Original, AI-authored English practice with worked guidance. Selected topics only; independent teacher review is pending. This is not a complete syllabus, official past-paper collection or predicted exam score. Check your own exam-board specification: these concepts are not certified against a particular board or exam year.
72 original questions across 15 selected topic areas. No account or payment required to practise.
5 questions in this topic. Exact English revisions checked in an AI-assisted academic review; independent teacher approval is still pending.
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Original English concept practice addressing selected identified gaps. Not complete syllabus coverage or practical competence.
Selected subtopics: Xylem and phloem mechanisms · ABA and auxin responses · Cardiac pressure and excitation · Blood gas transport · Airway defence and alveoli
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Question 1Explain how water reaches a leaf through xylem during transpiration and how sucrose moves from a source leaf to a sink through phloem. Include the Casparian strip, cohesion-tension, companion-cell proton pumps and the pressure gradient. Explain why the two transport mechanisms should not both be called active pumping along the whole vessel.5 indicative marks
Explain using the evidence5 indicative marksNo calculator
Explain how water reaches a leaf through xylem during transpiration and how sucrose moves from a source leaf to a sink through phloem. Include the Casparian strip, cohesion-tension, companion-cell proton pumps and the pressure gradient. Explain why the two transport mechanisms should not both be called active pumping along the whole vessel.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Checked root barrier, water cohesion, explicit 7.2 proton cotransport and pressure-flow distinction; no unsupported claim that sucrose itself is pumped the entire distance. This is conceptual placement, not completion of the entire referenced subsection.
Follow water from root pathways to evaporating leaf surfaces. The Casparian strip prevents a purely cell-wall bypass of endodermal membrane control; the long-distance driving force is supplied by transpiration-related tension.
Follow sucrose separately: loading at a source promotes osmotic water entry and high source pressure. Unloading/use at sinks sustains lower pressure. Different sieve tubes can carry assimilates to different sinks; this does not imply simultaneous opposite mass flows within one continuous tube.
Self-marking points
The endodermal Casparian strip blocks the unrestricted apoplast route so water/solutes must cross selectively permeable membranes before entering the stele.
Evaporation from leaf surfaces and vapour diffusion create tension; cohesion transmits the pull through water in xylem.
Companion-cell proton pumps use ATP to establish a gradient that supports sucrose loading by cotransport.
Loading lowers water potential, water entry raises hydrostatic pressure, and phloem sap mass-flows towards lower-pressure sinks.
Energy-dependent loading is distinct from pressure-driven bulk movement; xylem transport is not a chain of ATP pumps along dead vessels.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
Question 2During water stress a plant raises abscisic acid signalling; in another tissue auxin stimulates elongation. Explain how guard-cell water loss can close stomata, the role of calcium as a second messenger in the ABA response, and how auxin-mediated proton pumping differs from stomatal closure. State the gas-exchange trade-off of closure.4 indicative marks
Explain using the evidence4 indicative marksNo calculator
During water stress a plant raises abscisic acid signalling; in another tissue auxin stimulates elongation. Explain how guard-cell water loss can close stomata, the role of calcium as a second messenger in the ABA response, and how auxin-mediated proton pumping differs from stomatal closure. State the gas-exchange trade-off of closure.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Checked ABA/calcium guard-cell mechanism against 14.2.4 and acid-growth proton pumping against 15.2.2, preserving tissue-specific distinctions. This is conceptual placement, not completion of the entire referenced subsection.
ABA initiates signalling; intracellular calcium can act as a second messenger affecting ion transport. This does not require ABA perception to occur outside the cell. Ion loss changes water potential so water exits guard cells.
For growth, acidification modifies the wall's ability to extend under turgor. The comparison separates a growing-cell elongation mechanism from regulation of a stomatal aperture; it does not claim auxin has only one effect in every tissue.
Self-marking points
ABA signalling can use calcium ions as a second messenger to alter guard-cell ion transport.
Loss of guard-cell solutes is followed by osmotic water loss and reduced turgor, closing the pore.
Closure reduces water-vapour loss but also restricts CO2 entry for photosynthesis.
Auxin stimulates proton pumping that acidifies cell walls and facilitates wall loosening/elongation in growing cells; it is not the same response as ABA-driven guard-cell closure.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
Question 3At one instant left-ventricular pressure is 14 kPa, left-atrial pressure 1 kPa and aortic pressure 12 kPa. Infer the state of the left atrioventricular and aortic valves. Explain normal excitation from sinoatrial node to ventricles and why the left ventricle has a thicker wall than the right.4 indicative marks
Explain using the evidence4 indicative marksNo calculator
At one instant left-ventricular pressure is 14 kPa, left-atrial pressure 1 kPa and aortic pressure 12 kPa. Infer the state of the left atrioventricular and aortic valves. Explain normal excitation from sinoatrial node to ventricles and why the left ventricle has a thicker wall than the right.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Verified pressure inequalities for each valve and volume-versus-pressure distinction in double circulation; no unsupported clinical diagnosis from fictional pressures. This is conceptual placement, not completion of the entire referenced subsection.
Valves respond passively to pressure differences, not direct nervous commands to flap open. Compare the supplied pressures across each valve separately.
The delay between atrial and ventricular activation coordinates filling and ejection. Greater wall thickness supports greater pressure generation, not the false claim that the left ventricle normally pumps more volume per beat than the right.
Self-marking points
The left atrioventricular valve is closed because ventricular pressure exceeds atrial pressure.
The aortic valve is open because ventricular pressure exceeds aortic pressure, consistent with ejection.
The sinoatrial node initiates atrial excitation; atrioventricular delay permits atrial emptying before excitation reaches ventricular tissue through the conduction pathway including Purkyne tissue.
The left ventricle generates the higher pressure needed for systemic circulation; the right pumps through the lower-resistance pulmonary circuit.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
Question 4At the same oxygen partial pressure, haemoglobin saturation is lower in a sample with higher CO2. Explain this Bohr shift and its value in respiring tissue. Outline how red-cell carbonic anhydrase and the chloride shift support carbon-dioxide transport, distinguishing plasma hydrogencarbonate from oxygen bound to haemoglobin.4 indicative marks
Explain using the evidence4 indicative marksNo calculator
At the same oxygen partial pressure, haemoglobin saturation is lower in a sample with higher CO2. Explain this Bohr shift and its value in respiring tissue. Outline how red-cell carbonic anhydrase and the chloride shift support carbon-dioxide transport, distinguishing plasma hydrogencarbonate from oxygen bound to haemoglobin.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Checked fixed-pO2 affinity interpretation, carbonic-anhydrase equation, chloride exchange direction in tissues and distinction between oxygen and CO2 carriage. This is conceptual placement, not completion of the entire referenced subsection.
Compare saturation at the same pO2, not simply samples at different oxygen availability. A right shift means a lower occupied fraction at that fixed pO2.
Write CO2 + H2O <=> H2CO3 <=> H+ + HCO3-. Hydrogencarbonate/chloride exchange preserves electroneutrality while much transported carbon dioxide is represented as plasma HCO3-, not as dissolved oxygen.
Self-marking points
Higher CO2/H+ reduces haemoglobin's oxygen affinity, shifting the dissociation curve right and promoting oxygen unloading.
This helps match greater oxygen delivery to actively respiring tissue.
Carbonic anhydrase accelerates CO2 hydration; dissociation yields H+ and hydrogencarbonate, with H+ buffered partly by haemoglobin.
Hydrogencarbonate moves into plasma while chloride enters red cells to maintain charge balance; oxygen carriage instead mainly involves reversible haem binding.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
Question 5Explain how thin alveolar walls, extensive capillaries and ventilation support gas exchange. Contrast this exchange surface with the functions of airway goblet cells and cilia. A model doubles the effective diffusion distance with all other factors fixed; predict the qualitative effect on diffusion rate without treating this as a diagnosis.4 indicative marks
Explain using the evidence4 indicative marksNo calculator
Explain how thin alveolar walls, extensive capillaries and ventilation support gas exchange. Contrast this exchange surface with the functions of airway goblet cells and cilia. A model doubles the effective diffusion distance with all other factors fixed; predict the qualitative effect on diffusion rate without treating this as a diagnosis.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Verified structure/function and airway-versus-alveolus distinction from 9.1, with a bounded supplied-model diffusion inference rather than unsupported pathology. This is conceptual placement, not completion of the entire referenced subsection.
A short barrier is useful only alongside an available area and concentration/partial-pressure gradients. Blood flow removes absorbed oxygen and supplies carbon dioxide, while ventilation renews alveolar air.
Mucociliary clearance belongs to conducting airways rather than replacing the thin alveolar exchange epithelium. The doubled-distance prediction holds other factors fixed and is not a claim about all consequences of a real disease.
Self-marking points
Thin squamous alveolar epithelium and adjacent thin capillary walls provide a short diffusion path.
Large area and ventilation/perfusion help maintain oxygen and carbon-dioxide gradients.
Goblet cells secrete mucus that traps particles/pathogens; cilia move mucus towards removal from the airways.
Doubling diffusion distance alone decreases diffusion rate; in a simple inverse-distance model it halves it.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
