This free quiz has 12 real AQA A-level Biology exam questions on photosynthesis (26 marks, about 35 minutes). It marks itself: the tick-box question is marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.5.1)
the chemicals needed for the light-dependent reaction
where rubisco is found in a cell
what happens during photoionisation
why heat stress and lower rubisco activity slow the light-independent reaction
separating leaf pigments by paper chromatography, and calculating an Rf value
why leaves have different coloured pigments, and how light absorbed and colour relate to the rate of photosynthesis
using DCPIP and isolated chloroplasts to investigate the light-dependent reaction
describing the light-independent reaction (6 marks)
How to use it
Write each answer in full before you open the mark scheme. For the light-independent reaction, set it out as a sequence of steps and name every molecule in full, including glycerate 3-phosphate and triose phosphate. For the chromatography method, give practical steps, such as where the solvent level goes and when to remove the paper, rather than the theory.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Photoionisation is not photolysis. Some students described only photolysis and scored nothing. Answers that mentioned only chloroplasts or photosystems missed a mark, and few said that chlorophyll becomes positively charged.
✔ Gains credit: chlorophyll absorbs light, which excites electrons; the electrons are lost (to the electron transport chain), so the chlorophyll becomes positively charged.
What reduces DCPIP. Common misconceptions were that DCPIP is reduced by protons or by reduced NADP. Many answers just called a tube without chloroplasts “a control” without saying what it shows.
✔ Gains credit: DCPIP is reduced by electrons from chlorophyll in the light-dependent reaction; a control shows that light alone does not change DCPIP and that chloroplasts are needed.
Explain what rubisco does. One in four students scored zero, mostly by only describing rubisco denaturing. Others left out RuBP or carbon dioxide, gave a six-carbon product without mentioning GP, or confused the Calvin cycle with the Krebs cycle.
✔ Gains credit: rubisco catalyses the reaction of carbon dioxide with RuBP, producing two molecules of GP.
Roles of ATP and reduced NADP. Students wrote reduced NAD instead of reduced NADP, said ATP provides phosphate, or said that GP is oxidised to triose phosphate. In one question almost 50% scored zero because they didn't name ATP or reduced NADP at all.
✔ Gains credit: ATP provides the energy and reduced NADP reduces GP to triose phosphate in the light-independent reaction.
Name GP and triose phosphate correctly. Some students called GP “glucose phosphate” and lost the mark. Writing only “TP” was penalised, because it is not an abbreviation used in the specification.
✔ Gains credit: glycerate 3-phosphate (GP) and triose phosphate written in full; triose phosphate is used to regenerate RuBP or is converted to hexose or another named organic substance.
Chromatography method details. Many answers only said to put the paper in solvent, add a lid and leave it for a set time. Weaker answers mixed up the chlorophyll solution and the solvent, or used water.
✔ Gains credit: draw a pencil line as the origin, add the pigment solution to it, keep the level of an organic solvent below the line, and remove the paper before the solvent reaches the top (or mark the solvent front).
Solubility in the solvent. 61% of students scored zero when explaining why two solvents separated different numbers of pigments. Many said one solvent was “stronger” or “more concentrated”, or that the pigments had different wavelengths.
✔ Gains credit: pigments have different solubilities in different solvents (or different affinities or polarities); referring to solubility in a “solution” rather than a solvent gained only one mark.
Keep practising
The other AQA 3.5 self-marking quizzes: Respiration · Energy and ecosystems · Nutrient cycles
Next, topic 3.6: the stimuli and receptors quiz
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Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.