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Plants are constantly exposed to pathogens including bacteria, viruses, fungi, and insects. Unlike animals, plants do not have a mobile immune system with specialised immune cells. Instead, they rely on a combination of physical barriers, chemical defences, and inducible responses. This lesson covers plant defence mechanisms as required by the Edexcel A-Level Biology (9BI0) specification.
Plants are sessile (non-motile) organisms that cannot flee from pathogens. They are exposed to a wide range of threats:
| Threat | Examples |
|---|---|
| Bacterial pathogens | Agrobacterium tumefaciens (crown gall), Pseudomonas syringae (leaf spot) |
| Viral pathogens | Tobacco mosaic virus (TMV), cauliflower mosaic virus |
| Fungal pathogens | Phytophthora infestans (potato blight), Botrytis cinerea (grey mould) |
| Herbivorous insects | Aphids, caterpillars, beetles |
Exam Tip: Plants do not have an adaptive immune system like animals. They cannot produce antibodies or have immune memory. All plant defences are innate (non-specific or pattern-recognition based).
Plants have several physical barriers that prevent pathogen entry:
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