A farmer uses an NPK fertiliser to increase crop yields. The NPK fertiliser contains ammonium nitrate, potassium chloride and ammonium phosphate. Explain how each of the three elements — nitrogen, phosphorus and potassium — improves the growth of crops.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
NPK fertilisers contain compounds of nitrogen, phosphorus and potassium. These fertilisers improve agricultural productivity.
Model answer (4 marks)
Nitrogen is essential for the synthesis of proteins and chlorophyll, which promotes vigorous leaf and shoot growth.
Phosphorus is required for energy transfer (ATP) and nucleic acid synthesis, supporting root development and overall plant respiration.
Potassium acts as an enzyme activator, regulating photosynthesis and respiration, and it promotes flower and fruit formation.
When crops lack sufficient N, P or K, they exhibit reduced growth, poor yield and characteristic deficiency symptoms.
Phosphorus is required for energy transfer (ATP) and nucleic acid synthesis, supporting root development and overall plant respiration.
Potassium acts as an enzyme activator, regulating photosynthesis and respiration, and it promotes flower and fruit formation.
When crops lack sufficient N, P or K, they exhibit reduced growth, poor yield and characteristic deficiency symptoms.
Examiner tips
- Use the exact phrases from the mark scheme (e.g., ‘promotes leaf/shoot growth’).
- Show each element’s role separately – one sentence per element.
- Mention the consequence of deficiency to link all three.
Common mistakes
- Mixing up the roles of nitrogen and phosphorus; e.g., saying nitrogen is for root growth.
- Omitting the link between potassium and enzyme activity.
Mark scheme (4 marks)
- Nitrogen promotes/is needed for leaf/shoot growth OR nitrogen is needed to make proteins/chlorophyll in plants
- Phosphorus promotes/is needed for root growth OR phosphorus is needed for respiration/photosynthesis (cell processes)
- Potassium helps enzymes work / promotes flower and fruit growth / is needed for photosynthesis and respiration
- Without sufficient NPK nutrients, plants show deficiency symptoms / reduced growth / lower crop yield
Key terms in this question
nitrogen · phosphorus · potassium
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More The Haber process and the use of NPK fertilisers (Chem only) questions
- NPK fertilisers contain compounds of nitrogen, phosphorus and potassium. Explain…
- The Haber process is used to manufacture ammonia, which can be used to make NPK …
- Ammonia produced by the Haber process can be converted into nitric acid, which i…
- A company manufactures NPK fertilisers using ammonia from the Haber process. Exp…