MODULE 7 IQ2: Responses to Pathogens

Question 1

biotroph

Answer 1

pathogenic organism that are completely dependent on host cells for their nutrient acquisition and can secrete effectors to suppress or regulate plant defence. derive nutrients and energy from living cells
- e.g. bacteria and virus

Question 2

2 main groups of plant pathogens

Answer 2

biotroph, nectotroph

Question 3

nectotroph

Answer 3

pathogenic organisms that derive their energy from dead or dying cells
- e.g. fungi

Question 4

passive defence (physical barriers) in plants

Answer 4

• secretion of enzymes
• thicker cuticles
• thick bark –> external layer of dead cells
• vertical hanging leaves which do not accumulate a water film
• stomata open during humid weather
• thorns or spines

Question 5

passive defence (chemical barriers) in plants

Answer 5

• chemical compounds in tissues of plants
• produces enzymes that break down pathogen-derived toxins
• chemical receptors on plant cells can detect presence of pathogen & activate next stage of defence

Question 6

active defence in plants: 3 major groups of responses

Answer 6

pathogen recognition, rapid active response, delayed active response

Question 7

pathogen recognition in plant’s active defence

Answer 7

• plants recognise pathogens by detecting certain physical & chemical signals
• genes within cells of plant regulate plant responses
• causes change in permeability of plant cell membrane

Question 8

rapid active response in plant’s active defence

Answer 8

• can turn genes on & off
• when plant is wounded, chemicals are activated at feeding sites
• produces key compound called jasmonic acid (JA) –> “master regulator” of induced plant defences
• damages digestive systems of herbivores
• disrupts cell functions that are critical for herbivore growth, survival or reproduction

Question 9

delayed active response in plant’s active defence

Answer 9

• limits spread of pathogen
• repairs wounds in bark through cork cell production and gum secretion
• lysozyme-like chemicals are released and have an antimicrobial action
• salicylic acid acts as a signalling agent of subsequent infections and play a role in plant’s memory of particular pathogen

Question 10

myrtle rust

Answer 10

pathogenic fungus called ‘Austropuccina psidii’
- attacks soft, actively growing leaves, shoot tips and young stems
- death of soft plant material
- releases small protein molecules, called effectors into plant cell –> if plant can detect the fungal effector molecules it may stop fungal infections

Question 11

animal 3 responses to pathogen

Answer 11

physical barriers, chemical barriers, microbiological barriers

Question 12

physical barriers in animal responses

Answer 12

• epithelial cells –> line skin as well as respiratory, gastrointestinal and urogenital tracts
• mucus-secreting membranes trap invading organisms in mucus and membranes lined with cilia sweeping foreign bodies away

Question 13

chemical barriers in animal responses

Answer 13

• lysosome enzymes and toxic metabolites provide generalised defence
• stomach acid and digestive enzymes that kills pathogens
• fluid in lungs coat pathogens, making it easier for pathogens to be eliminated by macrophages
• lining in vagina is coated with acidic secretions