This exam tips covers Exam Technique Tips within Plant Diseases and Defenses for GCSE Biology. Plant pathogens, defense mechanisms, disease identification, crop protection It is section 18 of 18 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 18 of 18
Practice
18 questions
Recall
20 flashcards
Exam Technique Tips
Name both diseases and their pathogen type. If asked to give an example of a plant disease, always give the full name (rose black spot) AND state it is caused by a fungus. One-word answers like "black spot" or "fungus" alone often score zero.
Explain the full consequence chain for TMV. Questions often ask you to explain why TMV reduces growth. The chain is: virus disrupts chloroplasts → mosaic pattern of reduced chlorophyll → less light absorbed → less photosynthesis → less glucose → less energy for growth → stunted plant. Each arrow represents a mark point.
Distinguish physical from chemical — do not mix them up. Physical defenses prevent pathogen entry (cuticle, cell walls, bark, thorns). Chemical defenses kill or slow pathogens that have entered (antimicrobial compounds, toxins). In a "describe two defense mechanisms" question, you need one of each type for full marks.
When comparing plant and animal defenses, be specific. Do not write "plants have a weaker immune system" — this scores zero. Write: "plants lack mobile immune cells and specific antibodies; instead they rely on physical barriers such as the waxy cuticle and chemical compounds such as antimicrobial proteins".
Control variables in plant disease investigations. If asked to design an experiment testing a fungicide, your control variables must include: temperature, light intensity, water availability, plant species, plant age, and volume/concentration of fungicide applied. Always state why each variable must be kept constant.
Spread of rose black spot — include conditions. Exam mark schemes often award a mark for stating that spores spread in moist/wet conditions or via water splash/wind. Do not just write "spores spread" — add the mechanism and environmental conditions for full credit.