3.3.1: Detection and identification of plant diseases
Not started yet — this one needs some love.
Signs of plant disease (detection): stunted growth, spots on leaves, areas of decay (rot), abnormal growths, malformed stems or leaves, discolouration, presence of pests.
Identification methods: reference to gardening manual or website; sending infected plant to laboratory to identify pathogen; testing kits containing monoclonal antibodies.
Plant diseases to know: TMV (viral), rose black spot (fungal), aphids (insects).
Ion deficiencies:
Nitrate deficiency → stunted growth (nitrates needed for amino acid and protein synthesis, which is needed for growth).
Magnesium deficiency → chlorosis (yellowing of leaves; magnesium is needed to produce chlorophyll).
Common exam mistakes
Chlorosis (yellowing of leaves) is caused by magnesium deficiency — NOT nitrate deficiency.
Stunted growth is caused by nitrate deficiency — NOT magnesium deficiency.
Three distinct terms to understand: chlorophyll (the pigment), chloroplasts (the organelle), chlorosis (the yellowing condition) — do not confuse.
For full marks on magnesium deficiency: magnesium → chlorophyll → light absorption → photosynthesis → glucose → growth. Must show the chain of reasoning.
Lack of magnesium does NOT directly cause stunted growth — it causes lack of chlorophyll, which reduces photosynthesis, which reduces glucose, which limits growth.