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AQA A-Level Biology (Paper 1) Smart practice A mixed round aimed at your weak spots
Unit 1
Biological molecules
Monomers and polymers; carbohydrates
Monomers, polymers and carbohydrates
0%
Lipids
Lipids
0%
Proteins
General properties of proteins
0%
Many proteins are enzymes
0%
Nucleic acids are important information-carrying molecules
Structure of DNA and RNA
0%
DNA replication
0%
ATP
ATP
0%
Water; inorganic ions
Water and inorganic ions
0%
Unit 2
Cells
Cell structure
Structure of eukaryotic cells
0%
Structure of prokaryotic cells and of viruses
0%
Methods of studying cells
0%
All cells arise from other cells
All cells arise from other cells
0%
Transport across cell membranes
Membrane structure, diffusion and osmosis
0%
Active transport and co-transport
0%
Cell recognition and the immune system
Antigens, phagocytosis and T lymphocytes
0%
B lymphocytes, antibodies and vaccination
0%
HIV, monoclonal antibodies and the ELISA test
0%
Unit 3
Organisms exchange substances with their environment
Surface area to volume ratio
Surface area to volume ratio
0%
Gas exchange
Adaptations of gas exchange surfaces
0%
Human gas exchange, ventilation and lung disease
0%
Digestion and absorption
Digestion and absorption
0%
Mass transport in animals
Haemoglobin and the transport of oxygen
0%
The heart, cardiac cycle and cardiovascular disease
0%
Blood vessels and tissue fluid
0%
Mass transport in plants
Xylem and the cohesion-tension theory
0%
Phloem and translocation by mass flow
0%
Unit 4
Genetic information, variation and relationships between organisms
DNA, genes and chromosomes
DNA, genes and chromosomes
0%
DNA and protein synthesis
Genome, proteome, transcription and splicing
0%
Translation: ribosomes, tRNA and ATP
0%
Genetic diversity can arise as a result of mutation or during meiosis
Gene mutations and chromosome non-disjunction
0%
Meiosis and genetic variation
0%
Genetic diversity and adaptation
Genetic diversity and adaptation
0%
Species and taxonomy
Species and taxonomy
0%
Biodiversity within a community
Biodiversity within a community
0%
Investigating diversity
Investigating diversity
0%
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Digestion and absorption

Practise 19 exam-style questions on Digestion and absorption for AQA A-Level Biology (Paper 1). Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with the Study Helper on hand if you get stuck.

  • 19 questions
  • 1–8 marks each
  • Instant marking
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19 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

Disaccharidases such as maltase are bound to the cell-surface membranes of the epithelial cells lining the ileum, rather than being released into the lumen.

Suggest two advantages of this.

Model answer

1. Glucose is produced right next to the co-transport proteins in the membrane, so it can be absorbed quickly.
2. The enzymes stay in place and are not carried away with the gut contents, so they can be used again and again.

Explanation

Membrane-bound disaccharidases and dipeptidases carry out the final stage of digestion at the surface of the epithelial cells, on the microvilli. Producing monosaccharides exactly where the co-transport proteins are keeps their concentration high at the membrane, which speeds up absorption. Enzymes free in the lumen would move on with the food and be lost.

Mark scheme
  1. 1 mark

    Monosaccharides / glucose are produced next to the (co-transport / carrier) proteins that absorb them, so they are absorbed quickly / their concentration stays high at the cell surface

    List rule: if more than two advantages are given, each wrong or contradictory extra answer cancels one correct answer. Accept 'glucose does not have to diffuse through the lumen to reach the cells' or 'maintains a (high) concentration / concentration gradient of glucose for absorption'.

  2. 1 mark

    The enzymes are not lost / carried away with the contents of the gut, so they can be used again

    Accept 'the enzymes are not egested'. Insufficient: 'the enzymes are held in place' with no advantage.

Question 2

3 marks

The diagram shows a polypeptide and a dipeptide in the human gut. Arrows J, K and L point to peptide bonds.

Name the type of enzyme that hydrolyses bond J, bond K and bond L during digestion.

A chain of ten circles joined by short lines, labelled 'Polypeptide', with H₂N at the left end and COOH at the right end. Arrow J points to the line between the fifth and sixth circles, in the middle of the chain. Arrow K points to the line between the ninth and tenth circles, at the COOH end of the chain. Below, two circles joined by a line are labelled 'Dipeptide', and arrow L points to the line joining them. A key shows that a circle is an amino acid and a line is a peptide bond.

Model answer

J: endopeptidase
K: exopeptidase
L: dipeptidase (membrane-bound)

Explanation

Endopeptidases hydrolyse peptide bonds within a polypeptide chain, producing shorter peptides. Exopeptidases hydrolyse the peptide bonds at the ends of a chain, removing terminal amino acids. Membrane-bound dipeptidases on the epithelial cells of the ileum hydrolyse the bond between the two amino acids of a dipeptide. The prefixes help: endo- means within and exo- means outside.

Mark scheme
  1. 1 mark

    J - endopeptidase

    1 mark for each bond (points 1 to 3). Accept phonetic spellings. Accept a correctly named endopeptidase (pepsin, trypsin or chymotrypsin) for J.

  2. 1 mark

    K - exopeptidase

    Reject endopeptidase for K. Accept carboxypeptidase for K.

  3. 1 mark

    L - (membrane-bound) dipeptidase

    Reject exopeptidase or endopeptidase for L.

Question 3

4 marks

The flow chart shows the digestion of starch in the human gut.

Name substance X.

Name the enzyme that catalyses step 1 and the enzyme that catalyses step 2.

Give the precise location of the enzyme that catalyses step 2.

Flow chart of 3 boxes joined by arrows, read from left to right. The first box is "Starch", which leads (along an arrow labelled "step 1") to box X, which leads (along an arrow labelled "step 2") to "Glucose".

Model answer

X is maltose.
Step 1 is catalysed by amylase.
Step 2 is catalysed by maltase (a disaccharidase).
Maltase is bound to the cell-surface membranes of the epithelial cells lining the ileum.

Explanation

Amylase, from the salivary glands and the pancreas, hydrolyses glycosidic bonds in starch to produce maltose. Maltase is a membrane-bound disaccharidase on the microvilli of the epithelial cells of the ileum; it hydrolyses maltose to glucose, which is then absorbed by co-transport. Take care with spelling: maltose is the sugar and maltase the enzyme. A common error is to describe starch being digested straight to glucose in one step.

Mark scheme
  1. 1 mark

    (X =) maltose

    Reject maltase for X.

  2. 1 mark

    (Step 1 =) amylase

    Accept salivary amylase or pancreatic amylase. Insufficient: 'carbohydrase' alone.

  3. 1 mark

    (Step 2 =) maltase / disaccharidase

    Reject maltose for the enzyme. Reject amylase or sucrase.

  4. 1 mark

    Bound to the cell-surface membranes (of the microvilli) of the epithelial cells lining the ileum

    Accept 'membrane-bound, on the epithelial cells of the small intestine'. Insufficient: 'small intestine' or 'ileum' alone.

Question 4

6 marks

Describe how lipids in food are digested in the small intestine and how the products of their digestion enter the epithelial cells lining the ileum.

Do not include what happens to the products after they enter the epithelial cells.

Model answer

In the small intestine, bile salts emulsify the lipids into small droplets, which greatly increases their surface area. Lipase then hydrolyses the ester bonds in the triglycerides, producing monoglycerides and fatty acids. Bile salts combine with these monoglycerides and fatty acids to form tiny micelles, which keep them in solution and carry them to the surface of the epithelial cells, keeping their concentration high next to the cells. There the monoglycerides and fatty acids are released and, because they are lipid-soluble, they diffuse across the phospholipid bilayer of the cell-surface membrane into the cells.

Explanation

Bile salts have two separate roles: emulsification, which increases the surface area for lipase, and micelle formation, which carries the products of digestion to the epithelium. Lipase hydrolyses ester bonds to give monoglycerides and fatty acids, which cross the membrane by simple diffusion because they are lipid-soluble. Common errors are to say that emulsification forms micelles or is a hydrolysis reaction, that micelles themselves cross the membrane, or that the products enter by facilitated diffusion or co-transport.

Mark scheme
  1. 1 mark

    Bile salts emulsify lipids into (small) droplets

    Max 6. Reject 'bile salts digest / hydrolyse lipids'.

  2. 1 mark

    This increases the surface area (for lipase)

    Accept 'more lipid exposed to lipase'.

  3. 1 mark

    Lipase hydrolyses ester bonds (in triglycerides)

    Reject 'peptide' or 'glycosidic bonds'.

  4. 1 mark

    Producing monoglycerides and fatty acids

    Accept glycerol for monoglycerides.

  5. 1 mark

    Bile salts combine with monoglycerides and fatty acids to form micelles

    Reject 'micelles are formed by emulsification'.

  6. 1 mark

    Micelles make the monoglycerides / fatty acids (more) soluble in water / carry them (through the watery contents of the lumen) to the epithelial cells

    Accept 'bring / transport them to the lining of the ileum'. For monoglycerides / fatty acids accept glycerol; ignore 'lipids' or 'triglycerides'.

  7. 1 mark

    Micelles release them at the cell-surface membrane / maintain a high concentration of monoglycerides / fatty acids next to the epithelial cells

    Accept 'keep up a concentration gradient into the cells'.

  8. 1 mark

    Monoglycerides and fatty acids diffuse across the phospholipid bilayer (because they are lipid-soluble / non-polar)

    Reject 'facilitated diffusion' or 'co-transport'. Ignore 'micelles are absorbed'; the mark needs monoglycerides or fatty acids diffusing.

Ready to try the rest? Every answer you write is marked against the mark scheme, so you can see exactly where the marks are.

Study Helper Hints first, answers after you try

Stuck on this one? Ask for a hint and I’ll point you in the right direction, without giving the answer away. Once you’ve checked your answer, I’ll show you how the marks are awarded.