Plant Pathogens And Defences

Question 1

Direct plant transmission

Answer 1

Soil borne (roots) 
Airborne (spores carried by wind)
Plant parts (infected vascular system spread pathogens)

Question 2

Indirect plan transmission

Answer 2

Spores / bacteria attached to insects e.g. Beetles spread Dutch elm disease

Question 3

Passive physical defences in plants

Answer 3

Cellulose cell wall
Lignin thickening of cell wall
Waxy cuticles
Bark
Stomatal closure
Callose - large polysaccharide deposited in siege tubes (phloem)
Tylose formation - balloon like swelling fills xylem vessel

Question 4

Active defences in plants

Answer 4

Cell walls thickened + strengthened with additional cellulose

Deposition of callose

Oxidative bursts - produce highly reactive oxygen molecules capable of damaging cells of invading organisms

Increase in production of chemicals

Canker - sunken necrotic lesion in woody tissue , affected area eventually breaks off

Necrosis - deliberate cell suicide surrounding infection.

Question 5

Terpenoids

Answer 5

Essential oils with antibacterial and antifungal properties, creates scent

Question 6

Phenols

Answer 6

Tannins in bark inhibit attack by insects. Bind to salivary proteins and digestive enzymes, deactivating them
Insects with lots of tannins eventually die, reducing transmission

Question 7

Hydrolytic enzymes

Answer 7

Found in spaces between cells

Chitinases - break down chitin in fungal cell walls

Gluconases - hydrolyse glycosidic bonds in glucans

Lysozymes - capable of degrading bacterial cell walls

Question 8

Defensive proteins

Answer 8

Small cysteine rich proteins that have anti microbial activity
Act upon molecules in plasma membrane and inhibit action of ion transport channels

Question 9

Alkaloids

Answer 9

Nitrogen containing compounds
Bitter taste to put off herbivores
Act on variety of metabolic reactions, inhibiting enzyme action + protein synthesis