4.1.3- Plant Defences

Question 1

What is a passive defence?

Answer 1

Defences that are present before a living thing becomes infected and are there to prevent the pathogen entering me the organism and therefore spreading.

Question 2

List the seven physical (passive) defences a plant has against pathogens.

Answer 2

Cellulose cell wall// waxy cuticle// bark// callose// stomata like closure// tylose formation// lignin cell wall thickening.

Question 3

Explain how the cellulose cell wall acts as a physical, passive defence against pathogens.

Answer 3

It acts as a physical barrier and contains a variety of chemicals that can be activated once a pathogen enters the cell.

Question 4

How does the Lignin cell wall thickening act as a passive defence against pathogen entry to a plant?

Answer 4

The lignin is waterproof and almost completely indigestible.

Question 5

explain how the waxy cuticle of a cell acts as a passive (physical) defence to pathogen entry to the cell.

Answer 5

Pathogens collect in water and need it to survive- the waxy cuticle stops water from collecting on the surface of the cell.

Question 6

How does bark act as a physical passive defence for a plant?

Answer 6

Bark contains a variety of chemical defences that work against the pathogenic organisms.

Question 7

Explain how stomataI closure can be a passive physical defence for plants, against pathogens.

Answer 7

Guard cells close the stomata when a pathogen is detected- preventing entry of the pathogen to the plant.

Question 8

Explain how callose acts as a passive, physical defence against pathogens in plants.

Answer 8

It stops the pathogen spreading around the plant by deposition in the phloem’s sieve plates after growing season.

Question 9

What is a tylose?

Answer 9

A balloon like swelling or projection that fills the xylem vessel in a plant cell.

Question 10

Explain how the formation of tylose can act as a passive, physical defence against pathogen entry to a plant cell.

Answer 10

It blocks the xylem when it is fully formed, stopping water being carried in the tube and preventing the pathogen spreading. It also had a high concentration of chemicals (eg terpenes) that are toxic to pathogens.

Question 11

What are chemical (passive) defences for prevention of pathogen entry to plants?

Answer 11

Defences present before the infection, but which are mostly produced once the plants infected- due to the production of the chemicals needing a lot of energy.

Question 12

What are active defences for plant protection?

Answer 12

They’re defences that are activated when a plant becomes infected- they result in the production of defensive chemicals and the increasing of the plants existing physical defences.

Question 13

What are the six main active defences that a plant can activate when a plant is infected with a pathogen?

Answer 13

• oxidative bursts
• defensive chemical production is increased
• callose is deposited near the pathogen- blocks plasmodesmata and strengthens cell wall- cell wall’s thickened and strengthened
• necrosis
• canker

Question 14

Explain how oxidative bursts can act as an active defence in plants.

Answer 14

The bursts produce highly reactive oxygen molecules that are capable of damaging the cells of the invading pathogen.

Question 15

List four types f chemical defences a plant has against pathogens

Answer 15

Terpenoids
Phenols
Alkaloids
Hydrolytic Enzymes

Question 16

What is a canker?

Answer 16

A sudden necrotic lesion that occurs in the woody tissue of a plant.

Question 17

What is necrosis?

Answer 17

Deliberate cell suicide- when the cells around a pathogen are killed to stop the pathogen spreading and to save the rest of the plant.

Question 18

Define what callose is.

Answer 18

A large polysaccharide that deposits in the sieve tubes of the phloem after growing season as a passive, physical defence against pathogens.