This free quiz has 11 real AQA A-level Biology exam questions on carbohydrates (26 marks, about 35 minutes). It marks itself: tick-box, table and graph questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.1.2)
the bonds that hold cellulose molecules together
biochemical tests for starch and reducing sugars
which elements are found in carbohydrates and other biological molecules
matching diagrams of biological molecules to their descriptions
differences between cellulose and glycogen
why starch and glycogen are good storage molecules
measuring reducing sugar, and reading a rate from a graph of starch hydrolysis
how the structures of starch and cellulose relate to their functions
How to use it
Write each written answer in full before you open the mark scheme. Be strict when you tick marking points: the examiner needs the same idea, in the right words. For the graph question, draw your tangent on paper and show your working.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Starch is compact because it's helical. Many students said starch is compact but didn't link this to its coiled or helical shape. Fewer linked branching to the faster release of glucose for respiration.
✔ Gains credit: starch is coiled/helical so compact, insoluble so it doesn't affect water potential, and branched so glucose is readily released by hydrolysis.
Cellulose fibrils. Some students confused microfibrils with myofibrils from muscle, or didn't link the structure of cellulose to its strength.
✔ Gains credit: long, straight, unbranched chains of β-glucose that form microfibrils, which provide strength and rigidity.
Water is lost in condensation. Many students said water is lost when monosaccharides join but didn't take it away when working out the formula of the product.
✔ Gains credit: monosaccharides are joined by a condensation reaction forming a glycosidic bond, removing one H₂O per bond, so two C₆H₁₂O₆ give C₁₂H₂₂O₁₁.
Hydrolysed, not “broken down”. The most common reason for losing marks was writing “broken down” instead of hydrolysed. Some called maltose a polysaccharide or a monosaccharide.
✔ Gains credit: maltose is a disaccharide that must be hydrolysed into glucose, breaking the glycosidic bond.
Benedict's test. Some students left out the heating step, wrote only “use a water bath”, or mixed in the acid step from the non-reducing sugar test.
✔ Gains credit: heat with Benedict's solution; a red precipitate (or green, yellow, orange or brown) shows a reducing sugar.
Non-reducing sugar steps. Few students wrote the practical steps clearly and in the right order.
✔ Gains credit: heat with acid (e.g. HCl), neutralise with an alkali (e.g. NaHCO₃), then heat with Benedict's solution to give a red precipitate.
Make comparisons explicit. Students who gave only one side of a difference, or described two molecules separately, gained no marks.
✔ Gains credit: a linked comparison, e.g. starch contains α-glucose and is branched, whereas cellulose contains β-glucose and is unbranched.
Keep practising
The other AQA 3.1 self-marking quizzes: Lipids · Proteins · Enzymes · Nucleic acids · ATP, water and ions
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.