12.4 Plant Defences Against Pathogens

Question 1

How do plants recognise an attack?

Answer 1

Some molecules from the pathogen are recognised by the plant cell
When pathogenic enzymes break down the cell wall, the breakdown products are recognised
Signalling molecules alert nucleus to attack
Callose and lignin and made to strengthen the cell walls
Defensive chemicals alert other cells before they are attacked
Some defensive chemicals attack the pathogen directly

Question 2

Structure of callose

Answer 2

Polysaccharide
Beta 1,3 and 1,6 linkages between glucose monomers

Question 3

Function of callose in physical defence

Answer 3

Callose synthesised and deposited between cell walls - acts as barriers to prevent spread of pathogen
Lots of callose and lignin are added which makes the barrier to invasion thicker and stronger
Callose blocks sieve plates in the phloem - seals off infected parts and prevents the spread of pathogens
Deposited at the plasmodesmata - sealing off infected cells from healthy cells

Question 4

Chemical defences in plants

Answer 4

Insect repellents
Insecticides
Antibacterial compounds (phenols)
Antifungal compounds or chitinases (infer with cell membranes of fungi)
Anti-oomycetes - chemicals that can be broken down to make cyanide compounds when the plant cell is attacked