AQA Biology 4.3.3.1–4.3.3.2
Plant disease and defences
A sick plant can’t tell you what’s wrong. Read the signs, diagnose it, then see how plants fight back.
Triple Science · Higher tier
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Yellow leaves.
A houseplant has been in the same pot for years. Its leaves are slowly turning yellow.
If you had to guess, is that more likely to be a germ, or something missing from the soil?
Plant doctor
What is wrong with this plant?
Plants can be infected by viral, bacterial and fungal pathogens, and damaged by insects. They can also be damaged by ion deficiencies. Look at each plant and diagnose it.
Plant 1 of 5: A short plant, much smaller than the others
Pick a diagnosis.
Understanding ion deficiencies lets growers give plants the best conditions.
Detecting and identifying disease
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.
Plant defences
Three kinds of defence.
Plants have no antibodies. Their defences are physical, chemical and mechanical. Tap each.
TMV and black spot in detail: in Viral diseases and Fungal and protist diseases.
Think again · plants and antibodies
“Plants fight disease with antibodies, like we do.”
Your call
ChooseHow do plants defend themselves?
Sort
Physical, chemical or mechanical?
Place each defence.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Describe
- Each defence and what it does.
- Explain
- Why a deficiency affects growth, link by link.
- Suggest
- A diagnosis or a fix, from the signs.
Key fact
Nitrate deficiency stunts growth; magnesium deficiency causes chlorosis. Plant defences are physical, chemical and mechanical.
Key note · AQA 4.3.3.1–4.3.3.2
Plant disease and defences
- Plants can be infected by viral, bacterial and fungal pathogens and by insects: TMV (virus), black spot (fungus), aphids (insects).
- Ion deficiencies: nitrate (for protein synthesis and growth) causes stunted growth; magnesium (to make chlorophyll) causes chlorosis.
- Physical defences: cellulose cell walls; tough waxy cuticle; bark, dead cells which fall off. Chemical: antibacterial chemicals; poisons.
- Mechanical: thorns and hairs; leaves which droop or curl when touched; mimicry.
- Higher: detect disease by its signs or pests; identify it with a manual or website, a laboratory, or testing kits containing monoclonal antibodies.
Photograph this card. Tomorrow, cover it and say each line first.
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Not sure how to tell the deficiencies apart?
Plant drawings are schematic.