AQA AS Level Biology Paper 1, June 2022: Question 1

8 marks · Medium difficulty · Short Answer

Identify biological molecules from given structural formulas and describe the mechanism of absorption of amino acids in the ileum.

Practise this question

Question

Figure 1 shows chemical structures labelled A to E. A shows a disaccharide structure, B shows a triglyceride with three RCOO groups attached to a glycerol box, C shows a short nucleic acid strand containing thymine and cytosine, D shows another disaccharide structure, and E shows a dipeptide formed from two amino acids. Below this, Table 1 requires letters A to E to be matched with statements about hydrolysis in the ileum, formation by condensation of alpha-glucose, formation by DNA polymerase, and a positive emulsion test. Question 01.2 asks to describe the mechanism for the absorption of amino acids in the ileum with answer lines.
Question text

01.1 Figure 1 shows the structure of some biological molecules.

Figure 1

Complete Table 1 by writing the correct letter, A, B, C, D or E, in the box next to each

statement. Each letter may be used once, more than once, or not at all.

[4 marks]

Table 1

Letter Statement

is hydrolysed in the ileum and a product of this hydrolysis is found in

micelles

is formed by a condensation reaction between two α-glucose

molecules

is formed by the action of DNA polymerase

gives a positive result in an emulsion test

01.2 Describe the mechanism for the absorption of amino acids in the ileum.

[4 marks]

Mark scheme

Show the mark scheme The mark scheme gives answers for question 01.1 as B, A, C, B for 4 marks. For question 01.2, it awards up to 4 marks for points including facilitated diffusion of amino acids, co-transport with sodium ions, active transport of sodium ions out of cells, creating a concentration gradient, and facilitated diffusion into the blood.

Question Marking Guidance Mark Comments

01.1 B: is hydrolysed in the ileum and a product of

this hydrolysis is found in micelles;

A: is formed by a condensation reaction 4

between two α-glucose molecules; (4 x AO1)

C: is formed by the action of DNA polymerase;

B: gives a positive result in an emulsion test;

1. and 5. Accept

01.2 1. Facilitated diffusion of amino acid (into cell

diffusion via

when higher concentration in lumen);

channel/carrier

2. Co-transport; proteins for ‘facilitated

3. Sodium ions actively transported from cell to diffusion’

blood/capillary/tissue fluid;

3. Accept ‘pumped’ for

4. Creating sodium ion concentration/diffusion 4 max

transported

gradient; (4 x AO1)

3. and 4. Accept Na+

5. Facilitated diffusion of amino acid into

blood/capillary; for sodium ion(s)

3. and 4. Max 1 if ions

not mentioned

How to answer it

Biological Molecules and Absorption Study Guide

What this question tests

This question assesses your ability to recognise the chemical structures of key biological molecules (triglycerides, disaccharides, nucleotides, and amino acids), understand biochemical tests, recall DNA replication enzymes, and explain transport mechanisms across cell membranes in the ileum (co-transport).

Question 01.1 (4 Marks)

Identifying Biological Molecules from Structure and Function

✅ Correct Answers

  • B — is hydrolysed in the ileum and a product of this hydrolysis is found in micelles
  • A — is formed by a condensation reaction between two alpha-glucose molecules
  • C — is formed by the action of DNA polymerase
  • B — gives a positive result in an emulsion test

💡 Key Knowledge

  • Molecule A: A disaccharide (maltose) formed via 1,4 glycosidic bonds.
  • Molecule B: A triglyceride (glycerol + 3 fatty acids), which forms emulsions and yields monoglycerides/fatty acids packaged into micelles.
  • Molecule C: DNA polynucleotide chain showing phosphodiester bonding between nucleotides.
  • Molecule D: Another disaccharide isomer (such as cellobiose/beta-linkage representation).
  • Molecule E: A dipeptide formed by a condensation reaction between two amino acids (showing a peptide bond).

🧠 Exam Technique

Notice that letters can be used more than once (as seen with letter B appearing twice). Do not eliminate a letter just because you've already used it. Read each statement carefully against the structural properties shown in Figure 1.

❌ Common Errors

Confusing disaccharides (A) with triglycerides (B) or mixing up DNA polymerase function with RNA polymerase or DNA helicase. Ensure you link the emulsion test directly to lipids (triglycerides).

Mark breakdown: 4 marks total (1 mark for each correct table row match: B, A, C, B).
Question 01.2 (4 Marks max)

Mechanism of Amino Acid Absorption in the Ileum

✅ Marking Points (4 Max)

  • Point 1: Facilitated diffusion of amino acids into the epithelial cell (when concentration is higher in the lumen).
  • Point 2: Co-transport mechanism involved with sodium ions (Na⁺).
  • Point 3: Sodium ions are actively transported out of the cell into the blood/capillary/tissue fluid (via the sodium-potassium pump).
  • Point 4: This creates/maintains a sodium ion concentration and diffusion gradient between the lumen and the epithelial cell.
  • Point 5: Facilitated diffusion of amino acids from the epithelial cell into the blood/capillary.

💡 Key Knowledge: Co-transport

Amino acids, much like glucose, rely on an indirect active transport system. The active transport of Na⁺ sets up a steep electrochemical gradient. As Na⁺ moves down its concentration gradient back into the cell via a carrier protein, it drags an amino acid along with it against the amino acid's concentration gradient.

🧠 Exam Technique

When describing a physiological mechanism like absorption, write in a logical chronological sequence: start in the lumen, move into the epithelial cell, explain the active transport role of sodium ions, and finish at the capillary blood supply.

❌ Common Errors

Forgetting to explicitly mention ions when discussing gradients (Point 3 and 4 lose the mark if "ions" or "Na⁺" are omitted). Also, avoid stating that amino acids are actively transported directly by ATP—they move via co-transport driven by the sodium gradient.

Mark breakdown: Maximum of 4 marks awarded from the 5 available marking points. Clear sequential description and exact terminology (sodium ions, co-transport, active transport) are essential for top marks.

Topics

Biology · 3.1 Biological molecules · 3.3 Organisms exchange substances with their environment

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.