This free quiz has 10 real AQA A-level Biology exam questions on lipids (22 marks, about 30 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 3.1.3)
saturated and unsaturated fatty acids
the carboxyl group of a fatty acid
how triglycerides and phospholipids differ in structure
how ester bonds form in condensation reactions
the emulsion test for lipids
why phospholipids form a bilayer and triglycerides don't
using data on fatty acids to explain membrane fluidity
comparing the structure and properties of triglycerides and phospholipids (5 marks)
How to use it
Write each answer in full before you open the mark scheme, then tick only the points you really made. For the comparison question, write each point as a matched pair (triglyceride … whereas phospholipid …), because separate descriptions don't score.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Glycerol, not “glyceride”. Many students wrote “glyceride” instead of glycerol, or left glycerol out of a phospholipid altogether. Separate descriptions of the two lipids weren't credited as a comparison.
✔ Gains credit: both contain glycerol joined to fatty acids, but a triglyceride has three fatty acids while a phospholipid has two fatty acids and a phosphate group.
Ester bonds. “Glycosidic” was a common wrong name for the bond between glycerol and a fatty acid, and some thought phospholipids contain phosphodiester bonds.
✔ Gains credit: an ester bond forms between glycerol and a fatty acid.
Condensation removes water. Some described triglyceride formation without saying three water molecules are lost, or removed an H from the wrong part of glycerol.
✔ Gains credit: condensation reactions between one glycerol and three fatty acids remove three molecules of water, using the OH of the fatty acid and the H of an OH group on glycerol.
Emulsion test steps. Fewer than half of students gained both marks. Errors included adding water before ethanol, heating the sample, and calling the result “cloudy” or a “precipitate”.
✔ Gains credit: shake the sample with ethanol, then add water; a white or milky emulsion shows lipid is present.
C=C double bonds. Students often said an unsaturated fatty acid has a double bond without saying it is between two carbon atoms.
✔ Gains credit: an unsaturated fatty acid has a double bond between carbon atoms (C=C).
Saturation and melting point. Good answers lost the mark by writing about hydrogen “molecules” rather than atoms, or about boiling point instead of melting point.
✔ Gains credit: as the number of C=C double bonds increases, the melting point decreases.
Hydrophilic and hydrophobic. Fewer students stated that a triglyceride is only hydrophobic. Some called the phosphate group hydrophobic or a “phosphorus group”.
✔ Gains credit: the phosphate group of a phospholipid is hydrophilic and attracts water, while triglycerides are only hydrophobic (non-polar).
Keep practising
The other AQA 3.1 self-marking quizzes: Carbohydrates · 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.