This free quiz has 12 real AQA A-level Biology exam questions on digestion and absorption (28 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 3.3.3)
how fatty acids and glycerol enter intestinal epithelial cells
what digestion is
the peptidases needed for the complete hydrolysis of proteins
why endopeptidases and exopeptidases together speed up protein digestion
the hydrolysis of triglycerides, and explaining data on lipid digestion
the functions of bile salts, emulsification and micelles (4 marks)
the complete digestion of starch (4 marks)
how amino acids are absorbed in the ileum (4 marks)
How to use it
Write each written answer in full before you open the mark scheme. Always say hydrolysis, name the bond that is broken, and give each enzyme with its substrate and product. Keep digestion and absorption apart, and answer only the process the question asks about.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
What digestion means. Many definitions were too general, such as “food is broken down ready for absorption”, and many students thought absorption is part of digestion.
✔ Gains credit: digestion is the hydrolysis of large, insoluble substances into smaller, soluble substances (polymers to monomers).
Name the bond hydrolysed. Some wrote about breaking hydrogen bonds or glycosidic bonds when triglycerides are digested. Others said enzymes hydrolyse amino acids rather than the bonds between them, and “dipeptide bond” or “polypeptide bond” was rejected.
✔ Gains credit: hydrolysis breaks bonds by adding water: peptide bonds in proteins, glycosidic bonds in starch and ester bonds in triglycerides.
Three types of peptidase. Only about 50% of students named dipeptidases, and the most common wrong answer was protease. Many confused the roles of endopeptidases and exopeptidases, or invented names such as “exodipeptidase”.
✔ Gains credit: endopeptidases hydrolyse internal peptide bonds, exopeptidases hydrolyse terminal peptide bonds, and membrane-bound dipeptidases hydrolyse dipeptides into amino acids.
Endopeptidases make more ends. Only one in five students gained both marks when explaining why the two enzymes work faster together. Most described what each enzyme does but stopped there.
✔ Gains credit: endopeptidases produce shorter polypeptides with more ends, giving more surface area for exopeptidases to act on.
Starch digestion in two steps. Some described starch going straight to glucose in one step, or wrote “disaccharide” instead of maltose. Few mentioned membrane-bound enzymes, and answers about “breakdown” and “sugar” stayed at GCSE level.
✔ Gains credit: amylase hydrolyses glycosidic bonds in starch to give maltose, then a membrane-bound maltase (disaccharidase) hydrolyses maltose to glucose.
Bile salts don't digest fats. Some thought bile salts digest fats or emulsify them into fatty acids and glycerol. Saying emulsification makes digestion “easier”, or that lipase simply “digests” lipid, wasn't credited.
✔ Gains credit: bile salts emulsify lipids into small droplets, which increases the surface area for faster hydrolysis by lipase.
Micelles aren't emulsification. There was much confusion between micelles and emulsification, and many thought micelles form by emulsification. Saying micelles increase surface area was rejected, and some answers referred only to the lumen, not the cells.
✔ Gains credit: micelles contain bile salts and fatty acids or monoglycerides, make them more soluble and carry them to the cells lining the ileum, keeping a higher concentration there.
Keep practising
The other AQA 3.3 self-marking quizzes: Surface area to volume · Gas exchange · Mass transport in animals · Mass transport in plants
Topic 3.2 quizzes start with cell structure
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.