One question at a time
Original practice, your own questions and saved mark schemes. Official past papers are linked separately, never relabelled.
Moving against the gradient
Explain how sodium ions can be transported into a cell against their concentration gradient.
Original practice mark scheme
1 mark: sodium ions move from a lower to a higher concentration, against their concentration gradient. 1 mark: a specific carrier protein or pump in the membrane is involved. 1 mark: energy from ATP hydrolysis changes the conformation of the carrier protein/pump. Accept scientifically valid equivalent wording. No error-carried-forward marks.
Enzymes and temperature
Explain why the rate of an enzyme-controlled reaction falls rapidly above the optimum temperature.
Original practice mark scheme
1 mark: high temperature disrupts bonds maintaining tertiary structure. 1 mark: the active site changes shape and is no longer complementary to the substrate. 1 mark: fewer enzyme–substrate complexes form, so the rate decreases. Do not credit enzymes being killed.
Light and ATP
Describe the role of light in producing ATP during the light-dependent reaction of photosynthesis.
Original practice mark scheme
1 mark: light excites electrons in chlorophyll. 1 mark: electrons pass along electron carriers and energy is released. 1 mark: energy is used to pump protons across the thylakoid membrane, creating an electrochemical gradient. 1 mark: protons flow through ATP synthase, driving ATP formation from ADP and inorganic phosphate.
A measured amount
Calculate the amount, in mol, of sodium chloride in 5.85 g of NaCl. Use Mr(NaCl) = 58.5. Show your working.
Original practice mark scheme
M1: uses n = m / Mr and substitutes 5.85 / 58.5. A1: 0.100 mol. A1 depends on a valid method; do not award full marks for an unsupported final answer. No error-carried-forward rule.
A changing equilibrium
For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), explain the effect of increasing pressure at constant temperature on equilibrium yield.
Original practice mark scheme
1 mark: equilibrium shifts to the side with fewer moles of gas. 1 mark: there are 4 moles on the reactant side and 2 on the product side. 1 mark: equilibrium shifts right and the ammonia yield increases. Do not credit a change in Kc at constant temperature.
A resilient pH
Explain how a mixture of ethanoic acid and sodium ethanoate resists a decrease in pH when a small amount of strong acid is added.
Original practice mark scheme
1 mark: ethanoate ions are present from dissociation of sodium ethanoate. 1 mark: added H⁺ reacts with CH₃COO⁻ to form CH₃COOH. 1 mark: most added H⁺ is removed, so the H⁺ concentration and pH change only slightly.
Find the gradient
Given y = 3x³ − 2x² + 4, find dy/dx and the gradient of the curve at x = 2. Show your working.
Original practice mark scheme
M1: applies the power rule to both polynomial terms. A1: dy/dx = 9x² − 4x. A1: substitutes x = 2 to obtain 28. The final accuracy mark requires the correct derivative; no error-carried-forward marks.
Area under a curve
Evaluate the integral from 0 to 2 of (3x² + 2x) dx. Show your working.
Original practice mark scheme
M1: integrates the terms using the power rule. A1: antiderivative x³ + x². A1: evaluates [x³ + x²] from 0 to 2 and obtains 12. Final mark requires correct antiderivative and limit substitution.
Dependent or independent?
Events A and B satisfy P(A) = 0.4, P(B) = 0.5 and P(A ∩ B) = 0.2. Determine whether A and B are independent, showing your reasoning.
Original practice mark scheme
M1: calculates P(A)P(B) = 0.4 × 0.5 = 0.2. A1: states this equals P(A ∩ B), so the events are independent.
Two stores, two differences
Outline two differences between short-term memory and long-term memory in the multi-store model.
Original practice mark scheme
Award up to 2 marks for each of two differences (maximum 4). Difference 1 may concern capacity: STM is limited; LTM is potentially unlimited (2). Difference 2 may concern duration: STM lasts about 18–30 seconds without rehearsal; LTM can last a lifetime (2). An alternative valid difference is coding: STM predominantly acoustic, LTM predominantly semantic (2). Award only two distinct comparisons; no extra marks for a third.
Why conform?
Explain the difference between normative social influence and informational social influence.
Original practice mark scheme
1 mark: normative social influence involves a desire to be liked or accepted by a group. 1 mark: it typically leads to compliance without private acceptance. 1 mark: informational social influence involves a desire to be correct, especially in an ambiguous situation. 1 mark: it may lead to internalisation/private acceptance.
A stronger investigation
Explain one strength and one limitation of using a laboratory experiment to investigate memory.
Original practice mark scheme
Up to 2 marks for strength: control of extraneous variables (1) supports causal inference about the independent variable (1). Up to 2 marks for limitation: artificial setting or task (1) may reduce ecological validity/generalisation to everyday memory (1). Credit equivalent well-explained strength and limitation, applied to memory.