Explain how a gardener could identify that a plant is suffering from a mineral ion deficiency rather than a pathogen infection.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants can show symptoms of disease for different reasons. Some symptoms are caused by pathogens, whilst others result from a lack of mineral ions in the soil.
Model answer (4 marks)
1. A deficiency shows a specific pattern – e.g. stunted growth with normal leaf shape for nitrate, or uniform yellowing of older leaves with green margins for magnesium.
2. The gardener can analyse the soil or use a test kit to check the level of the suspected ion.
3. If the ion is low, adding the missing mineral and observing symptom improvement confirms a deficiency.
4. Pathogens usually give spots, lesions, mould or decay, which are not seen in a simple ion deficiency.
5. A testing kit, laboratory analysis or a reference guide can be used to distinguish between a pathogen and a mineral ion deficiency.
2. The gardener can analyse the soil or use a test kit to check the level of the suspected ion.
3. If the ion is low, adding the missing mineral and observing symptom improvement confirms a deficiency.
4. Pathogens usually give spots, lesions, mould or decay, which are not seen in a simple ion deficiency.
5. A testing kit, laboratory analysis or a reference guide can be used to distinguish between a pathogen and a mineral ion deficiency.
Examiner tips
- Use the word ‘specific pattern’ to show you know the symptoms of a deficiency. Show the step of testing the soil or using a kit. Explain that improvement after adding the ion confirms a deficiency. Mention that pathogen signs are different (spots, lesions).
Common mistakes
- Confusing general yellowing with a specific ion deficiency. Assuming all symptoms are due to pathogens. Not mentioning the need to test the soil or add the ion to confirm.
Mark scheme (4 marks)
- Mineral ion deficiency causes specific symptoms such as stunted growth (nitrate deficiency) or chlorosis / yellowing of leaves (magnesium deficiency)
- Testing / treating the soil or adding the missing mineral ion and seeing if symptoms improve confirms a deficiency
- Pathogen infections often produce visible signs such as spots, lesions, growths, or decay on the plant
- A gardener could use a testing kit / laboratory analysis / reference guide to identify the specific pathogen or mineral ion deficiency
Key terms in this question
mineral ion deficiency · pathogen
Related
- Revision notes: Plant disease (Bio only) →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →