Monomers, Water and Inorganic Ions: AQA A Level Biology Exam Questions by Topic

AQAMonomers, Water and Inorganic IonsExam Questions
Written by Tom Whitburn

This page brings together three short sections of AQA 3.1: monomers and polymers (3.1.1), water (3.1.7) and inorganic ions (3.1.8). Each is small, but the ideas run through the whole course. You need to define monomers and polymers, describe condensation and hydrolysis reactions, explain the properties of water that matter in biology, and recognise the roles of hydrogen, iron, sodium and phosphate ions. They are examined as quick recall, as five-mark extended answers and as calculations set in a new context.

The examiners' reports show where the marks go. Students call monomers 'building blocks', write 'heat capacity' or 'latent heat of vaporisation' without saying high or large (only 32% gave three properties of water correctly), give physics definitions instead of what a property does for an organism, think water is produced in photosynthesis, and say more hydrogen ions raise the pH. The calculations are hard: only 16% simplified the iron ratio to x : 1 and only 12% got the hydrogen ion percentage right.

Start with monomers and polymers, then water, then inorganic ions, and finish with the two calculations. Answer each on paper before you open the mark scheme. If you'd like help with this topic, my AQA masterclasses run online on Tuesdays at 5.15pm for Year 12 and on Wednesdays or Thursdays at 6.30pm for Year 13.

What you need from GCSE

Each question on this page assumes you're secure on these GCSE ideas. If any of them feels shaky, look it up before you start.

  • GCSE: large molecules such as starch, proteins and lipids are broken down by enzymes into small, soluble molecules. See the Carbohydrates page for how this works in sugars.
  • GCSE: water moves up a plant in the xylem and evaporates from the leaves in transpiration; sweating cools us as the water evaporates.
  • GCSE: red blood cells contain haemoglobin, which carries oxygen from the lungs to the tissues.
  • GCSE: the pH scale: the lower the pH, the more acidic the solution. Enzymes and other proteins work best at an optimum pH. See the Enzymes page.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Monomer: a smaller unit from which larger molecules are made, such as a monosaccharide, an amino acid or a nucleotide. Not a 'building block'.
  • Polymer: a molecule made from a large number of monomers joined together.
  • Condensation reaction: joins two molecules with a chemical bond and eliminates a molecule of water.
  • Hydrolysis reaction: breaks a chemical bond between two molecules using a molecule of water.
  • Metabolite: a substance that takes part in metabolic reactions. Water is used in hydrolysis and photosynthesis and produced in condensation and respiration.
  • Solvent: a liquid that substances dissolve in. Metabolic reactions happen in solution in water, and dissolved substances are transported in it.
  • High heat capacity: water takes a lot of energy to change its temperature, so it buffers changes in temperature.
  • Large latent heat of vaporisation: a lot of energy is needed to evaporate water, so evaporation gives a cooling effect with little water lost.
  • Cohesion: water molecules stick together by hydrogen bonds between the molecules, supporting columns of water in xylem and producing surface tension.
  • Inorganic ion: a charged particle such as H⁺, Fe²⁺, Na⁺ or PO₄³⁻, found in solution in cytoplasm and body fluids.
  • Co-transport: sodium ions and glucose or amino acids moving into a cell together through one carrier protein, down the sodium concentration gradient set up by active transport.

What these questions cover (AQA 3.1.1, 3.1.7 and 3.1.8)

The questions test these statements from the AQA AS and A-level Biology specification (7401/7402):

  • Biochemical basis of life: The variety of life, both past and present, is extensive, but the biochemical basis of life is similar for all living things. (background to the whole of 3.1; not examined on its own)
  • Monomers: Monomers are the smaller units from which larger molecules are made.
  • Polymers: Polymers are molecules made from a large number of monomers joined together. (tested in Question 3, on polymers and their monomers)
  • Examples of monomers: Monosaccharides, amino acids and nucleotides are examples of monomers.
  • Condensation: A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.
  • Hydrolysis: A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.
  • Water: Water is a major component of cells. It has several properties that are important in biology. In particular, water:
  • Metabolite: is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
  • Solvent: is an important solvent in which metabolic reactions occur (tested in Question 10, on five properties of water)
  • Heat capacity: has a relatively high heat capacity, buffering changes in temperature
  • Latent heat of vaporisation: has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
  • Cohesion: has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.
  • Inorganic ions: Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations.
  • Specific roles: Each type of ion has a specific role, depending on its properties.
  • Students should be able to recognise the role of ions in the following topics: hydrogen ions and pH; iron ions as a component of haemoglobin; sodium ions in the co-transport of glucose and amino acids; and phosphate ions as components of DNA and of ATP.

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 17 questions are worth 44 marks, so about 57 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Monomers, polymers and the reactions that join them (3.1.1)

Question 1

AS Paper 1 · June 2018 · Q02.1 · 1 mark · Medium

Define a monomer.

Question text: what is a monomer? 1 mark.
Show the mark scheme Mark scheme: a smaller or repeating unit or molecule from which larger molecules or polymers are made. Reject atoms, elements and 'building blocks'.

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From the examiners' report: Almost 60% got this. Give both halves of the definition: a smaller unit, and what it makes. 'Building blocks' isn't accepted.

Question 2

AS Paper 1 · November 2020 · Q01.1 · 4 marks

Match four molecules to statements about monomers and polymers.

Figure 1: A alpha-glucose, B an amino acid, C ATP (adenine, ribose, three phosphates), D beta-glucose; Table 1 statements: a monomer in an enzyme's active site, a monomer in cellulose, produced in photosynthesis and respiration, forms a polymer giving a positive biuret test.
Show the mark scheme Mark scheme: B, D, C, B, in that order.

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From the examiners' report: Each letter can be used once, more than once or not at all, so don't rule out B just because you've used it. Cellulose is made of beta-glucose.

Question 3

A level Paper 1 · June 2019 · Q10.3 · 5 marks

Describe the reactions that convert polymers to monomers and back, with two named examples.

Question text: describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers; give two named examples of polymers and their monomers, 5 marks.
Show the mark scheme Mark scheme: condensation joins monomers, forms a chemical bond and releases water; hydrolysis breaks the bond and uses water; two examples of a polymer with its monomer; a correct bond in a named polymer. Reject triglycerides and ester bonds.

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From the examiners' report: There's no examiners' report for this paper, so this tip comes from the mark scheme. Say water is released in condensation and used in hydrolysis, pick true polymers (not triglycerides) and name the bond, such as glycosidic or peptide.

Question 4

AS Paper 2 · June 2016 · Q05.1 · 1 mark · Easy

Name the type of reaction that breaks down phospholipids to release phosphate.

Figure 6: mean mass of phosphate in cherry seed embryos rising at 5 °C but not at 25 °C over 16 weeks; question: name the reaction that breaks down phospholipids to release phosphate, 1 mark.
Show the mark scheme Mark scheme: hydrolysis.

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From the examiners' report: The vast majority got this. Common wrong answers were condensation and phosphorylation.

Question 5

A level Paper 1 · June 2017 · Q02.2 · 2 marks

Suggest how glycogen acts as a source of energy for an embryo.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question text: during early pregnancy glycogen in cells lining the uterus is an energy source for the embryo; suggest how glycogen acts as a source of energy, not including transport across membranes, 2 marks.
Show the mark scheme Mark scheme: hydrolysed to glucose; glucose used in respiration. 'Broken down' is ignored and 'energy produced' loses the second mark.

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From the examiners' report: There's no examiners' report for this paper, so this tip comes from the mark scheme. Name the reaction: 'hydrolysed', not 'broken down'. Then say the glucose is used in respiration, which releases energy rather than producing it.

Properties of water (3.1.7)

Question 6

AS Paper 1 · June 2017 · Q08.1 · 3 marks · Medium

Give three properties of water that are important in biology.

Question text: give three properties of water that are important in biology, 3 marks.
Show the mark scheme Mark scheme: any three of: a metabolite; a solvent; a relatively high heat capacity; a relatively large latent heat of vaporisation; cohesion or hydrogen bonds between molecules. 'Polar' alone isn't accepted.

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From the examiners' report: Only 32% got all three. Give properties, not reactions such as condensation, and say high heat capacity and large latent heat of vaporisation.

Question 7

AS Paper 2 · June 2016 · Q02.5 · 2 marks · Hard

Suggest two reasons why a plant's water uptake might not equal its rate of transpiration.

Question text: a student measured the rate of water uptake to compare transpiration in two plant species; suggest two reasons why the rate of water uptake might not be the same as the rate of transpiration, 2 marks.
Show the mark scheme Mark scheme: water used for support or turgidity; used in photosynthesis; used in hydrolysis; produced in respiration.

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From the examiners' report: Only a third scored. Water is used in photosynthesis and hydrolysis and produced in respiration; many got these the wrong way round or wrote about potometer leaks.

Question 8

AS Paper 1 · June 2018 · Q08.1 · 2 marks

State and explain the property of water that helps to buffer changes in temperature.

Question text: state and explain the property of water that can help to buffer changes in temperature, 2 marks.
Show the mark scheme Mark scheme: a relatively high (specific) heat capacity; it can gain or lose a lot of heat without changing temperature (due to hydrogen bonding between water molecules).

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From the examiners' report: Don't mix up heat capacity and latent heat of vaporisation, or hedge with 'latent heat capacity'. The hydrogen bonds are between water molecules.

Question 9

AS Paper 2 · June 2024 · Q01.1 · 2 marks

Describe why water's high heat capacity and large latent heat of vaporisation matter to organisms.

Question text: water has a high heat capacity and a large latent heat of vaporisation; describe the importance of each of these properties to living organisms, 2 marks.
Show the mark scheme Mark scheme: high heat capacity buffers changes in temperature; large latent heat of vaporisation provides a cooling effect through evaporation.

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From the examiners' report: Almost half got both. Say what each property does for the organism rather than giving the physics definition.

Question 10

AS Paper 2 · November 2021 · Q09.1 · 5 marks

Explain five properties that make water important for organisms.

Question text: explain five properties that make water important for organisms, 5 marks.
Show the mark scheme Mark scheme: metabolite in condensation, hydrolysis, photosynthesis or respiration; solvent so reactions occur or substances are transported; high heat capacity buffers temperature; large latent heat of vaporisation cools; cohesion supports water columns in plants; cohesion gives surface tension.

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From the examiners' report: There's no examiners' report for this paper, so this tip comes from the mark scheme. Each property needs its 'so': name the property and then what it does. 'Latent heat of evaporation' was rejected, and 'transpiration' alone doesn't count for water columns.

Inorganic ions (3.1.8)

Question 11

AS Paper 1 · June 2022 · Q06.1 · 2 marks · Medium

Explain a property of iron ions that lets them do their job in red blood cells.

Question text: explain a property of iron ions that enables these ions to carry out their role in red blood cells, 2 marks.
Show the mark scheme Mark scheme: charged or polar, or part of haem(oglobin); so binds or associates with oxygen, forms oxyhaemoglobin or transports oxygen.

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From the examiners' report: 71% scored at least one mark. Oxygen binds to haemoglobin; it doesn't 'bond' to it.

Question 12

AS Paper 1 · June 2024 · Q06.1 · 2 marks

Give two roles of phosphate ions in cells.

Question text: give two roles of phosphate ions in cells, 2 marks.
Show the mark scheme Mark scheme: in DNA; in RNA; in ATP or ADP; phosphorylation; in phospholipids (or another phosphate-containing compound such as RuBP or triose phosphate).

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From the examiners' report: All the marking points were seen. Most named DNA and ATP.

Question 13

AS Paper 1 · June 2024 · Q06.2 · 2 marks

Describe the effect of more hydrogen ions on the plasma and its proteins.

Question text: diseased lungs cause carbon dioxide to build up, increasing hydrogen ion concentration in the plasma; describe the effect on the plasma and on the proteins in it, not referring to the Bohr effect, 2 marks.
Show the mark scheme Mark scheme: increased acidity or decreased pH; proteins denature, or their tertiary structure, active site or antigen-binding site changes.

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From the examiners' report: Some said the pH increases: more hydrogen ions means a lower pH. Many then described denaturing or the active site changing shape.

Question 14

AS Paper 1 · June 2024 · Q06.3 · 2 marks

Use a bar chart to describe two patterns in the total ion concentrations in cytoplasm and tissue fluid.

Figure 7: bar chart of inorganic ion concentration in cytoplasm and tissue fluid, with positively charged ions (sodium and other) and negatively charged ions; in each, the total positive equals the negative, and both are higher in the cytoplasm.
Show the mark scheme Mark scheme: equal positive and negative ion concentrations in both (no net charge); higher total ion concentration in the cytoplasm. Ignore sodium ions and 'more ions in the cytoplasm'.

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From the examiners' report: 'Total' was in bold, yet many described sodium ions. Use the axis label: 'a higher total inorganic ion concentration in the cytoplasm' scored, 'more ions in the cytoplasm' didn't.

Question 15

AS Paper 2 · June 2019 · Q09.1 · 5 marks

Describe the roles of iron ions, sodium ions and phosphate ions in cells.

Question text: describe the roles of iron ions, sodium ions, and phosphate ions in cells, 5 marks.
Show the mark scheme Mark scheme: iron in haemoglobin binds oxygen (needed for 5 marks); sodium in co-transport of glucose or amino acids, moved out by the sodium-potassium pump to create a gradient; phosphate in nucleotides and DNA or RNA, in ATP, phosphorylates compounds making them more reactive, hydrophilic part of phospholipids. Reject 'energy produced'.

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From the examiners' report: This discriminated well. Few explained how the sodium gradient is set up by active transport, and saying ATP 'creates' energy cost the phosphate mark.

Calculations with ions (3.1.8)

Question 16

AS Paper 1 · June 2022 · Q06.3 · 2 marks · Hard

Calculate the ratio of the mass of plasma iron ions in a person with haemochromatosis to that in a healthy person.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question text: the mass of iron ions in the plasma of a person with haemochromatosis is 6104 µg; a healthy person's plasma iron ion concentration is 50 µg dm⁻³; blood volume 4000 cm³ in each; calculate the ratio, 2 marks.
Show the mark scheme Mark scheme: 30.52 : 1, 30.5 : 1 or 31 : 1 for 2 marks; 1 mark for 200 µg in the healthy person or an unsimplified ratio such as 6104 : 200.

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From the examiners' report: Only 16% got both marks. Convert 4000 cm³ to 4 dm³, then simplify the ratio to x : 1.

Question 17

AS Paper 1 · June 2018 · Q02.4 · 2 marks · Hard

Calculate the minimum percentage decrease needed to bring a patient's blood H⁺ concentration into the normal range.

Question text: normal blood H⁺ concentration is 3.55 × 10⁻⁸ to 4.47 × 10⁻⁸ mol dm⁻³; a patient has 2.82 × 10⁻⁷ mol dm⁻³; calculate the minimum percentage decrease required, 2 marks.
Show the mark scheme Mark scheme: 84.1% (accept 84.15%); 1 mark for 84, or for (2.82 × 10⁻⁷ − 4.47 × 10⁻⁸) ÷ 2.82 × 10⁻⁷.

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From the examiners' report: Only 12.2% got both and 77.9% scored zero. Keep the standard form, and use the upper end of the normal range for the minimum decrease.

Where students lose marks (from AQA examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Units, not building blocks: Asked what a monomer is, about 40% didn't score. Most gave only 'a small unit' without what it makes, or used 'building blocks', 'atoms' or 'elements'.

    ✔ Gains credit: "A smaller unit/molecule from which larger molecules/polymers are made."

  • Relatively high, relatively large: Only 32% gave three properties of water. Some wrote 'condensation' or 'hydrolysis' as properties, mixed the terms into 'high latent heat capacity', or wrote 'heat capacity' and 'latent heat of vaporisation' without high or large.

    ✔ Gains credit: "Has a (relatively) high heat capacity; has a (relatively) large latent heat of vaporisation."

  • Say what the property does for the organism: Some gave the physics definitions of heat capacity and latent heat without linking them to living organisms, or confused the two terms.

    ✔ Gains credit: "High heat capacity buffers changes in temperature; large latent heat of vaporisation provides a cooling effect through evaporation."

  • Photosynthesis uses water; respiration makes it: Only a third scored on why water uptake differs from transpiration. Almost as many said water is produced in photosynthesis as said it is used, and weaker answers said water is used in respiration.

    ✔ Gains credit: "Water used in photosynthesis; water produced during respiration; water used for support/turgidity."

  • Oxygen binds to haemoglobin: Examiners asked for care with terminology: oxygen binds to (associates with) the iron in haemoglobin, it doesn't 'bond' to it, and some linked oxygen only to red blood cells.

    ✔ Gains credit: "Part of haemoglobin, so binds/associates with oxygen (forms oxyhaemoglobin)."

  • More hydrogen ions, lower pH: It wasn't uncommon for students to say that more hydrogen ions increase the pH.

    ✔ Gains credit: "Decreased (plasma) pH; denatures proteins/changes their tertiary structure."

  • Simplify the ratio to x : 1: Only 16% got both marks for the iron ratio. Many stopped at 6104 : 200 or 763 : 25.

    ✔ Gains credit: "30.5 : 1" (or 31 : 1).

  • Use the top of the normal range: Only 12.2% got the hydrogen ion percentage and 77.9% scored zero. Many ignored the standard form or worked to the lower limit of the normal range instead of the upper one.

    ✔ Gains credit: "(2.82 × 10⁻⁷ − 4.47 × 10⁻⁸) ÷ 2.82 × 10⁻⁷ × 100 = 84.1%."

Download the questions

Download the PDF pack (17 questions, mark schemes at the end)

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Questions, mark schemes and examiners' report extracts © AQA.

Tom Whitburn
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