a useful unfamiliar case: apply the supplied structural evidence instead of guessing from an ending such as “-ose”. This is also why a claim about one sugar cannot automatically be transferred to every other sugar.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.2(i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin)
- 1.4 know how monosaccharides (glucose, fructose and galactose) join together to form disaccharides (maltose, sucrose and lactose) and polysaccharides (glycogen, amylose and amylopectin) through condensation reactions forming glycosidic bonds, and how these can be split through hydrolysis reactions
Use the science
Why is “a glucose-based sugar” too vague for a reproducible experiment?
Explore a possible response
It does not identify whether the sample is glucose, a particular disaccharide or a polymer, nor the linkages or concentration.
Explore the source
- FlyBase: trehaloseFlyBase
Keeping an organ supplied outside the body
1B · The Principles of CirculationMachine perfusion systems circulate oxygenated blood or nutrient-rich fluid through donated organs. They apply the same transport principles as a circulation while an organ is outside the body.…Specification 1.6Read & use the scienceClose article
Why this matters
Machine perfusion systems circulate oxygenated blood or nutrient-rich fluid through donated organs. They apply the same transport principles as a circulation while an organ is outside the body. Perfusion means supplying an organ with a flowing fluid. Outside the body, a system must provide suitable conditions as well as move that fluid: oxygen delivery and waste removal still matter. A report about extending a preservation window describes a particular method and setting, not a guarantee for every donated organ. The transport lesson explains why circulation is part of the problem. Researchers must then test whether the organ remains suitable for transplantation, rather than judging success from visible flow alone.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
Use the science
Why might circulating oxygenated fluid through an organ be more effective than simply surrounding it with that fluid?
Explore a possible response
Flow through its vessels brings fluid close to internal cells, shortening diffusion distances and helping maintain gradients. Surrounding a large organ leaves its deepest cells far from the external supply.
Explore the source
- NHS Blood and Transplant: machine preservation programmeNHS Blood and Transplant
The scientist who runs a temporary circulation
1B · The Principles of CirculationDuring some heart operations, a clinical perfusionist operates equipment that temporarily supports circulation and gas exchange. This professional monitors the system rather than merely switching on a pump.…Specification 1.6 · 1.8Read & use the scienceClose article
Why this matters
During some heart operations, a clinical perfusionist operates equipment that temporarily supports circulation and gas exchange. This professional monitors the system rather than merely switching on a pump. Blood must reach tissues, acquire oxygen and release carbon dioxide while the surgical team works. Your distinction between mass transport and diffusion explains the division of labour: the machine moves blood over long distances, while exchange still depends on gradients across a thin barrier. The career combines physiology, measurements and rapid communication with other specialists. It also shows why a functioning oxygenator is not enough if blood is not reaching the organs.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
Use the science
The oxygenator works normally but the rate of blood flow falls substantially. Explain why tissue oxygen supply can still fall.
Explore a possible response
Oxygen content per volume is not the same as delivery per minute. Lower flow supplies fewer oxygenated red cells and may fail to maintain the tissue diffusion gradient.
Explore the source
- PerfusionRoyal Brompton & Harefield hospitals, NHS
Why donated blood is separated
1B · The Roles of the BloodNHS Blood and Transplant manufacturing teams separate donations into components including red cells, platelets and plasma. Understanding what each component does is part of making blood products useful…Specification 1.9(i)Read & use the scienceClose article
Why this matters
NHS Blood and Transplant manufacturing teams separate donations into components including red cells, platelets and plasma. Understanding what each component does is part of making blood products useful for different clinical needs. Separation allows a clinical team to match a component to a particular need. Red cells contribute oxygen-carrying capacity; platelets contribute to clot formation; plasma contains dissolved substances and proteins. Those functions are related but not interchangeable. A laboratory scientist must therefore identify and handle the appropriate component rather than treat all red fluid as equivalent. The Unit 1 link is structure and function: a transfusion decision depends on which biological role needs support, alongside compatibility and other clinical checks.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.9(i) understand the role of haemoglobin in the transport of oxygen and carbon dioxide
Use the science
Why would a bag of plasma not have the same oxygen-carrying capacity as a red-cell preparation of equal volume?
Explore a possible response
Plasma lacks the large amount of haemoglobin inside red cells. Although a small amount of oxygen can dissolve in fluid, haemoglobin provides much greater oxygen-carrying capacity.
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Go to the lesson: The Roles of the Blood →What does an oxygen reading really measure?
1B · The Roles of the BloodA pulse oximeter estimates the proportion of haemoglobin carrying oxygen using light. That useful number is not a direct measurement of how much oxygen reaches every tissue. Haemoglobin…Specification 1.9(i) · 1.16Read & use the scienceClose article
Why this matters
A pulse oximeter estimates the proportion of haemoglobin carrying oxygen using light. That useful number is not a direct measurement of how much oxygen reaches every tissue. Haemoglobin concentration and blood flow also influence delivery. Research has additionally found differences in measurement performance across skin pigmentation, prompting the FDA’s 2025 proposals for improved validation studies. This connects the biology of oxygen transport with the design of fair medical technologies. A device should be tested in people representative of those who will use it, and an apparently precise display should not hide uncertainty about the measurement.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.9(i) understand the role of haemoglobin in the transport of oxygen and carbon dioxide
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Two samples have the same oxygen saturation but different haemoglobin concentrations. Would equal volumes necessarily carry the same amount of oxygen? Explain.
Explore a possible response
No. The same fraction of a smaller amount of haemoglobin carries less bound oxygen; saturation alone does not specify oxygen content.
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Go to the lesson: The Roles of the Blood →When a one-way system leaks
1B · Circulation in the Blood VesselsWeak or damaged vein walls and valves can allow blood to move in the wrong direction, contributing to varicose veins. This is a real-world example of how a…Specification 1.7Read & use the scienceClose article
Why this matters
Weak or damaged vein walls and valves can allow blood to move in the wrong direction, contributing to varicose veins. This is a real-world example of how a small structural change can affect circulation. Venous return often works against gravity, assisted by surrounding muscle contractions and valves that limit backward flow. If valves fail to close effectively, pressure and pooling can change even though the vessel remains open. That is a different mechanical problem from a narrowed artery. Comparing the two avoids treating all circulation disorders as blocked tubes. Vessel-wall properties, pressure differences and one-way flow jointly explain the system; the appearance of a vein alone does not reveal every cause of a symptom.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.7 understand how the structures of blood vessels (capillaries, arteries and veins) relate to their functions
Use the science
Why is valve function particularly relevant to blood returning from the legs of a standing person?
Explore a possible response
Blood must return upwards against gravity at relatively low pressure. Valves limit downward backflow between muscle contractions, helping maintain net movement towards the heart.
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Go to the lesson: Circulation in the Blood Vessels →Can scientists manufacture a replacement artery?
1B · Circulation in the Blood VesselsIn 2024, the FDA approved a tissue-engineered vessel for a specific emergency use: repairing certain severe limb-artery injuries when a suitable vein graft is not feasible. The product…Specification 1.7 · 2.6(iv)Read & use the scienceClose article
Why this matters
In 2024, the FDA approved a tissue-engineered vessel for a specific emergency use: repairing certain severe limb-artery injuries when a suitable vein graft is not feasible. The product contains extracellular matrix proteins made using human cells; acellular means the implanted material does not contain those manufacturing cells. It is therefore more than an inert plastic tube, but it is not an entire newly grown circulatory system. The structure–function problem is familiar: the conduit must allow blood flow and withstand arterial conditions. Researchers and regulators also need evidence about complications and long-term performance, not just whether a tube can be manufactured.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.7 understand how the structures of blood vessels (capillaries, arteries and veins) relate to their functions
- 2.6(iv) know the molecular structure of a globular protein and a fibrous protein and understand how their structures relate to their functions (including haemoglobin and collagen)
Use the science
Why would the very thin wall useful in a capillary be an unsuitable design target for a replacement artery?
Explore a possible response
Capillaries favour short diffusion distances at lower pressure; arteries must withstand higher pulsatile pressure. The mechanical requirements differ.
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Go to the lesson: Circulation in the Blood Vessels →Seeing flow rather than guessing from a heartbeat
1B · The Mammalian HeartDoppler ultrasound can show blood flow through heart chambers and valves. This helps clinicians investigate valve function, linking images and flow information to the pressure-and-valve model you have…Specification 1.8Read & use the scienceClose article
Why this matters
Doppler ultrasound can show blood flow through heart chambers and valves. This helps clinicians investigate valve function, linking images and flow information to the pressure-and-valve model you have learned. Doppler measurements use changes in reflected ultrasound to investigate movement. In cardiac assessment, a moving structure or a detectable heartbeat does not by itself establish that blood passes through valves normally. Flow measurements add evidence about direction and speed, which must be interpreted with the anatomy and the rest of the examination. Students do not need the ultrasound physics here. The useful biological question is whether pressure changes, valve action and blood movement agree with the proposed explanation.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
Use the science
A drama shows a character checking a pulse and declaring every heart valve healthy. Why is that conclusion too strong?
Explore a possible response
A pulse provides evidence of pulsatile arterial flow, but does not directly show whether each valve closes completely or whether some blood flows backwards. Assessing valve function requires more specific evidence.
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Go to the lesson: The Mammalian Heart →A replacement valve is a biological trade-off
1B · The Mammalian HeartA replacement heart valve must open and close under changing pressure, restoring directional flow. Choosing a valve also brings a longer-term trade-off. NHS information distinguishes durable mechanical valves…Specification 1.8 · 1.11 · 1.20Read & use the scienceClose article
Why this matters
A replacement heart valve must open and close under changing pressure, restoring directional flow. Choosing a valve also brings a longer-term trade-off. NHS information distinguishes durable mechanical valves from tissue valves; mechanical valves carry a clotting risk that requires anticoagulant treatment, while tissue valves may eventually need replacement. A cardiac team therefore combines the mechanics you study with evidence about blood clotting, treatment risks and a patient’s circumstances. The most durable material is not automatically the best choice for every person. This is a useful example of a device solving one biological problem while creating another that needs management.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
- 1.11 understand the blood clotting process (thromboplastin release, conversion of prothrombin to thrombin and fibrinogen to fibrin) and its role in cardiovascular disease (CVD)
- 1.20 know the benefits and risks of treatments for cardiovascular disease (CVD) (antihypertensives, statins, anticoagulants and platelet inhibitors)
Use the science
Explain why a valve could prevent backflow successfully but still require anticoagulant treatment.
Explore a possible response
Directional flow and clot formation are different properties. Contact with a mechanical valve can increase clot risk even when its opening and closing function is effective.
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Go to the lesson: The Mammalian Heart →More than “clogged pipes”
1B · AtherosclerosisResearch and clinical explanations of atherosclerosis include inflammation and cells within the artery wall. The familiar “clogged pipe” image captures narrowing, but leaves out the living tissue and…Specification 1.10 · 1.11Read & use the scienceClose article
Why this matters
Research and clinical explanations of atherosclerosis include inflammation and cells within the artery wall. The familiar “clogged pipe” image captures narrowing, but leaves out the living tissue and biological processes that create a plaque. A plaque is a biological change in an artery wall, involving lipids and cells, rather than loose fat poured into a pipe. A disrupted plaque can promote formation of a thrombus that suddenly restricts supply. The distinction matters because a gradual narrowing and an acute clot need not produce the same timing of symptoms. Connecting wall changes, clotting and oxygen delivery gives a more useful explanation than a cartoon of greasy plumbing, even when that cartoon dominates popular descriptions.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.10 understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure)
- 1.11 understand the blood clotting process (thromboplastin release, conversion of prothrombin to thrombin and fibrinogen to fibrin) and its role in cardiovascular disease (CVD)
Use the science
A video shows cooking fat poured into a drain as its complete explanation of atherosclerosis. Identify one useful feature of the analogy and two important limitations.
Explore a possible response
It illustrates that narrowing can restrict flow. It does not represent inflammatory cells and lipid processing within a living artery wall, or plaque rupture triggering a platelet-and-fibrin thrombus. It also risks implying that dietary fat simply deposits directly as a lump.
Explore the source
Go to the lesson: Atherosclerosis →Plastic in an artery: discovery or proof?
1B · AtherosclerosisA 2024 observational study analysed plaques removed from people undergoing carotid-artery surgery. Patients whose plaques contained detected plastics had a higher subsequent rate of a combined outcome involving…Specification 1.10 · 1.15 · 1.16Read & use the scienceClose article
Why this matters
A 2024 observational study analysed plaques removed from people undergoing carotid-artery surgery. Patients whose plaques contained detected plastics had a higher subsequent rate of a combined outcome involving heart attack, stroke or death. That finding connects an environmental exposure with the living, inflammatory tissue of an atheroma. It does not demonstrate that the plastics caused those events: the groups may differ in other ways, and these were selected patients with existing artery disease. The important research question is how detection, biological mechanism and clinical outcome fit together. Each requires evidence; none is automatically established by the others.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.10 understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure)
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Why would finding plastic and inflammatory markers in the same plaque still be insufficient to establish that plastic caused the inflammation?
Explore a possible response
Co-occurrence does not establish timing or exclude confounding and preferential accumulation in damaged tissue. Controlled mechanistic evidence and additional studies would strengthen inference.
Explore the source
- Microplastics and Nanoplastics in Atheromas and Cardiovascular EventsMarfella et al., New England Journal of Medicine (2024)
When “same category” does not mean “same risk”
1C · Risk, Correlation and CauseA headline can put processed meat and tobacco in the same carcinogenicity category and leave readers with a misleading comparison. IARC’s categories describe the strength of evidence that…Specification 1.15 · 1.17Read & use the scienceClose article
Why this matters
A headline can put processed meat and tobacco in the same carcinogenicity category and leave readers with a misleading comparison. IARC’s categories describe the strength of evidence that an exposure can cause cancer, not an equal size of risk at ordinary exposures. The distinction transfers directly to the health-risk reasoning in Unit 1: identify the outcome, exposure, baseline risk and time period before comparing claims. Biological mechanisms can help make an explanation plausible, but a category label is not a probability. Scientific communication needs to preserve that difference even when a dramatic headline would attract more attention.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.17 understand why people’s perception of risks are often different from the actual risks, including underestimating and overestimating the risks due to diet and other lifestyle factors in the development of heart disease
Use the science
What quantitative information would you need before comparing the risk from two exposures placed in the same evidence category?
Explore a possible response
Absolute baseline and exposed risks, defined doses and durations, comparable outcomes, population characteristics and uncertainty. Evidence strength alone gives none of these effect sizes.
Explore the source
- Q&A on the carcinogenicity of the consumption of red meat and processed meatInternational Agency for Research on Cancer, WHO (2015)
Following families across generations
1C · Investigating the Causes of CVDsThe Framingham Heart Study follows cardiovascular health over time and across generations. Its long-term design illustrates how researchers investigate factors that precede disease. Following participants over time can…Specification 1.16Read & use the scienceClose article
Why this matters
The Framingham Heart Study follows cardiovascular health over time and across generations. Its long-term design illustrates how researchers investigate factors that precede disease. Following participants over time can establish that a measured exposure preceded an outcome, an advantage over a one-off snapshot. Repeated measurements can also reveal that risk factors change. Yet participants are not randomly assigned to their lives: smoking, diet, income and other influences can overlap. An epidemiologist uses careful comparisons and adjustment, while acknowledging remaining uncertainty. A long-running study is valuable evidence for cardiovascular risk, but its duration alone cannot turn every association into a proven causal mechanism.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Why could measuring an exposure repeatedly be better than measuring it only at enrolment?
Explore a possible response
Diet, activity or smoking can change. Repeated measurements reduce misclassification and provide a more accurate picture of exposure over time.
Explore the source
Go to the lesson: Investigating the Causes of CVDs →Why a warning needs more than a slogan
1C · Risk Factors for Cardiovascular DiseaseCDC identifies smoking as a cause of cardiovascular disease and describes effects on blood vessels and clotting. Public-health communication can connect this evidence to mechanisms rather than relying…Specification 1.12Read & use the scienceClose article
Why this matters
CDC identifies smoking as a cause of cardiovascular disease and describes effects on blood vessels and clotting. Public-health communication can connect this evidence to mechanisms rather than relying only on frightening images. For example, explaining how carbon monoxide reduces oxygen-carrying capacity gives a warning a biological chain rather than only an alarming image. Nicotine, carbon monoxide and other smoke components have different effects, so the message should identify the relevant substance. A public-health scientist also needs evidence about whether the message changes behaviour and who it reaches. A scientifically accurate mechanism and an effective intervention are related questions, but success at one does not automatically demonstrate success at the other.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.12 know how factors such as genetics, diet, age, gender, high blood pressure, smoking and inactivity increase the risk of cardiovascular disease (CVD)
Use the science
A warning says carbon monoxide makes the heart work harder. Explain a biological chain connecting carbon monoxide exposure with oxygen supply, and why that mechanism alone does not prove the warning changes behaviour.
Explore a possible response
Carbon monoxide binds strongly to haemoglobin, reducing its oxygen-carrying capacity. Less oxygen can be delivered for a given blood flow, potentially increasing the demand on circulation. To show the message changes behaviour, researchers must measure behaviour using a suitable comparison; knowing the mechanism is not evidence of that communication outcome.
Explore the source
Go to the lesson: Risk Factors for Cardiovascular Disease →A heatwave is also a cardiovascular event
1C · Risk Factors for Cardiovascular DiseaseHot weather can place extra demands on the cardiovascular system. The CDC describes how heat stress, dehydration and changes in clotting risk can contribute to cardiovascular problems, particularly…Specification 1.6 · 1.12 · 1.15Read & use the scienceClose article
Why this matters
Hot weather can place extra demands on the cardiovascular system. The CDC describes how heat stress, dehydration and changes in clotting risk can contribute to cardiovascular problems, particularly in people with existing disease. This expands the familiar list of lifestyle and inherited risks to include environmental conditions. The transport system must keep supplying tissues while the body responds to heat, and people differ in their capacity to cope. Studying hospital admissions during a heatwave also requires care: age, existing illness, air pollution and access to cooling can all affect the observed pattern. Exposure is not distributed equally across a population.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- 1.12 know how factors such as genetics, diet, age, gender, high blood pressure, smoking and inactivity increase the risk of cardiovascular disease (CVD)
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
Use the science
Why would a higher death count on hot days alone be insufficient to calculate how much heat increases an individual’s cardiovascular risk?
Explore a possible response
Counts need denominators and comparable populations, while pollution, age, illness and other factors may confound the association. Individual baseline risk varies.
Explore the source
Go to the lesson: Risk Factors for Cardiovascular Disease →Can a single number describe health?
1C · Diet and Cardiovascular HealthCDC describes BMI as a screening measure that needs interpretation alongside other information. This is useful when evaluating apps and social-media posts that turn a single number into…Specification 1.19Read & use the scienceClose article
Why this matters
CDC describes BMI as a screening measure that needs interpretation alongside other information. This is useful when evaluating apps and social-media posts that turn a single number into a complete health judgement. BMI combines mass and height, but does not directly measure fat distribution, muscle mass or cardiovascular function. For children and teenagers, interpretation also depends on age and sex; adult thresholds should not simply be applied to an A-level class. In population research, a simple measure may reveal useful patterns while giving incomplete information about an individual. The lesson is to identify what a measurement captures and what it misses, without turning a classroom calculation into a personal health judgement.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.19 understand how people use scientific knowledge about the effect of diet, including obesity indicators, such as body mass index and waist-to-hip ratio, exercise and smoking to reduce their risk of coronary heart disease
Use the science
What is missing from a claim that two people with equal BMI must be equally healthy?
Explore a possible response
Information about body composition, fat distribution, cardiovascular measurements and other risk factors. Equal BMI is not equal health.
Explore the source
Go to the lesson: Diet and Cardiovascular Health →High cholesterol can run in a family
1C · Diet and Cardiovascular HealthFamilial hypercholesterolaemia is an inherited condition in which the body’s handling of cholesterol leads to high LDL cholesterol. It challenges the assumption that a person’s appearance or lifestyle…Specification 1.12 · 1.18(i) · 1.18(ii) · 1.19Read & use the scienceClose article
Why this matters
Familial hypercholesterolaemia is an inherited condition in which the body’s handling of cholesterol leads to high LDL cholesterol. It challenges the assumption that a person’s appearance or lifestyle reveals their cardiovascular risk. Studying inherited changes that affect cholesterol regulation also helps researchers investigate whether LDL is merely associated with disease or contributes causally to it. For students, this brings together genes, lipid transport and evidence. A useful assessment must consider measured LDL, family history and other factors rather than treating BMI as a complete answer. The condition also illustrates why a mechanism can inform screening of relatives.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.12 know how factors such as genetics, diet, age, gender, high blood pressure, smoking and inactivity increase the risk of cardiovascular disease (CVD)
- 1.18(i) be able to analyse data on the possible significance for health of blood cholesterol levels and levels of high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs)
- 1.18(ii) know the evidence for a causal relationship between blood cholesterol levels (total cholesterol and LDL cholesterol) and cardiovascular disease (CVD)
- 1.19 understand how people use scientific knowledge about the effect of diet, including obesity indicators, such as body mass index and waist-to-hip ratio, exercise and smoking to reduce their risk of coronary heart disease
Use the science
Why might a physically active person with a low BMI still have high cardiovascular risk associated with LDL cholesterol?
Explore a possible response
An inherited change can impair cholesterol regulation or removal independently of those indicators. BMI and activity do not measure LDL or eliminate genetic risk.
Explore the source
Go to the lesson: Diet and Cardiovascular Health →The test is the outcome
1C · Dietary Antioxidants and Cardiovascular DiseaseA Cochrane review of antioxidant supplement trials found no general mortality benefit and identified potential harms for some supplements. Its scope is supplements and mortality, rather than proving…Specification 1.13 · 1.15Read & use the scienceClose article
Why this matters
A Cochrane review of antioxidant supplement trials found no general mortality benefit and identified potential harms for some supplements. Its scope is supplements and mortality, rather than proving that fruit and vegetables lack value. The displayed Cochrane summary was published in 2021, but the reported search for this review ended in February 2011: publication and evidence-search dates are different. The important reasoning is that an appealing antioxidant mechanism does not establish a survival benefit. Researchers must measure relevant outcomes, include adverse effects and consider trial quality. The result should not be stretched into a claim about all foods, all doses or every future intervention. This is evidence evaluation, rather than advice to start or stop a supplement.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.13 understand the link between dietary antioxidants and the risk of cardiovascular disease (CVD)
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
Use the science
Why should a reviewer report adverse outcomes as well as the proposed benefit?
Explore a possible response
A proposed benefit cannot determine the overall balance if harms are ignored. A treatment or supplement can affect multiple processes and outcomes.
Explore the source
Go to the lesson: Dietary Antioxidants and Cardiovascular Disease →Does the vitamin C on the label survive?
1C · Dietary Antioxidants and Cardiovascular DiseaseA food scientist must consider what happens between harvesting, processing, storage and consumption. Vitamin C content can decrease during prolonged storage and cooking; its water solubility also matters…Specification 1.14 · 1.13Read & use the scienceClose article
Why this matters
A food scientist must consider what happens between harvesting, processing, storage and consumption. Vitamin C content can decrease during prolonged storage and cooking; its water solubility also matters when food is cooked in water. Your vitamin C investigation therefore models a real quality-control problem, provided the sampling and measurement are reliable. A comparison should use equivalent portions, a consistent endpoint and repeated measurements rather than assuming a label describes every sample at every time. This application also connects food preservation with waste: maintaining quality has value, but any proposed process needs evidence about nutrients, safety and resource use.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.14 CORE PRACTICAL 2 Investigate the vitamin C content of food and drink.
- 1.13 understand the link between dietary antioxidants and the risk of cardiovascular disease (CVD)
Use the science
How would you distinguish vitamin C lost from vegetables into cooking water from vitamin C chemically destroyed during cooking?
Explore a possible response
Measure matched starting material, cooked tissue and the cooking water with suitable controls, accounting for total amounts and volumes rather than comparing concentrations alone.
Explore the source
- Vitamin C: Health Professional Fact SheetNIH Office of Dietary Supplements
Turning many papers into a useful conclusion
1C · Using the EvidenceResearchers who synthesise evidence turn a collection of studies into a structured assessment of a health question. Cochrane explains how systematic reviews aim to reduce bias in finding…Specification 1.15 · 1.16Read & use the scienceClose article
Why this matters
Researchers who synthesise evidence turn a collection of studies into a structured assessment of a health question. Cochrane explains how systematic reviews aim to reduce bias in finding and evaluating that evidence. Evidence-synthesis researchers define a question and search systematically, rather than selecting the papers that fit a preferred answer. They compare designs, populations, outcomes and possible sources of bias before deciding whether results can reasonably be combined. A large but poorly controlled study and a small randomised trial do not answer exactly the same question. This makes evidence synthesis a scientific task: judge how each result was obtained and what it measures, rather than treating agreement as a majority vote.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Why is “six studies agree and four disagree” an incomplete summary?
Explore a possible response
Studies differ in size, quality, precision, populations and outcomes. Counting them equally can hide these differences and selective publication.
Explore the source
- Chapter 1: Starting a reviewCochrane
Half a million volunteers can still be biased
1C · Using the EvidenceLarge biobanks let epidemiologists investigate relationships between health, genes and behaviour. But people who volunteer may differ from those who do not. A 2024 study explored how weighting…Specification 1.15 · 1.16Read & use the scienceClose article
Why this matters
Large biobanks let epidemiologists investigate relationships between health, genes and behaviour. But people who volunteer may differ from those who do not. A 2024 study explored how weighting UK Biobank participants using population information changed estimated associations. Weighting gives different influence to records to better represent a target population; it is not a magical repair for every missing variable. This takes sample selection beyond the instruction to use more people. Increasing sample size can reduce random uncertainty while leaving systematic bias intact. An epidemiologist must ask whose lives are represented before interpreting a precise-looking result.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Why can adding more participants recruited by the same biased method narrow a confidence interval without making the estimate closer to the population value?
Explore a possible response
More observations reduce sampling variation but do not necessarily remove systematic differences between volunteers and the target population.
Explore the source
- Reweighting UK Biobank corrects for pervasive selection bias due to volunteeringvan Alten et al., International Journal of Epidemiology (2024)
Why “best medicine” needs a context
1C · The Benefits and Risks of TreatmentNHLBI describes several medicine groups used in coronary heart disease, acting on different parts of the disease process. This illustrates why matching a treatment to a clinical situation…Specification 1.20Read & use the scienceClose article
Why this matters
NHLBI describes several medicine groups used in coronary heart disease, acting on different parts of the disease process. This illustrates why matching a treatment to a clinical situation requires more than knowing one mechanism. A medicine reducing platelet aggregation targets a different step from one lowering blood pressure or cholesterol. The expected benefit also depends on the person’s starting risk and the outcome being prevented. For a clinical researcher, the question is not just whether a mechanism works, but how often important benefits and harms occur in an appropriate comparison group. This makes the specification’s evaluation of benefits and risks practical: a plausible action alone cannot identify the best treatment for everyone.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.20 know the benefits and risks of treatments for cardiovascular disease (CVD) (antihypertensives, statins, anticoagulants and platelet inhibitors)
Use the science
Why is “this medicine prevents clots, so everyone should take it” an unjustified claim?
Explore a possible response
Baseline clot risk varies, while medicines can cause harms such as bleeding. Evidence from one patient group may not apply to everyone, and individual decisions need clinical assessment.
Explore the source
Go to the lesson: The Benefits and Risks of Treatment →Testing a side effect without dismissing it
1C · The Benefits and Risks of TreatmentThe SAMSON trial studied people who had stopped statins because of symptoms. Participants experienced periods with statin tablets, placebo tablets and no tablets, allowing researchers to compare symptom…Specification 1.16 · 1.20Read & use the scienceClose article
Why this matters
The SAMSON trial studied people who had stopped statins because of symptoms. Participants experienced periods with statin tablets, placebo tablets and no tablets, allowing researchers to compare symptom patterns within individuals. Symptoms during placebo and statin periods were similar on average. This illustrates the nocebo effect: expectations and the experience of treatment can contribute to symptoms. The symptoms are real; the result does not mean every adverse reaction is imagined or that statins cannot cause harm. The study shows why evaluating a treatment requires a suitable comparison and attention to the population actually recruited.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
- 1.20 know the benefits and risks of treatments for cardiovascular disease (CVD) (antihypertensives, statins, anticoagulants and platelet inhibitors)
Use the science
What does the no-tablet period help distinguish that a statin-versus-placebo comparison alone cannot?
Explore a possible response
It helps separate background symptoms from symptoms associated with taking a tablet and treatment expectations. A placebo arm alone cannot quantify the no-tablet baseline.
Explore the source
- Side Effect Patterns in a Crossover Trial of Statin, Placebo, and No TreatmentHoward et al., Journal of the American College of Cardiology (2021)
Measuring function rather than guessing
1C · Thinking Bigger: Heart FailureNHLBI describes heart failure as a problem with the heart’s ability to supply the body. Measurements help connect symptoms to mechanisms. Heart rate counts beats, whereas cardiac output…Specification 1.6 · 1.8Read & use the scienceClose article
Why this matters
NHLBI describes heart failure as a problem with the heart’s ability to supply the body. Measurements help connect symptoms to mechanisms. Heart rate counts beats, whereas cardiac output describes the volume moved each minute. The same rate can accompany different stroke volumes, and tissues depend on adequate delivery rather than the count alone. Cardiac physiology therefore uses measurements that address pumping and filling as well as rhythm. This is an application of transport biology, not a diagnostic exercise. A numerical change needs a physiological interpretation and a comparison with other observations before it can explain someone’s symptoms.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
Use the science
Why might measuring heart rate alone miss a pumping problem?
Explore a possible response
It does not measure the volume ejected per beat or whether the blood flow meets tissue needs.
Explore the source
- NHLBI: heart failureNHLBI
A channel with a measurable job
2A · Cell MembranesThe CFTR protein forms an ion channel in cell membranes. Investigating its function links a molecular component to transport across a cell surface. A researcher can separate several…Specification 2.2(i) · 2.5(ii)Read & use the scienceClose article
Why this matters
The CFTR protein forms an ion channel in cell membranes. Investigating its function links a molecular component to transport across a cell surface. A researcher can separate several questions: was CFTR synthesised, did it reach the cell surface, and does the channel open and conduct ions? Different experiments are needed for each. A fluorescent signal somewhere inside a cell might establish the presence of a tagged protein without establishing normal transport. This extends the fluid-mosaic model into a measurable problem: membranes are organised working systems, and the location and activity of an embedded protein matter as much as its presence.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.2(i) know the structure and properties of cell membranes
- 2.5(ii) understand the involvement of carrier and channel proteins in membrane transport
Use the science
Why would knowing that a cell makes a protein be insufficient to show that it functions as a surface channel?
Explore a possible response
It must also reach the correct membrane, adopt an appropriate structure and permit transport under the relevant conditions. Protein production alone does not establish location or function.
Explore the source
- Cystic Fibrosis Foundation: basics of CFTRCystic Fibrosis Foundation
Getting a message through a membrane
2A · Cell MembranesAn RNA medicine must reach the part of a cell where it can work. Large, charged RNA molecules do not simply diffuse through the hydrophobic interior of a…Specification 2.2(i) · 2.5(i)Read & use the scienceClose article
Why this matters
An RNA medicine must reach the part of a cell where it can work. Large, charged RNA molecules do not simply diffuse through the hydrophobic interior of a membrane. Lipid nanoparticles help carry the cargo into cells, but uptake is only one hurdle: RNA can remain trapped in an endosome, a membrane-bound compartment formed during entry. A 2025 imaging study investigated several barriers between uptake and release into the cytosol. It found that membrane damage did not automatically mean useful RNA delivery. This makes membrane structure a practical research problem rather than just a diagram to label.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.2(i) know the structure and properties of cell membranes
- 2.5(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis
Use the science
A fluorescent signal shows nanoparticles inside a cell. Why does that not demonstrate that their RNA has reached ribosomes?
Explore a possible response
The particles or RNA may remain in endosomes; an intracellular location is not necessarily the cytosol. Cargo-specific localisation or functional translation measurements are needed.
Explore the source
- Cellular and biophysical barriers to lipid nanoparticle mediated delivery of RNA to the cytosolNature Communications (2025)
Why “stronger alcohol” is not the whole answer
2A · Cell MembranesAlcohol changes the behaviour of biological materials, which is why it appears in your membrane-permeability practical and in disinfectant research. But more concentrated does not automatically mean more…Specification 2.3 · 2.6(iii)Read & use the scienceClose article
Why this matters
Alcohol changes the behaviour of biological materials, which is why it appears in your membrane-permeability practical and in disinfectant research. But more concentrated does not automatically mean more effective. The CDC describes protein denaturation as a major explanation for alcohol’s antimicrobial action and notes the importance of water. This prevents a common overinterpretation of a school experiment: pigment leaking from beetroot demonstrates a change in permeability under those conditions, not that a particular preparation kills every microorganism. Testing a real disinfectant requires a defined organism, exposure time and measure of survival as well as a plausible molecular mechanism.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.3 CORE PRACTICAL 3 Investigate membrane properties including the effect of alcohol and temperature on membrane permeability.
- 2.6(iii) understand the significance of a protein’s primary structure in determining its secondary structure, three-dimensional structure and properties (globular and fibrous proteins and the types of bonds involved in its three-dimensional structure)
Use the science
Why would greater pigment leakage from beetroot be insufficient evidence that a disinfectant is more effective at killing bacteria?
Explore a possible response
Pigment leakage measures plant-tissue permeability, not bacterial survival. Cell type, target structures, exposure conditions and the measured endpoint differ.
Explore the source
- Chemical Disinfectants: AlcoholCDC, Guideline for Disinfection and Sterilization
A membrane as part of a treatment system
2A · Cell Transport and DiffusionHaemodialysis passes blood through a filter and uses dialysis fluid to help remove wastes. Selective exchange across a membrane is central to the process. Fresh dialysis fluid helps…Specification 2.5(i)Read & use the scienceClose article
Why this matters
Haemodialysis passes blood through a filter and uses dialysis fluid to help remove wastes. Selective exchange across a membrane is central to the process. Fresh dialysis fluid helps maintain a concentration difference for suitable waste solutes, while the membrane restricts movement of larger components such as blood cells. If both sides approached the same waste concentration, net diffusion would slow even though individual molecules continued moving. Renal technology must coordinate fluid composition and flow rather than rely on a membrane alone. Water removal also involves a controlled pressure difference, so explaining every part of the treatment as osmosis would miss an important mechanism.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.5(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis
Use the science
Why would continually replacing dialysis fluid help remove a diffusible waste solute more effectively than leaving the same fluid beside the blood?
Explore a possible response
Waste entering unchanged fluid raises its concentration and reduces the concentration difference across the membrane. Replacing it with fluid low in that waste maintains the gradient, sustaining net diffusion out of the blood. Molecules still move both ways; net movement depends on the difference. Pressure-controlled water removal is a separate part of the system.
Explore the source
- NIDDK: haemodialysisNIDDK
Why some medicines work as a patch
2A · Cell Transport and DiffusionA transdermal patch supplies a medicine across the skin over time. Pharmaceutical scientists must match the molecule and formulation to a demanding barrier: the outer skin layer contains…Specification 2.5(i) · 2.2(i)Read & use the scienceClose article
Why this matters
A transdermal patch supplies a medicine across the skin over time. Pharmaceutical scientists must match the molecule and formulation to a demanding barrier: the outer skin layer contains cells surrounded by lipids. Small molecules with suitable lipid solubility can diffuse through more readily than many large or strongly water-soluble molecules. The skin is a tissue, not a single cell membrane, but the principles of gradients and permeability still apply. This explains why changing a tablet into a patch is not a simple packaging decision. Delivery rate, dose and sustained performance must be measured for the particular drug and system.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.5(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis
- 2.2(i) know the structure and properties of cell membranes
Use the science
Why might two drugs with the same concentration in a patch cross the skin at different rates?
Explore a possible response
Their sizes and chemical properties affect partitioning and permeability. Equal concentration does not imply equal diffusion coefficients or equal delivery through a layered tissue.
Explore the source
- Transdermal drug deliveryPrausnitz and Langer, Nature Biotechnology (2008)
Water has specialised routes
2A · Osmosis: A Special Case of DiffusionThe discovery of aquaporins showed that proteins can provide selective water channels in membranes. This connects membrane structure to the speed of water movement. In the work recognised…Specification 2.4 · 2.5(ii)Read & use the scienceClose article
Why this matters
The discovery of aquaporins showed that proteins can provide selective water channels in membranes. This connects membrane structure to the speed of water movement. In the work recognised by the 2003 Nobel Prize, comparing cells with and without an introduced channel helped test whether that protein increased water permeability. Faster water movement was a functional result, not just an image of a membrane component. Aquaporins provide a route; they do not supply energy to push water against its water-potential gradient. This distinction between permeability and driving force is useful whenever research identifies a new transport protein and claims it changes cell behaviour.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.4 understand what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane, down a water potential gradient
- 2.5(ii) understand the involvement of carrier and channel proteins in membrane transport
Use the science
Would adding more water channels necessarily reverse the direction of osmosis?
Explore a possible response
No. It can change permeability and therefore rate, but net direction still follows the water-potential gradient.
Explore the source
- Nobel Prize: discovery of water channelsNobel Prize
Making drinking water by reversing the usual flow
2A · Osmosis: A Special Case of DiffusionReverse-osmosis plants use pressure and a selectively permeable membrane to separate water from dissolved salts. Without the imposed pressure, water tends to move towards the more concentrated solution…Specification 2.4Read & use the scienceClose article
Why this matters
Reverse-osmosis plants use pressure and a selectively permeable membrane to separate water from dissolved salts. Without the imposed pressure, water tends to move towards the more concentrated solution under otherwise comparable conditions. The pressure contribution to water potential changes that situation, allowing a net flow towards the freshwater side. Engineers have to balance water recovery against energy use, membrane performance and the concentrated brine left behind. This is a useful local and global water-supply application of osmosis, but it is not a biological carrier pump using ATP. The membrane and the external energy supply play different roles.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.4 understand what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane, down a water potential gradient
Use the science
If the pressure supply stopped, why would the same membrane not continue producing freshwater at the same rate and direction?
Explore a possible response
The pressure contribution that drives reverse flow would be lost; the remaining water-potential difference would favour ordinary osmotic movement towards the saltier side.
Explore the source
- DesalinationUS Geological Survey
Why rehydration research uses transport biology
2A · Active TransportOral rehydration salts contain a defined glucose–electrolyte mixture. Their use connects intestinal solute absorption with water movement; the formulation is not simply a claim that “more sugar is…Specification 2.5(i) · 2.5(ii) · 2.4Read & use the scienceClose article
Why this matters
Oral rehydration salts contain a defined glucose–electrolyte mixture. Their use connects intestinal solute absorption with water movement; the formulation is not simply a claim that “more sugar is better”. The WHO formulation illustrates why quantities and combinations matter. Sodium and glucose can enter intestinal cells together using a sodium gradient; an ATP-dependent pump helps maintain that gradient, and water follows changes in water potential. The cotransporter itself need not split ATP. This is an extension of the transport model, not a recipe for making a treatment at home. It shows how researchers combine several mechanisms to design a tested formulation rather than treating a single ingredient as a cure.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.5(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis
- 2.5(ii) understand the involvement of carrier and channel proteins in membrane transport
- 2.4 understand what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane, down a water potential gradient
Use the science
Why can an indirectly energy-dependent uptake process slow when ATP production is inhibited?
Explore a possible response
The pump maintaining the driving ion gradient can slow, so the gradient becomes weaker and can no longer support the same uptake. The cotransporter need not hydrolyse ATP directly.
Explore the source
Go to the lesson: Active Transport →A medicine that blocks a glucose carrier
2A · Active TransportSome medicines lower blood glucose by changing what happens in the kidney rather than by supplying insulin. Empagliflozin inhibits a sodium–glucose cotransporter, reducing glucose reabsorption so more glucose…Specification 2.5(i) · 2.5(ii)Read & use the scienceClose article
Why this matters
Some medicines lower blood glucose by changing what happens in the kidney rather than by supplying insulin. Empagliflozin inhibits a sodium–glucose cotransporter, reducing glucose reabsorption so more glucose leaves in urine. A cotransporter couples the movement of two substances; this extends your knowledge of carrier proteins and energy-dependent transport. The glucose transporter does not have to split ATP itself for the process to depend indirectly on energy used to maintain an ion gradient. Blocking one transport route can therefore alter the movement of a different molecule. Detailed kidney anatomy and prescribing decisions are beyond this lesson.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.5(i) understand what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP as an immediate source of energy), endocytosis and exocytosis
- 2.5(ii) understand the involvement of carrier and channel proteins in membrane transport
Use the science
If a glucose carrier is inhibited, does that necessarily mean the phospholipid bilayer has become more permeable to glucose? Explain.
Explore a possible response
No. Carrier-mediated transfer can decrease while the lipid barrier remains unchanged. A change in transport rate does not by itself identify a change in bilayer permeability.
Explore the source
Go to the lesson: Active Transport →An artificial lung still needs gradients
2A · The Need for Gas Exchange SurfacesECMO circulates blood through an artificial lung to add oxygen and remove carbon dioxide before returning blood to the body. Designing an exchange surface requires control of flow…Specification 2.1(i) · 2.1(ii)Read & use the scienceClose article
Why this matters
ECMO circulates blood through an artificial lung to add oxygen and remove carbon dioxide before returning blood to the body. Designing an exchange surface requires control of flow and diffusion conditions. The clinical overview describes the device; applying Fick’s law is the student’s explanatory model. A large exchange area and a thin barrier help, but blood and gas flow must also sustain the relevant differences across that barrier. This gives a biomedical engineer several variables to investigate together. A successful device cannot be judged by area alone, just as a lung cannot be judged only by its size. It must exchange gases effectively while operating as part of a circulation.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.1(i) know the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface and difference in concentration)
- 2.1(ii) understand how the rate of diffusion is dependent on these properties and can be calculated using Fick’s Law of Diffusion
Use the science
Why would a large membrane area alone not guarantee rapid gas transfer?
Explore a possible response
Transfer also depends on the barrier’s permeability and thickness, the gas difference across it and the flows maintaining that difference. A large area cannot compensate for every other limitation.
Explore the source
Go to the lesson: The Need for Gas Exchange Surfaces →A lung interface on a microchip
2A · The Need for Gas Exchange SurfacesResearchers built a small device with human lung and blood-vessel cells on opposite sides of a flexible membrane. They could expose one side to air and the other…Specification 2.1(i) · 2.1(ii)Read & use the scienceClose article
Why this matters
Researchers built a small device with human lung and blood-vessel cells on opposite sides of a flexible membrane. They could expose one side to air and the other to flowing liquid, and apply stretching movements. The aim was to model selected properties of the lung interface for experiments, not to make an entire replacement lung. The design makes familiar variables experimental choices: barrier thickness, movement and exposure can be controlled and measured. A bioengineer asks which features must be reproduced for the scientific question being investigated, and which missing features limit what the model can tell us.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.1(i) know the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface and difference in concentration)
- 2.1(ii) understand how the rate of diffusion is dependent on these properties and can be calculated using Fick’s Law of Diffusion
Use the science
If a model’s exchange barrier were much thicker than the real lung barrier, what effect would you predict on diffusion, assuming other factors were held constant?
Explore a possible response
A longer diffusion distance should reduce transfer rate under Fick’s law. A model may still answer some questions, but absolute rates need careful interpretation.
Explore the source
- Reconstituting Organ-Level Lung Functions on a ChipHuh et al., Science (2010)
Why a larger air space can exchange less gas
2A · The Mammalian Gas Exchange SystemEmphysema involves damage to alveolar walls and loss of effective exchange structure. Joining small spaces into larger ones can reduce total surface area despite leaving air-filled volume. A…Specification 2.1(iii) · 2.1(ii)Read & use the scienceClose article
Why this matters
Emphysema involves damage to alveolar walls and loss of effective exchange structure. Joining small spaces into larger ones can reduce total surface area despite leaving air-filled volume. A physiologist might compare measurements of lung volume with measures of gas transfer and airflow. Those measurements need not change together: more space is not automatically more working surface. Loss of walls also changes the organisation of the exchange region, so an analogy with inflating a healthy balloon can mislead. Applying area, diffusion distance and maintained gradients explains why an anatomical observation needs functional testing. The classroom model helps frame questions; it does not diagnose an individual’s lung disease.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.1(iii) understand how the structure of the mammalian lung is adapted for rapid gaseous exchange
- 2.1(ii) understand how the rate of diffusion is dependent on these properties and can be calculated using Fick’s Law of Diffusion
Use the science
Why is “there is still plenty of air inside” insufficient evidence that a damaged lung exchanges oxygen normally?
Explore a possible response
The amount of air does not establish the available surface area, barrier properties, ventilation pattern or blood supply. Effective transfer requires suitable structure and maintained gradients.
Explore the source
Go to the lesson: The Mammalian Gas Exchange System →Why wildfire smoke can reach deep into a lung
2A · The Mammalian Gas Exchange SystemWildfire smoke contains particles of different sizes. The smallest particles can reach lower regions of the respiratory tract, including the alveolar region, where the thin exchange surface normally…Specification 2.1(iii) · 2.1(ii)Read & use the scienceClose article
Why this matters
Wildfire smoke contains particles of different sizes. The smallest particles can reach lower regions of the respiratory tract, including the alveolar region, where the thin exchange surface normally supports rapid gas transfer. The EPA describes how deposited particles can provoke inflammation and other biological effects. Exposure depends on particle concentration, duration and breathing pattern, not simply whether smoke is visible. This connects lung architecture with environmental monitoring: a feature that benefits oxygen uptake also places delicate tissue in contact with inhaled material. Evidence about exposure and tissue response is needed before turning an air-quality measurement into a health prediction.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.1(iii) understand how the structure of the mammalian lung is adapted for rapid gaseous exchange
- 2.1(ii) understand how the rate of diffusion is dependent on these properties and can be calculated using Fick’s Law of Diffusion
Use the science
Two people spend the same time in air with the same particle concentration, but one is exercising. Why might their inhaled particle doses differ?
Explore a possible response
Exercise can increase ventilation, so a larger volume of air and more particles are inhaled. Deposition also depends on particle properties and breathing route.
Explore the source
- Why is Smoke a Health Concern?US Environmental Protection Agency
Joining exposure data to biology
2A · Thinking Bigger: Asthma and Air PollutionNHLBI identifies air pollution among possible asthma triggers. Environmental health research links measurements of exposure with biological outcomes. Suppose a fictional survey finds more reported wheezing near a…Specification 2.1(iii) · 1.15 · 1.16Read & use the scienceClose article
Why this matters
NHLBI identifies air pollution among possible asthma triggers. Environmental health research links measurements of exposure with biological outcomes. Suppose a fictional survey finds more reported wheezing near a busy road. The association suggests a question; it does not establish that traffic pollution caused every symptom. Researchers would need comparable exposure measurements, consistent symptom definitions and information about alternative explanations such as smoking exposure. Narrowed airways can reduce ventilation, connecting the population pattern to a plausible biological mechanism. Keeping the mechanism separate from the strength of the study is essential when interpreting environmental health headlines.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.1(iii) understand how the structure of the mammalian lung is adapted for rapid gaseous exchange
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
A fictional survey finds more self-reported wheezing near a busy road than farther away. What measurements and comparisons would help test a pollution explanation, and why could narrowed airways affect gas exchange?
Explore a possible response
Measure pollution over comparable periods and record symptoms consistently in comparable groups. Consider smoking exposure, age and other confounders. Narrowed airways can reduce ventilation and maintenance of the oxygen gradient at exchange surfaces. A plausible mechanism supports investigation but does not remove confounding or prove causation in this survey.
Explore the source
Go to the lesson: Thinking Bigger: Asthma and Air Pollution →Catalysis in the washing machine
2B · EnzymesEnzyme manufacturers develop detergent enzymes for effective washing at lower temperatures. This is an application of catalysis under conditions where uncatalysed breakdown of stains would be slower. A…Specification 2.7(i) · 2.7(ii) · 2.8Read & use the scienceClose article
Why this matters
Enzyme manufacturers develop detergent enzymes for effective washing at lower temperatures. This is an application of catalysis under conditions where uncatalysed breakdown of stains would be slower. A protease acts on protein stains, while other enzymes have different substrates: a single catalyst does not digest every kind of dirt. Temperature and pH affect performance, and the whole wash includes water, detergent and mechanical action. The manufacturer source describes commercial applications; the American Chemical Society explanation offers an additional chemistry perspective. To assess an environmental claim, compare equivalent cleaning outcomes and the energy actually used. Merely including an enzyme cannot establish the total impact of a product.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.7(i) understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure
- 2.7(ii) understand that enzymes are biological catalysts that reduce activation energy
- 2.8 CORE PRACTICAL 4 Investigate the effect of temperature, pH, enzyme concentration and substrate concentration on the initial rate of enzyme-catalysed reactions.
Use the science
A detergent advertisement claims “enzyme-powered” automatically means a lower environmental impact. What additional evidence would you request?
Explore a possible response
Comparable cleaning performance, the temperatures and energy actually used, dosage, manufacture and other lifecycle effects. The presence of a catalyst alone does not quantify the overall impact.
Explore the sources
- Novonesis: enzyme-based laundry applications (manufacturer source)Novonesis
- The Chemistry of Cold-Water WashingAmerican Chemical Society, inChemistry (2024)
Can an enzyme recycle a plastic bottle?
2B · EnzymesResearchers engineered FAST-PETase, an enzyme that breaks bonds in the polyester PET, and tested it on several post-consumer products. The work linked changes in amino-acid sequence with useful…Specification 2.7(i) · 2.7(ii) · 2.8Read & use the scienceClose article
Why this matters
Researchers engineered FAST-PETase, an enzyme that breaks bonds in the polyester PET, and tested it on several post-consumer products. The work linked changes in amino-acid sequence with useful activity under selected temperature and pH conditions. That is an extension of enzyme specificity and experimental rate measurements, not evidence that one enzyme digests every plastic. PET products also differ in structure and accessibility, so results depend on the material tested and any pretreatment. Recovering monomers can make chemical recycling possible, but an industrial process must additionally account for energy, separation, enzyme production and repeated performance.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.7(i) understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure
- 2.7(ii) understand that enzymes are biological catalysts that reduce activation energy
- 2.8 CORE PRACTICAL 4 Investigate the effect of temperature, pH, enzyme concentration and substrate concentration on the initial rate of enzyme-catalysed reactions.
Use the science
Why would an enzyme that hydrolyses PET not necessarily break down polyethylene, even though both are called plastics?
Explore a possible response
Their chemical structures and bonds differ. An enzyme’s active site and catalytic mechanism are specific; polyethylene lacks PET’s ester linkages.
Explore the source
- Machine learning-aided engineering of hydrolases for PET depolymerizationLu et al., Nature (2022)
Selecting enzymes for a new task
2B · How Enzymes WorkFrances Arnold’s directed evolution of enzymes was recognised in the 2018 Nobel Prize in Chemistry. Researchers generate variants and screen their performance, retaining variants useful under the chosen…Specification 2.7(i) · 2.8Read & use the scienceClose article
Why this matters
Frances Arnold’s directed evolution of enzymes was recognised in the 2018 Nobel Prize in Chemistry. Researchers generate variants and screen their performance, retaining variants useful under the chosen conditions. “Better” must be defined by the test: greater initial activity, longer stability or useful activity in a new solvent are different targets. A variant chosen under one set of conditions may perform poorly in another. This connects the Raw Enzymes extension to a real research method without duplicating its content. Researchers do not instruct a protein to improve; they create variation and use measurements to select it. The assay determines which properties are rewarded and which trade-offs may remain hidden.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.7(i) understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure
- 2.8 CORE PRACTICAL 4 Investigate the effect of temperature, pH, enzyme concentration and substrate concentration on the initial rate of enzyme-catalysed reactions.
Use the science
Why should an enzyme selected for activity at one temperature also be tested under the conditions of its intended use?
Explore a possible response
A useful change in one condition may not improve performance in another. Temperature, pH, substrates and stability requirements can differ, so selection results are conditional on the assay.
Explore the sources
- Nobel Prize: directed evolution of enzymesNobel Prize
- Innovation by Evolution: Bringing New Chemistry to LifeFrances H. Arnold, Nobel Lecture (2018)
The enzyme inside a glucose sensor
2B · How Enzymes WorkMany glucose sensors use an enzyme reaction to turn a chemical concentration into an electrical signal. The enzyme helps the device respond to its target, while calibration connects…Specification 2.7(i) · 2.8Read & use the scienceClose article
Why this matters
Many glucose sensors use an enzyme reaction to turn a chemical concentration into an electrical signal. The enzyme helps the device respond to its target, while calibration connects the measured signal with concentration. This makes specificity, reaction conditions and the useful measurement range engineering problems. A sensor that works well in one test solution may behave differently when temperature changes or interfering substances are present. The laboratory scientists developing it must test performance across realistic conditions and compare results with a reference method. Enzyme biology therefore helps explain both the power and the limitations of a familiar medical technology.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.7(i) understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure
- 2.8 CORE PRACTICAL 4 Investigate the effect of temperature, pH, enzyme concentration and substrate concentration on the initial rate of enzyme-catalysed reactions.
Use the science
Why could a change in temperature alter a sensor’s output even if the sample’s glucose concentration stays the same?
Explore a possible response
Temperature can affect the enzyme’s reaction rate and hence signal generation. Calibration or compensation is needed to separate concentration from other influences.
Explore the source
- Glucose biosensors in clinical practice: principles, limits and perspectives of currently used devicesPullano et al., Theranostics (2022)
Shakespeare written in DNA
2B · The Structure of DNA and RNAIn 2013, an EMBL-EBI research team reported storing digital files, including Shakespeare’s sonnets, in synthetic DNA and reconstructing the files after reading the DNA sequence. Researchers used a…Specification 2.9(i)Read & use the scienceClose article
Why this matters
In 2013, an EMBL-EBI research team reported storing digital files, including Shakespeare’s sonnets, in synthetic DNA and reconstructing the files after reading the DNA sequence. Researchers used a designed encoding system to translate digital information into a sequence of bases. This was a research demonstration, not evidence that DNA had replaced ordinary storage devices. Reading a sequence correctly is only part of the task: the coding scheme must preserve order and allow the original file to be reconstructed. Knowing the proportions of the four bases would lose most of that information, just as counting letters cannot recover a play. The cultural connection therefore tests a precise biological idea: a repeated backbone can carry information through a variable, ordered sequence.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.9(i) know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, adenine, cytosine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked by condensation reactions to form phosphodiester bonds)
Use the science
Would knowing only the percentages of A, T, C and G let you reconstruct a stored sonnet? Explain using DNA structure.
Explore a possible response
No. Many different base sequences have the same overall percentages. The ordered sequence, together with the encoding rules, is needed to recover the information; composition alone loses that order.
Explore the source
Go to the lesson: The Structure of DNA and RNA →Jurassic Park needs more than an amber mosquito
2B · The Structure of DNA and RNAJurassic Park imagines recovering dinosaur DNA from ancient insects and filling missing sequence with DNA from another animal. The Natural History Museum explains why that premise faces severe…Specification 2.9(i) · 2.9(ii)Read & use the scienceClose article
Why this matters
Jurassic Park imagines recovering dinosaur DNA from ancient insects and filling missing sequence with DNA from another animal. The Natural History Museum explains why that premise faces severe problems of preservation. A molecule’s visible surroundings can survive while its DNA has broken down. Even if short fragments remain, a complete genome is an ordered set of sequences, not merely the correct proportions of four bases. Substituting unrelated sequence does not recover information that has been lost. The film is therefore a useful way to distinguish a recognisable fossil, a chemical remnant and a usable genetic template.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.9(i) know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, adenine, cytosine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked by condensation reactions to form phosphodiester bonds)
- 2.9(ii) know how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix
Use the science
Why can complementary base pairing help copy an intact fragment but not reveal the original sequence of an entirely missing region?
Explore a possible response
A surviving template constrains complementary bases. If neither strand of a region survives, the pairing rule supplies no information about the original order there.
Explore the source
- Can we bring back dinosaurs?Natural History Museum
An experiment that separates explanations
2B · How DNA WorksMeselson and Stahl’s 1958 paper tested competing replication models by following nitrogen labels through generations. It remains an example of designing an observation that distinguishes explanations. The wider…Specification 2.10(ii)Read & use the scienceClose article
Why this matters
Meselson and Stahl’s 1958 paper tested competing replication models by following nitrogen labels through generations. It remains an example of designing an observation that distinguishes explanations. The wider research lesson is to look for a prediction on which rival models disagree. An observation can be consistent with an explanation without uniquely supporting it over every competitor. Sampling after another generation added information because the predicted distributions diverged. This is a principle students can carry into unfamiliar investigations: identify what each model predicts before deciding whether a result distinguishes them. The original paper is a landmark source; the replication mechanism itself remains part of the required specification.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.10(ii) understand how Meselson and Stahl’s classic experiment provided new data that supported the accepted theory of replication of DNA and refuted competing theories
Use the science
Why would sampling only before transfer and after one generation leave an important uncertainty?
Explore a possible response
The first intermediate band is compatible with both semi-conservative and dispersive models. Later sampling tests where their predictions diverge.
Explore the source
- Meselson and Stahl: original 1958 paperProceedings of the National Academy of Sciences (1958)
Molecular photocopying has a template problem
2B · How DNA WorksPCR lets laboratory scientists make many copies of a selected DNA region from a small starting sample. It uses repeated rounds of strand separation and DNA synthesis, with…Specification 2.10(i) · 2.9(ii)Read & use the scienceClose article
Why this matters
PCR lets laboratory scientists make many copies of a selected DNA region from a small starting sample. It uses repeated rounds of strand separation and DNA synthesis, with short primers helping select the target. This adapts the template principle and DNA polymerase activity you already know. It does not turn an unknown or missing sequence into the correct original, and copying a contaminant can create a misleading signal. The value of amplification therefore depends on sample handling and controls as well as chemistry. PCR’s detailed stages belong later in the course; here the extension is what template-directed copying can and cannot establish.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.10(i) understand the process of DNA replication, including the role of DNA polymerase
- 2.9(ii) know how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix
Use the science
Why should a reaction containing all the reagents but no intended sample be included when searching for a particular DNA sequence?
Explore a possible response
It can reveal contamination or unintended amplification in reagents or handling. A positive signal is only interpretable against appropriate controls.
Explore the source
- Polymerase Chain Reaction (PCR) Fact SheetNational Human Genome Research Institute
Cracking the code
2B · The Genetic CodeThe 1968 Nobel Prize in Physiology or Medicine recognised Holley, Khorana and Nirenberg for work interpreting the genetic code and its role in protein synthesis. Artificial RNA sequences…Specification 2.11Read & use the scienceClose article
Why this matters
The 1968 Nobel Prize in Physiology or Medicine recognised Holley, Khorana and Nirenberg for work interpreting the genetic code and its role in protein synthesis. Artificial RNA sequences allowed researchers to connect controlled inputs with the polypeptides produced. A repeating U sequence is particularly informative because every triplet is UUU; mixed repeating sequences need more careful interpretation of possible reading frames. This reveals the code as an experimentally tested relationship rather than a table scientists simply assumed. The detailed historical methods are enrichment. The specification connection is the logic of triplet coding and the need for enough experiments to distinguish competing assignments.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.11 understand the nature of the genetic code (triplet code, non-overlapping and degenerate)
Use the science
If an artificial RNA made only of U produced a chain of phenylalanine, what codon assignment would that support?
Explore a possible response
Every complete triplet is UUU, so it supports assigning UUU to phenylalanine. Further experiments are needed for other codons.
Explore the source
- The genetic code: historyNobel Prize
Could a cell use fewer genetic code words?
2B · The Genetic CodeThe genetic code is degenerate: several codons can specify the same amino acid. In 2019, researchers used that redundancy to construct an E. coli genome in which selected…Specification 2.11 · 2.12Read & use the scienceClose article
Why this matters
The genetic code is degenerate: several codons can specify the same amino acid. In 2019, researchers used that redundancy to construct an E. coli genome in which selected codons were replaced with alternatives, producing an organism with a reduced set of codons. This was not a change from triplets to pairs, nor did it mean the bacterium stopped making the usual twenty amino acids. The work also showed why apparently synonymous changes need testing: translation is a biological process, and codon choices can matter to how successfully it runs. Synthetic biology turns a property of the code into a design question.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.11 understand the nature of the genetic code (triplet code, non-overlapping and degenerate)
- 2.12 know that a gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
Use the science
How can replacing a codon change the DNA sequence without changing the amino-acid sequence, and why is that not enough to prove the cell is unaffected?
Explore a possible response
A synonymous codon specifies the same amino acid, but translation efficiency or other sequence-dependent processes can still change. Organism-level function needs testing.
Explore the source
- Total synthesis of Escherichia coli with a recoded genomeFredens et al., Nature (2019) · Abstract
Seeing the protein-making machinery
2B · DNA and Protein SynthesisThe 2009 Nobel Prize in Chemistry recognised studies of the structure and function of the ribosome. Structural biology connects the arrangement of molecules with the reactions they perform.…Specification 2.13(i) · 2.13(ii)Read & use the scienceClose article
Why this matters
The 2009 Nobel Prize in Chemistry recognised studies of the structure and function of the ribosome. Structural biology connects the arrangement of molecules with the reactions they perform. Researchers mapped the positions of components and investigated how molecules, including some antibiotics, interact with the machinery. A structural map helps explain why a molecule can interfere with translation, but it is not by itself proof of a safe and effective medicine. Biological activity and selectivity still need testing. The Unit 1 connection is that reading mRNA, positioning tRNAs and forming peptide bonds depend on a working molecular arrangement, not simply on having the correct genetic message available.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.13(i) understand the process of protein synthesis (transcription and translation), including the role of RNA polymerase, translation, messenger RNA, transfer RNA, ribosomes and the role of start and stop codons
- 2.13(ii) understand the roles of the DNA template (antisense) strand in transcription, codons on messenger RNA and anticodons on transfer RNA
Use the science
Why could a change in a ribosome’s shape interfere with translation even if the mRNA sequence is unchanged?
Explore a possible response
It could disrupt binding or positioning of mRNA and tRNAs, or peptide-bond formation. An intact message still needs working translation machinery.
Explore the source
- The ribosome translates the DNA code into lifeNobel Prize, Chemistry 2009
A medicine written as a temporary message
2B · DNA and Protein SynthesisAn mRNA vaccine supplies instructions that cells can translate into a protein; it does not supply a replacement human genome. Research recognised by the 2023 Nobel Prize showed…Specification 2.9(i) · 2.13(i) · 2.13(ii)Read & use the scienceClose article
Why this matters
An mRNA vaccine supplies instructions that cells can translate into a protein; it does not supply a replacement human genome. Research recognised by the 2023 Nobel Prize showed how modified RNA bases could reduce unwanted inflammatory responses and improve protein production. The underlying connection is translation: ribosomes read codons and transfer RNAs deliver amino acids in a specified order. Producing a useful message also involves its stability and how cells respond to it, not just choosing a protein sequence. This example shows how research into apparently fundamental RNA chemistry helped overcome practical barriers to a medical technology.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.9(i) know the basic structure of mononucleotides (deoxyribose or ribose linked to a phosphate and a base, including thymine, uracil, adenine, cytosine or guanine) and the structures of DNA and RNA (polynucleotides composed of mononucleotides linked by condensation reactions to form phosphodiester bonds)
- 2.13(i) understand the process of protein synthesis (transcription and translation), including the role of RNA polymerase, translation, messenger RNA, transfer RNA, ribosomes and the role of start and stop codons
- 2.13(ii) understand the roles of the DNA template (antisense) strand in transcription, codons on messenger RNA and anticodons on transfer RNA
Use the science
Why would a premature stop codon in the supplied mRNA be expected to change the protein made, even if the cell’s own DNA were unchanged?
Explore a possible response
Ribosomes terminate translation at the stop signal, producing a shorter polypeptide from that message. Altering a supplied RNA template does not require changing genomic DNA.
Explore the source
- The Nobel Prize in Physiology or Medicine 2023: Advanced informationNobel Committee for Physiology or Medicine
A tumour’s sequence is evidence
2C · Gene MutationCancer researchers study DNA changes that may affect cell growth. The NCI describes how genetic changes can arise during cell division and how tumour testing can identify changes…Specification 2.14(i) · 2.14(ii)Read & use the scienceClose article
Why this matters
Cancer researchers study DNA changes that may affect cell growth. The NCI describes how genetic changes can arise during cell division and how tumour testing can identify changes relevant to cancer biology. Sequencing a tumour can reveal changes acquired in a lineage of body cells. Comparing that result with suitable non-tumour material helps distinguish acquired changes from variants present more widely in the body. Even then, finding a difference does not automatically prove it caused the cancer: its effect needs interpretation. Cancer genomics therefore combines molecular measurements with evidence about function. This extends mutation biology into research while avoiding the mistaken inference that every cancer-associated variant must have come from a parent.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.14(i) understand how errors in DNA replication can give rise to mutations (substitution, insertion and deletion of bases)
- 2.14(ii) know that some mutations will give rise to cancer or genetic disorders, but that many mutations will have no observable effect
Use the science
Why does finding a mutation in tumour cells not prove that it was inherited?
Explore a possible response
The mutation could have arisen in a body cell during life. Evidence from appropriate non-tumour cells and inheritance information would be needed.
Explore the source
Go to the lesson: Gene Mutation →A mutation is not automatically a tumour
2C · Gene MutationResearchers sequenced small samples of normal sun-exposed skin and found many mutations, including changes associated with cancer. The tissue was not therefore automatically cancerous. The study connects environmental…Specification 2.14(i) · 2.14(ii)Read & use the scienceClose article
Why this matters
Researchers sequenced small samples of normal sun-exposed skin and found many mutations, including changes associated with cancer. The tissue was not therefore automatically cancerous. The study connects environmental exposure, accumulated DNA changes and the difference between a molecular finding and a disease diagnosis. It also challenges a simplistic story in which any mutation produces an immediately visible effect. Cancer development involves additional changes and cellular context. The samples came from a small number of older people having eyelid surgery, so the results should not be treated as a universal measurement for every tissue or age group.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.14(i) understand how errors in DNA replication can give rise to mutations (substitution, insertion and deletion of bases)
- 2.14(ii) know that some mutations will give rise to cancer or genetic disorders, but that many mutations will have no observable effect
Use the science
Why does finding a cancer-associated mutation in a normal skin sample not prove that the sample is a tumour or that the change will be inherited by a child?
Explore a possible response
Association with cancer does not establish all changes needed for a tumour; tissue behaviour matters. A mutation in somatic skin cells is not automatically present in gametes.
Explore the source
- High burden and pervasive positive selection of somatic mutations in normal human skinMartincorena et al., Science (2015)
Explaining a probability clearly
2C · Patterns of InheritanceGenetic counsellors help people understand genetic conditions, testing and family implications. Their work includes communicating uncertainty and supporting informed choices. A genetic counsellor translates a model into language…Specification 2.15(i) · 2.15(ii)Read & use the scienceClose article
Why this matters
Genetic counsellors help people understand genetic conditions, testing and family implications. Their work includes communicating uncertainty and supporting informed choices. A genetic counsellor translates a model into language a family can use, including what a test can and cannot establish. If two carriers of an autosomal recessive condition have children, the usual model predicts a 25% affected probability for each conception. Earlier outcomes do not use up that probability. Real counselling also considers whether the assumed genotypes and condition are established. The skill is explaining conditional probability accurately while supporting choices, rather than telling a family what decision to make.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.15(i) understand what is meant by the terms gene, allele, genotype, phenotype, recessive, dominant, codominance, homozygote and heterozygote
- 2.15(ii) understand patterns of inheritance, including the interpretation of genetic pedigree diagrams, in the context of monohybrid inheritance
Use the science
How would you explain a 1-in-4 recurrence probability without implying that one of every four children must be affected?
Explore a possible response
Describe it as a 25% chance for each conception under the model; family outcomes can differ from the expected proportions.
Explore the source
Go to the lesson: Patterns of Inheritance →Gattaca: a genotype is not a complete biography
2C · Patterns of InheritanceGattaca imagines a society that sorts people by genetic expectations. Real genetic information can be powerful, but the logic of a single-gene cross should not be applied uncritically…Specification 2.15(i) · 1.12 · 2.18Read & use the scienceClose article
Why this matters
Gattaca imagines a society that sorts people by genetic expectations. Real genetic information can be powerful, but the logic of a single-gene cross should not be applied uncritically to every human characteristic. A polygenic risk score combines information from many variants to estimate a probability; it does not include every environmental influence or predict a person’s complete future. The film provides a starting point for separating genotype, phenotype and social judgement. The scientific question comes first: what does a test actually measure, and with what uncertainty? Ethical decisions become distorted if a probability is presented as destiny.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.15(i) understand what is meant by the terms gene, allele, genotype, phenotype, recessive, dominant, codominance, homozygote and heterozygote
- 1.12 know how factors such as genetics, diet, age, gender, high blood pressure, smoking and inactivity increase the risk of cardiovascular disease (CVD)
- 2.18 be able to identify and discuss the ethical and social issues relating to genetic screening from a range of ethical viewpoints, including religious, moral and social implications
Use the science
Why would a Punnett square for one recessive condition be insufficient to predict an individual’s overall cardiovascular health?
Explore a possible response
A monohybrid cross addresses specified alleles at one locus. Cardiovascular health can involve multiple variants, exposure and behaviour; the cross omits those variables.
Explore the sources
- Polygenic Risk Score (PRS)National Human Genome Research Institute
- Member Picks: GattacaBritish Film Institute
Information should survive a colour change
2C · Sex LinkageThe National Eye Institute explains that many forms of colour vision deficiency are inherited, with common red–green forms linked to X. This makes colour choice relevant when communicating…Specification 2.15(iii)Read & use the scienceClose article
Why this matters
The National Eye Institute explains that many forms of colour vision deficiency are inherited, with common red–green forms linked to X. This makes colour choice relevant when communicating biology. For common inherited red–green forms, an X-linked recessive model helps explain why the pattern differs between people with one X chromosome and those with two. It also makes accessibility a scientific communication issue: a red and green distinction on a pedigree may disappear for some readers. Shapes, line styles and labels preserve meaning independently of hue. The application combines inheritance reasoning with experimental communication, without assuming that every form of colour vision deficiency follows the same genetic pattern.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.15(iii) understand sex linkage on the X chromosome, including red-green colour blindness in humans
Use the science
In a simplified X-linked recessive model, a carrier mother and a father without the condition have children. Explain the probability for their sons, then suggest how to label the pedigree so it works without a red/green distinction.
Explore a possible response
Each son receives Y from the father and one of the mother’s X chromosomes, so each has a 1-in-2 chance of inheriting the affected allele in this model. Use defined shading or symbols and direct genotype labels with a clear key, rather than colour alone. These probabilities apply to the specified inheritance model; not all colour vision conditions follow it.
Explore the source
- National Eye Institute: causes of colour vision deficiencyNational Eye Institute
The royal family tree meets DNA evidence
2C · Sex LinkageHaemophilia in European royal families is a famous pedigree example, but historical descriptions alone did not identify the exact molecular cause. Analysis of Romanov remains identified a likely…Specification 2.15(ii) · 2.15(iii) · 1.11Read & use the scienceClose article
Why this matters
Haemophilia in European royal families is a famous pedigree example, but historical descriptions alone did not identify the exact molecular cause. Analysis of Romanov remains identified a likely disease-causing variant in F9, an X-linked gene involved in blood clotting, supporting haemophilia B. The case shows how a family pattern and sequence evidence answer different questions. A pedigree can suggest how a condition is inherited; molecular analysis can identify a particular candidate change. Factor IX and RNA-splicing details are extension material. The useful Unit 1 connection is the route from X-linked inheritance to a changed protein and clotting function.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.15(ii) understand patterns of inheritance, including the interpretation of genetic pedigree diagrams, in the context of monohybrid inheritance
- 2.15(iii) understand sex linkage on the X chromosome, including red-green colour blindness in humans
- 1.11 understand the blood clotting process (thromboplastin release, conversion of prothrombin to thrombin and fibrinogen to fibrin) and its role in cardiovascular disease (CVD)
Use the science
In a simple X-linked recessive model, why can an affected father pass the variant to daughters but not directly to sons?
Explore a possible response
Daughters inherit his X chromosome, while sons inherit his Y. The mother’s contribution and genotype determine the full outcome for each child.
Explore the source
- Genotype analysis identifies the cause of the “royal disease”Rogaev et al., Science (2009), PubMed abstract · Abstract
One protein, several specialist teams
2C · Cystic Fibrosis: A Genetic DiseaseThe Cystic Fibrosis Foundation describes effects across several organs. Understanding the connections calls on respiratory, nutritional and reproductive expertise rather than treating CF as only a lung condition.…Specification 2.16Read & use the scienceClose article
Why this matters
The Cystic Fibrosis Foundation describes effects across several organs. Understanding the connections calls on respiratory, nutritional and reproductive expertise rather than treating CF as only a lung condition. A molecular defect can have consequences that depend on the tissue in which transport is disturbed. In the airways, altered secretions affect clearance; in the digestive system, obstruction can interfere with delivery of pancreatic enzymes and hence digestion. A dietitian’s nutritional questions and a physiologist’s functional measurements can therefore concern different consequences of the same underlying condition. This is why multidisciplinary thinking matters: explaining the gene or channel alone does not yet explain the full pattern of effects across organs.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.16 understand how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systems
Use the science
Why might a physiologist and a dietitian ask different questions about the same CFTR defect?
Explore a possible response
The physiologist may investigate transport and ventilation; the dietitian may investigate digestion and nutrient absorption. Both trace consequences of the same underlying disorder.
Explore the sources
- Cystic Fibrosis Foundation: about CFCystic Fibrosis Foundation
- Your CF Care TeamCystic Fibrosis Foundation
Why one CF medicine does not fit every mutation
2C · Cystic Fibrosis: A Genetic DiseaseCFTR modulators target defects in the protein rather than only managing the consequences of thick mucus. Correctors can help some CFTR proteins fold and reach the cell surface;…Specification 2.16 · 2.14(ii) · 2.6(iii)Read & use the scienceClose article
Why this matters
CFTR modulators target defects in the protein rather than only managing the consequences of thick mucus. Correctors can help some CFTR proteins fold and reach the cell surface; potentiators improve the activity of channels that are present. The distinction follows directly from sequence, structure and function. A treatment that helps an existing channel open cannot solve the same problem in a cell making no usable channel at all. This is an example of personalised medicine based on the molecular effect of a variant. Improving protein function can help symptoms, but it does not change the inherited DNA sequence.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.16 understand how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systems
- 2.14(ii) know that some mutations will give rise to cancer or genetic disorders, but that many mutations will have no observable effect
- 2.6(iii) understand the significance of a protein’s primary structure in determining its secondary structure, three-dimensional structure and properties (globular and fibrous proteins and the types of bonds involved in its three-dimensional structure)
Use the science
Compare why a potentiator might help a gating defect but not a mutation that prevents any CFTR protein being produced.
Explore a possible response
A gating defect leaves a channel that the drug can act on. With no protein there is no channel target; a different approach is required.
Explore the source
- CFTR Modulator TypesCystic Fibrosis Foundation
What embryo testing can tell you
2C · Genetic ScreeningThe HFEA explains PGT-M as testing embryos for specific monogenic conditions. Its information distinguishes testing from a guarantee of pregnancy or a child without any health condition. An…Specification 2.17(i) · 2.17(ii) · 2.18Read & use the scienceClose article
Why this matters
The HFEA explains PGT-M as testing embryos for specific monogenic conditions. Its information distinguishes testing from a guarantee of pregnancy or a child without any health condition. An embryology laboratory needs a clearly defined testing target and a method suited to the family’s situation. The result addresses that target, not every possible inherited variant or future environmental influence. Technical limitations and uncertainty remain relevant to informed decisions, alongside personal and ethical considerations. Students can separate three questions: what was tested, how reliable is that result, and what does it imply? This prevents the popular phrase “designer baby” from replacing a careful account of what a specific test actually measures.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.17(i) understand the uses of genetic screening, including the identification of carriers, pre-implantation genetic diagnosis (PGD) and prenatal testing, including amniocentesis and chorionic villus sampling
- 2.17(ii) understand the implications of prenatal genetic screening
- 2.18 be able to identify and discuss the ethical and social issues relating to genetic screening from a range of ethical viewpoints, including religious, moral and social implications
Use the science
Why is “an embryo tested for one condition” more accurate than “a guaranteed healthy embryo”?
Explore a possible response
A targeted test addresses specified genetic findings. It cannot rule out every other condition or predict every later health outcome.
Explore the source
Go to the lesson: Genetic Screening →A negative DNA test is not an all-clear for life
2C · Genetic ScreeningA commercial genetic test may examine a selected set of variants rather than every possible disease-associated change. The FDA explains that different companies can test different sets, so…Specification 2.17(i) · 2.18Read & use the scienceClose article
Why this matters
A commercial genetic test may examine a selected set of variants rather than every possible disease-associated change. The FDA explains that different companies can test different sets, so a negative result has to be interpreted within the test’s scope. It does not remove environmental risks, unknown variants or changes that were never tested. This extends genetic screening beyond the technology to the meaning of a result and the claims used to sell it. A scientifically responsible report distinguishes the absence of a detected variant from a guarantee of health, and makes uncertainty visible rather than hiding it in advertising.
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Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 2.17(i) understand the uses of genetic screening, including the identification of carriers, pre-implantation genetic diagnosis (PGD) and prenatal testing, including amniocentesis and chorionic villus sampling
- 2.18 be able to identify and discuss the ethical and social issues relating to genetic screening from a range of ethical viewpoints, including religious, moral and social implications
Use the science
Two companies test different variants for the same condition and return different results. Why does this not by itself prove that one laboratory made an analytical error?
Explore a possible response
Their panels may measure different targets. Different scope can produce different findings even with accurate assays; interpretation also depends on evidence for each variant.