AQA AS Level Biology Paper 1, June 2024: Question 6
8 marks · Medium difficulty · Short Answer
Give two roles of phosphate ions, describe the effect of increased hydrogen ion concentration on plasma proteins, use a bar chart (Figure 7) to describe ion concentration patterns, and explain sodium ion transport mechanisms across cell membranes.
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Question text
06.1 Give two roles of phosphate ions in cells.
[2 marks]
06.2 Diseased lungs can cause carbon dioxide to build up in the blood plasma. This leads
to an increase in hydrogen ion concentration in the plasma.
Describe the effect this increase in hydrogen ion concentration has on the plasma
and on the proteins in the plasma.
Do not refer to the Bohr effect.
[2 marks]
Scientists measured the concentration of inorganic ions in the cytoplasm of
mammalian cells and in the tissue fluid surrounding those cells.
Figure 7 shows their results.
Figure 7
06.3 Use Figure 7 to describe two patterns shown in the total concentrations of positively
and negatively charged ions in the cytoplasm and in tissue fluid.
[2 marks]
06.4 In these mammalian cells, the:
• cell-surface membrane is permeable to sodium ions
• sodium ion concentration does not increase in the cytoplasm over time.
Use this information and Figure 7 to suggest and explain the ion transport
mechanisms involved in the transport of sodium ions.
[2 marks]
Mark scheme
Show the mark scheme
Question Marking Guidance Mark Comments
1. (In) DNA; 1. and 2. If neither
DNA or RNA named
2. (In) RNA;
allow 1 mark for
3. (In) ATP/ADP; nucleotide/nucleic
4. Phosphorylation; acid/phosphodiester
bond/sugar-
5. (In) phospholipids; phosphate backbone
2 max 1, 2 and 3. Accept any
06.1 (2 x other correct
AO1) biological compound
containing phosphate;
eg (in)RuBP or GP or
triose phosphate or
NAD
4. Accept binds with
substance to make it
more reactive
1. Increased (plasma) acidity
OR
Decreased (plasma) pH;
2. Denatures (protein) 2. Accept description
2 of bond changes, eg
OR
06.2 (2 x ‘disrupts hydrogen/
Changes (protein) tertiary structure AO1) ionic bonds’ for
OR ‘changes in tertiary
structure’
Changes active site (shape)
OR
Changes antigen-binding site (shape);
1. Equal positive and negative (in both); Accept answers in
either order
2. Higher (ion concentration) in cytoplasm;
Ignore reference to
sodium ions
06.3 (2 x
1. Accept no overall
AO2)
charge or no net
charge
2. Ignore more ions in
cytoplasm
1. (Sodium) ions move in (to cells) by facilitated 1. Accept a
diffusion down a concentration gradient; description of the
concentration
gradient, eg from high
2. (Sodium) ions move out (of cells) by active
(concentration) to low
transport against a concentration gradient;
2 (concentration)
06.4 (2 x
AO2) 2. Accept a
description of
transport against a
gradient, eg from low
(concentration) to high
(concentration)
How to answer it
Inorganic Ions & Transport Study Guide
What this question tests
This question assesses your knowledge of the biological roles of inorganic ions (specifically phosphates), the physiological impacts of pH changes on protein structure, chart interpretation skills (data analysis), and the application of membrane transport mechanisms (facilitated diffusion and active transport) to biological contexts.
Roles of Phosphate Ions in Cells
Give two roles of phosphate ions in cells. (2 marks)
✅ Correct Answers (Any 2)
- Component of DNA / RNA / nucleotides
- Component of ATP / ADP
- Used in phosphorylation of other molecules (making them more reactive)
- Component of phospholipids in cell membranes
💡 Key Knowledge
Phosphate ions PO₄³⁻ are incredibly versatile molecules in biochemistry. Memorise their exact locations: nucleic acids (sugar-phosphate backbone), energy currency (ATP), and membranes (phospholipid bilayer).
❌ Common Errors
Writing vague terms like "used in bones" (too mammalian-anatomical rather than cellular) or simply stating "energy" without linking it directly to nucleotides or ATP.
Effect of Hydrogen Ions on Plasma Proteins
Describe the effect this increase in hydrogen ion concentration has on the plasma and on the proteins in the plasma. (2 marks)
✅ Correct Answers
Mark 1 (Plasma): Increased plasma acidity OR decreased plasma pH.
Mark 2 (Proteins): Denatures protein OR changes protein tertiary structure / changes active site / changes ionic or hydrogen bonds.
🧠 Exam Technique
Note the negative constraint: "Do not refer to the Bohr effect." Examiners explicitly penalise answers that drift into haemoglobin oxygen-affinity explanations. Stick rigidly to general protein denaturation chemistry!
❌ Common Errors
Saying proteins are "killed" instead of denatured. Remember, macromolecules cannot be killed because they are not alive. Always use precise biochemical terminology like tertiary structure disruption.
Interpreting Ion Concentration Charts
Use Figure 7 to describe two patterns shown in the total concentrations of positively and negatively charged ions in the cytoplasm and in tissue fluid. (2 marks)
✅ Correct Answers (Any 2 patterns)
- Equal positive and negative ion concentrations in both cytoplasm and tissue fluid (electrochemical neutrality).
- Higher total ion concentration inside the cytoplasm compared to the tissue fluid.
🧠 Exam Technique
Read graph axes carefully. The total height of the bars represents total ion concentrations. Visually combine the white section ("other positive") and striped section ("sodium") to gauge total positive ions, and compare it directly to the grey bar ("negative ions").
❌ Common Errors
Focusing exclusively on sodium ions when the question specifically asks for total concentrations of positively and negatively charged ions.
Sodium Transport Mechanisms
Use this information and Figure 7 to suggest and explain the ion transport mechanisms involved in the transport of sodium ions. (2 marks)
✅ Correct Answers
1. Movement In: Sodium ions move in (to cells) by facilitated diffusion down a concentration gradient.
2. Movement Out: Sodium ions move out (of cells) by active transport against a concentration gradient.
💡 Key Knowledge
Look at Figure 7: Sodium ion concentration (striped bars) is clearly lower inside the cytoplasm than in the tissue fluid. Therefore, to enter the cell they go down their gradient (facilitated diffusion), but to maintain stable cytoplasmic concentrations over time without building up, they must be pumped back out against their gradient using ATP (active transport).
🧠 Exam Technique
To score both marks, you must include both the mechanism name (facilitated diffusion / active transport) and the direction relative to the concentration gradient ("down" vs "against/up").
Topics
Biology · 3.1 Biological molecules · 3.2 Cells
Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.