GCSE Biology Specification

AQA 8461

Section 3.3: Plant disease

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#3.3.1

Detection and identification of plant diseases

Plant diseases can be detected by:
- stunted growth
- spots on leaves
- areas of decay (rot)
- growths
- malformed stems or leaves
- discolouration
- the presence of pests.

Identification can be made by:
- reference to a gardening manual or website
- taking infected plants to a laboratory to identify the pathogen
- using testing kits that contain monoclonal antibodies.


Plants can be infected by a range of viral, bacterial and fungal pathogens as well as by insects.

Knowledge of plant diseases is restricted to tobacco mosaic virus as a viral disease, black spot as a fungal disease and aphids as insects.

Plants can be damaged by a range of ion deficiency conditions:
- stunted growth caused by nitrate deficiency
- chlorosis caused by magnesium deficiency.

Knowledge of ions is limited to nitrate ions needed for protein synthesis and therefore growth, and magnesium ions needed to make chlorophyll.

#3.3.2

Plant defence responses

Students should be able to describe physical and chemical plant defence responses.

Physical defence responses to resist invasion of microorganisms.
- Cellulose cell walls.
- Tough waxy cuticle on leaves.
- Layers of dead cells around stems (bark on trees) which fall off.

Chemical plant defence responses.
- Antibacterial chemicals.
- Poisons to deter herbivores.

Mechanical adaptations.
- Thorns and hairs deter animals.
- Leaves which droop or curl when touched.
- Mimicry to trick animals.