4.1 Defence against pathogens- plants

Question 1

Examples of plants physical barriers to prevent pathogens from entering-

Answer 1

Waxy cuticle of plant leaves, bark on trees, cellulose cell wall

Question 2

How do plants recognise an attack?

Answer 2

Receptors in cells respond to molecules from pathogens/ chemicals produced when the cell wall is attacked, and release signalling molecules which switch on genes and trigger a cellular response

Question 3

Examples of cellular response to pathogen being identified in a plant-

Answer 3

-Production of defensive chemicals
- Sending alarm signals to unaffected cells
-Physically strengthening the cell wall

Question 4

What is callose?

Answer 4

A plant polysaccharide that contains β-1,3 and β-1,6 linkages between glucose
molecules

Question 5

How does callose act as a defence against pathogens?

Answer 5

• Deposited between cell walls and cell membrane in cells next to infected cells which allow it to act as a barrier
• Blocks sieve plates in phloem, sealing off infected part of the cell to prevent spread
• Deposited in plasmodesmata between infected cells and their neighbours to prevent spread

Question 6

What other polysaccharide as well as callose is released to strengthen the mechanical barrier-

Answer 6

Lignin

Question 6

Examples of plants chemical defenses-

Answer 6

• Insect repellents, to deter disease carrying vectors
• Insecticides, which are insect neurotoxins that kill vectors
• Antibiotics, which break down bacterial cell walls
• Anti-fungals, chemicals which are toxic to fungi
• Anti-oomycetes, chemicals which break down protoctista cell walls
• General Toxins

Question 6

What are chitinases?

Answer 6

Hydrolytic enzymes that degrade chitin in fungal cell walls

Question 6

Example of a phenol in plants?

Answer 6

Tanin

Question 6

Purpose of phenols-

Answer 6

Interfere with digestion therefore inhibiting insects from attacking the plant