AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), 2020: Question 3

9 marks · Standard Demand difficulty · Extended Answer

Identify the plant part that absorbs nitrate ions, name two other chemicals cycled in ecosystems, and describe the role of microorganisms in recycling chemicals for new plant growth.

Practise this question

Question

The image shows three sub-questions about mineral ions and chemical cycling in an ecosystem. Question 03.1 asks which part of a plant takes in nitrate ions. Question 03.2 asks to name two chemicals cycled between plants, soil, and air, excluding nitrogen or nitrates. Question 03.3 is a 6-mark extended response question asking to describe how microorganisms recycle chemicals and how those chemicals are used by new plants.
Question text

03 Mineral ions are important chemicals in an ecosystem.

03.1 Plants take in nitrate ions dissolved in water.

Which part of a plant takes in nitrate ions?

[1 mark]

03.2 Name two chemicals that are cycled between plants, the soil and the air.

Do not refer to nitrogen or nitrates in your answer.

[2 marks]

03.3 All the chemicals in a plant are recycled when the plant dies.

Describe how:

• microorganisms recycle chemicals

• the chemicals are used again by new plants.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme provides the answers for the three sub-questions. Question 03.1 accepts 'root' or 'root hairs'. Question 03.2 accepts 'carbon' (or carbon dioxide) and 'water' (or oxygen). Question 03.3 is a level-marked response describing the decay process, respiration, release of carbon dioxide, and its subsequent use in photosynthesis by new plants, as well as the release of mineral ions into the soil.

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 root (hairs) 1 AO1

4.7.2.2

4.2.3.2

03.2 in either order AO1

4.7.2.2

carbon allow carbon dioxide 1

water 1

if no other mark awarded allow

oxygen for 1 mark

03.3 Level 2: Scientifically relevant facts, events or processes are 4–6

AO1

identified and given in detail to form an accurate account. 4.7.2.2

4.4.1.1

Level 1: Facts, events or processes are identified and simply 1–3 4.4.2.1

stated but their relevance is not clear.

No relevant content 0

Indicative content

• microorganisms decay (the dead plant)

• microorganisms respire

• using carbon compounds / glucose

• releasing carbon dioxide

• into the atmosphere

• new plants take in carbon dioxide

• (carbon dioxide) for photosynthesis

• making glucose

• converted into correctly named cell materials

(when plants are decayed)

Nitrate / mineral ions

• are released into soil

• to be taken up by new growing plants

Water

• plants dehydrate or water evaporates when they die

• recycled as rain needed by growing plants

Total 9

How to answer it

Nutrient Cycling in Ecosystems

What this question tests:
This question assesses your understanding of how materials are recycled through the environment. You need to recall plant anatomy (uptake of ions), identify common substances in cycles (carbon and water), and explain the role of microorganisms in decomposition and the subsequent re-uptake by plants.

Part (a): Plant Anatomy

Correct Answer

Root (or root hairs).

Key Knowledge

Root hairs provide a large surface area to increase the rate of absorption of water and mineral ions by osmosis and active transport.

Part (b): Cycling Chemicals

Correct Answer

Any two of: Carbon, Water, Oxygen.

Common Errors

Students often lose marks here by ignoring the instruction: "Do not refer to nitrogen or nitrates." Always read the negative constraints in the question carefully!

Part (c): The Process of Recycling (6 Marks)

Exam Technique: Level of Response

This is a 6-mark "extended response" question. To reach Level 2 (4-6 marks), you must provide a detailed, logical account linking decomposition to plant growth. Use bullet points or clear paragraphs to ensure you cover both parts of the prompt.

Key Knowledge: The Cycle

  • Decomposition: Microorganisms (bacteria/fungi) break down dead plant matter.
  • Respiration: As they decay the material, microorganisms respire, releasing CO₂ into the atmosphere.
  • Re-uptake: New plants take in this CO₂ for photosynthesis to produce glucose.
  • Soil Nutrients: Mineral ions (like nitrates) are released into the soil during decay and are absorbed by new roots.
  • Water: Water is released into the environment and recycled as rain.

Examiner Commentary

Top-level responses clearly linked the release of chemicals by microorganisms to the uptake by new plants. Don't just list facts—explain the flow of the materials.

Topics

Biology · B7: Ecology

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Foundation), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.