Plant Surfaces Block Pathogen Entry

1. The cellulose cell wall surrounds each plant cell and resists penetration by pathogens.
2. Bark contains layers of dead cells that form a tough barrier around older stems.
3. Cellulose microfibrils give cell walls tensile strength, resisting penetration and limiting the spread of pathogens between cells.
4. Bark is formed from layers of dead cells and contains waterproof substances, creating a thick barrier that is difficult for pathogens to cross.
5. The waxy cuticle forms a waterproof physical barrier over the epidermis, making it difficult for pathogens to enter leaf cells.

Damage Weakens Physical Defences

1. Cuts, insect feeding and damaged roots create openings through which pathogens can enter.
2. A plant may seal damaged tissue by depositing extra material around the wound.
3. The waxy cuticle is continuous over most of the leaf surface, so a pathogen must pass through a stomatal opening or damaged tissue to reach living cells.
4. If a pest breaks a barrier while feeding, the wound exposes living tissue and provides moisture and nutrients that support pathogen growth.

Match Structure to Function

1. The cuticle covers the leaf surface, the cell wall surrounds each cell, and bark protects older stems.
2. Each structure reduces contact between pathogens and living cell contents.

Separate Barriers From Chemicals

1. A physical barrier blocks entry through its structure, while a chemical defence kills pathogens or deters pests.
2. The two types can act together, but they should not be confused in an answer.