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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.
Cambridge International AS & A Level Biology (9700), examination year 2027: AI-assisted conceptual alignment to official sources, not teacher or exam-board certification. Syllabus mapping and remaining coverage.
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Original English concept practice addressing selected identified gaps. Not complete syllabus coverage or practical competence.
Selected subtopics: Respiratory quotient · Anaerobic NAD regeneration · Lac operon and DELLA · Sliding-filament coupling
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Question 1A supplied respiratory equation is C16H32O2 + 23O2 -> 16CO2 + 16H2O. Calculate respiratory quotient and compare with complete aerobic glucose respiration, C6H12O6+6O2->6CO2+6H2O. Explain how lactate formation in oxygen-limited muscle permits glycolysis to continue, and why it does not give the full aerobic energy yield.4 indicative marks
Calculate and explain4 indicative marksCalculator allowed
A supplied respiratory equation is C16H32O2 + 23O2 -> 16CO2 + 16H2O. Calculate respiratory quotient and compare with complete aerobic glucose respiration, C6H12O6+6O2->6CO2+6H2O. Explain how lactate formation in oxygen-limited muscle permits glycolysis to continue, and why it does not give the full aerobic energy yield.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Verified atom balance and 16/23 RQ, glucose control ratio and NAD-regeneration role; no invented fixed whole-cell aerobic ATP total. This is conceptual placement, not completion of the entire referenced subsection.
9700: 12.1: ATP, substrates and respiratory quotient
Check the lipid equation's atoms: C16, H32 and O48 occur on both sides. RQ is a molecule/mole ratio, not the mass ratio of gases.
NAD regeneration allows the oxidation step of glycolysis to continue despite loss of aerobic electron disposal. Lactate formation does not independently generate the large ATP yield of the mitochondrial electron-transport pathway.
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RQ = CO2 produced/O2 consumed = 16/23 = 0.696 for the supplied lipid equation.
Glucose RQ = 6/6 = 1.00.
Pyruvate reduction to lactate reoxidises reduced NAD so NAD is available for glycolysis.
Without sustained oxygen-supported oxidative phosphorylation, glycolysis provides a much smaller ATP yield than complete aerobic respiration.
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 2Compare two supplied regulatory cases: lactose prevents a lac repressor from binding its operator, while gibberellin promotes breakdown of DELLA proteins that inhibit transcription-promoting factors. Explain the effect on transcription in each case and distinguish a structural gene from a regulatory gene. Do not invoke cAMP in the lac explanation.4 indicative marks
Explain using the evidence4 indicative marksNo calculator
Compare two supplied regulatory cases: lactose prevents a lac repressor from binding its operator, while gibberellin promotes breakdown of DELLA proteins that inhibit transcription-promoting factors. Explain the effect on transcription in each case and distinguish a structural gene from a regulatory gene. Do not invoke cAMP in the lac explanation.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Checked operator versus gene distinction and specified lac/DELLA mechanisms from 16.3.2-4, including the explicit cAMP exclusion. This is conceptual placement, not completion of the entire referenced subsection.
The operator is a DNA regulatory region, not a gene coding for an enzyme. Lactose-dependent relief of repression is the specified prokaryotic model; cAMP/glucose catabolite detail is expressly not required here.
In the plant example, removing an inhibitory protein can activate a response without the hormone itself being a transcription factor. Subsequent enzyme synthesis can support responses such as barley germination/growth.
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Without bound lac repressor, RNA polymerase can transcribe the lac structural genes when other necessary conditions are met.
The induced structural genes encode proteins involved in lactose use; the regulatory gene encodes a regulatory product such as the repressor.
Gibberellin-mediated DELLA breakdown relieves repression of transcription-promoting factors and permits target-gene activation.
Both cases alter expression of existing information rather than changing the genetic code or directing a new DNA mutation.
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 3Explain how a motor-neurone signal leads to shortening of a striated-muscle sarcomere. Include acetylcholine, T-tubules, sarcoplasmic-reticulum calcium, troponin/tropomyosin and ATP. State which structures slide rather than shortening themselves.5 indicative marks
Explain using the evidence5 indicative marksNo calculator
Explain how a motor-neurone signal leads to shortening of a striated-muscle sarcomere. Include acetylcholine, T-tubules, sarcoplasmic-reticulum calcium, troponin/tropomyosin and ATP. State which structures slide rather than shortening themselves.
Cambridge 2027: Direct conceptual match
Original targeted concept exercise: Checked causal NMJ-to-T-tubule-to-SR sequence and ATP/cross-bridge roles against explicit 15.1.10-12; no hazardous stimulation experiment. This is conceptual placement, not completion of the entire referenced subsection.
Keep the extracellular transmitter and intracellular calcium roles separate. Calcium release inside muscle is not simply acetylcholine entering the sarcoplasmic reticulum.
With binding sites exposed, cycling heads generate relative filament sliding. ATP is required for ongoing cycles, so 'ATP simply makes actin shorten' is not a mechanism. I-band/H-zone changes do not require the A-band filament length to shrink.
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Acetylcholine at the neuromuscular junction triggers muscle-membrane excitation that spreads along T-tubules.
Excitation leads to calcium release from the sarcoplasmic reticulum.
Calcium binds troponin and shifts tropomyosin to expose actin binding sites.
Myosin cross-bridge cycles require ATP, including detachment and re-cocking, and pull actin relative to myosin.
Actin and myosin filaments retain their lengths while their overlap changes and the sarcomere shortens.
Examiner tip
These are original indicative marking points, not an official Cambridge answer key. State assumptions and connect each conclusion to the supplied evidence.
