MCQ on Defense Mechanism in Plants
Plant Pathology MCQ E-Books DownloadMCQs on Pre-Existing Structural Defenses
1. What is the main function of cutin and wax in the plant cuticle?
A. Facilitate spore germination
B. Prevent water retention on plant surfaces
C. Increase pathogen colonization
D. Enhance photosynthesis efficiency
Answer: B. Prevent water retention on plant surfaces
2. Which of the following substances in cuticles contributes to the negative charge that repels airborne spores?
A. Suberin
B. Fatty acids
C. Hemicellulose
D. Lignin
Answer: B. Fatty acids
3. What type of enzyme do some pathogens use to dissolve cutin in plant cuticles?
A. Cellulase
B. Pectinase
C. Cutinase
D. Amylase
Answer: C. Cutinase
4. Which plant pathogen produces cutinase to penetrate host plants?
A. Monilinia fructicola
B. Fusarium solani f. sp. pisi
C. Pythium debaryanum
D. Xanthomonas axonopodis pv. citri
Answer: B. Fusarium solani f. sp. pisi
5. How does silicon accumulation in epidermal walls benefit plants?
A. Enhances nutrient absorption
B. Provides resistance against fungal attack
C. Promotes stomatal closure
D. Prevents water loss
Answer: B. Provides resistance against fungal attack
6. The delayed opening of stomata in certain resistant plant varieties is an example of: A. Passive biochemical defense
B. Pre-existing structural defense
C. Post-infection biochemical defense
D. Active pathogen response
Answer: B. Pre-existing structural defense
7. Which natural openings in leaves are often exploited by bacterial pathogens for entry?
A. Stomata
B. Hydathodes
C. Trichomes
D. Lenticles
Answer: B. Hydathodes
8. What is the role of lenticels in plant defense?
A. Prevent spore germination
B. Facilitate gaseous exchange
C. Encourage pathogen entry
D. Provide resistance after suberization
Answer: D. Provide resistance after suberization
9. Thick epidermis and compact palisade layers in groundnut varieties help resist which pathogen?
A. Pythium debaryanum
B. Cercospora leaf spots
C. Xanthomonas axonopodis
D. Ascochyta rabiei
Answer: B. Cercospora leaf spots
10. High hair density on chickpea leaves and pods provides resistance to: A. Monilinia fructicola
B. Pythium debaryanum
C. Ascochyta rabiei
D. Fusarium solani
Answer: C. Ascochyta rabiei
MCQs on Pre-Existing Biochemical Defenses
11. What is the primary action of pre-existing biochemical defenses in plants?
A. Stimulate stomatal opening
B. Inhibit pathogen activities
C. Increase plant photosynthesis
D. Promote cuticle formation
Answer: B. Inhibit pathogen activities
12. The toxic or lytic effect of pre-existing plant chemicals on pathogens is an example of: A. Indirect action
B. Constitutive biochemical defense
C. Induced structural defense
D. Wound healing response
Answer: B. Constitutive biochemical defense
13. Which of the following is NOT a pre-existing structural defense mechanism?
A. Thick cuticle
B. Suberized cork cells
C. Wound antibiotics
D. Hairy leaf surface
Answer: C. Wound antibiotics
14. Suberin is associated with: A. Cuticle thickness
B. Epidermal wall toughness
C. Stomatal movement
D. Pathogen colonization
Answer: B. Epidermal wall toughness
15. The sugary nectar secreted by nectaries in inflorescences acts as a barrier by: A. Attracting pathogens
B. Preventing fungal spore germination
C. Supporting antagonistic microflora
D. Enhancing pathogen entry
Answer: C. Supporting antagonistic microflora
16. What characteristic of resistant potato tubers helps defend against Pythium debaryanum?
A. High fiber content
B. Low water retention
C. Increased trichome density
D. Delayed stomatal opening
Answer: A. High fiber content
17. Which plant opening serves as a weak point for pathogen entry unless suberized?
A. Hydathodes
B. Stomata
C. Lenticels
D. Nectaries
Answer: C. Lenticels
18. Groundnut varieties resistant to Cercospora leaf spots have: A. Larger stomata
B. Thin epidermal layers
C. Thick epidermis and high trichome density
D. Suberized lenticels
Answer: C. Thick epidermis and high trichome density
19. Pre-existing structural defenses in plants are also known as: A. Active infection defenses
B. Anti-infection structures
C. Induced biochemical barriers
D. Passive biochemical defenses
Answer: B. Anti-infection structures
20. What is the primary role of plant trichomes in defense?
A. Absorb nutrients
B. Resist pathogen entry
C. Enhance transpiration
D. Promote stomatal movement
Answer: B. Resist pathogen entry
21. Which of the following substances released by plants can affect the phyllosphere and rhizosphere microflora?
A. Sugars and amino acids
B. Organic acids and glycosides
C. Enzymes and inhibitory substances
D. All of the above
Answer: D
22. What compounds in resistant plant varieties form the basis of resistance to certain pathogens?
A. Proteins and carbohydrates
B. Tannins and dienes
C. Minerals and salts
D. Water-soluble vitamins
Answer: B
23. Saponins in plants serve as: A. Nutritional factors for pathogens
B. Antifungal agents with membranolytic activity
C. Growth factors for bacteria
D. Stimulants for parasitic fungi
Answer: B
24. The absence of which essential factor can render a pathogen-host interaction ineffective?
A. Host recognition molecules
B. Sufficient sunlight
C. Water supply to pathogens
D. External physical barriers
Answer: A
25. How do phenolic compounds act in plant defense?
A. They promote pathogen growth
B. They function as toxic inhibitors of hydrolytic enzymes
C. They act as structural barriers against pathogens
D. They dissolve pathogen cell walls
Answer: B
26. Recognition factors in plants help in:
A. Blocking stomatal openings
B. Identifying host-specific pathogens
C. Absorbing essential nutrients for pathogens
D. Activating phytoalexin production
Answer: B
27. Host receptors and toxin-sensitive sites are critical for:
A. Nutrient uptake in pathogens
B. Pathogen-specific disease development
C. Biochemical defense initiation
D. Epidermal layer lignification
Answer: B
28. Which structural defense mechanism involves lignin deposition in cell walls?
A. Tyloses formation
B. Lignification
C. Suberization
D. Gum deposition
Answer: B
29. Cork layer formation in plants serves to:
A. Enhance water absorption
B. Protect against abiotic stress
C. Isolate infected cells from healthy tissues
D. Increase nutrient flow to infected areas
Answer: C
30. What is the role of tyloses in plant defense?
A. Inducing phenolic compound production
B. Blocking xylem vessels to prevent pathogen spread
C. Promoting pathogen spore germination
D. Enhancing cell-to-cell communication
Answer: B
31. Which process involves the shedding of infected leaves or plant parts to halt pathogen spread?
A. Lignification
B. Suberization
C. Abscission layer formation
D. Gum deposition
Answer: C
32. What is the function of induced histological defenses in plants?
A. Promote pathogen colonization
B. Strengthen the infected tissues
C. Create barriers for further colonization
D. Facilitate toxin secretion by pathogens
Answer: C
33. Callose deposition in plant cells helps in:
A. Promoting pathogen enzyme activity
B. Preventing nutrient flow to pathogens
C. Delaying contact of pathogens with host cells
D. Absorbing excess moisture
Answer: C
34. How do structural proteins contribute to plant defense?
A. By forming physical barriers
B. By enhancing pathogen growth
C. By breaking down pathogen proteins
D. By promoting vascular tissue repair
Answer: A
35. What is the significance of induced cytoplasmic defense in plants?
A. Effective against weak pathogens or slow-growing parasites
B. Rapid elimination of strong pathogens
C. Immediate repair of infected tissues
D. Structural reinforcement of vascular tissues
Answer: A
36. Phytoalexins are: A. Antibiotics produced in plant-pathogen interactions
B. Nutrients for host-specific pathogens
C. Structural components of epidermal cells
D. Water-soluble growth factors for fungi
Answer: A
37. The production of phytoalexins is often triggered by:
A. Nutrient deficiency
B. Abiotic stress or biotic interactions
C. Suberization of cell walls
D. Enhanced sunlight exposure
Answer: B
38. Which of the following chemicals is NOT considered a phytoalexin?
A. Chlorogenic acid
B. Avenacin
C. Hydroquinone
D. Sucrose
Answer: D
39. Toxic substances in plants are effective due to:
A. Rapid production and accumulation
B. Their ability to act as structural barriers
C. Neutralizing pathogen enzymes slowly
D. Being absorbed by pathogens for growth
Answer: A
40. The concept of phytoalexins was first proposed based on studies involving:
A. Potato and Phytophthora infestans
B. Wheat and Septoria nodorum
C. Cucumber and Cladosporium cucumerium
D. Tomato and Fusarium oxysporum
Answer: A
41. The role of phenyl ammonia lyase (PAL) in plant defense includes:
A. Hydrolyzing pathogen cell walls
B. Synthesizing phenols, phytoalexins, and lignin
C. Neutralizing pathogen toxins
D. Blocking nutrient flow to pathogens
Answer: B
42. The effectiveness of plant resistance largely depends on:
A. The speed and amount of synthesized defensive products
B. The absence of pathogens in nearby tissues
C. The thickness of the epidermal layer
D. The genetic diversity of the pathogen
Answer: A
43. Catechol-tannin in immature grape fruits inhibits:
A. Pathogen toxins
B. Phenol synthesis
C. Enzymes produced by Botrytis cinerea
D. Pathogen recognition molecules
Answer: C
44. Resistance to toxins in plants can be achieved by:
A. Increasing lignin synthesis
B. Detoxification or lack of receptor sites
C. Rapid cell wall thickening
D. Blocking the production of phytoalexins
Answer: B
45. The Shikimic acid pathway is crucial in plant defense for:
A. Enhancing photosynthesis
B. Synthesizing defense-related substances
C. Producing growth hormones
D. Inhibiting protein synthesis in pathogens
Answer: B
46. Increased respiration in diseased tissue is often accompanied by:
A. Decreased metabolic activity in healthy tissues
B. Replacement of glycolysis with the pentose phosphate pathway
C. Reduction in phenolic compound synthesis
D. Immediate cell death in infected areas
Answer: B
47. Active defense responses in plants can result in:
A. Increased pathogen colonization
B. Incompatible host-pathogen interactions
C. Enhanced susceptibility to subsequent infections
D. Nutrient flow from healthy to infected tissues
Answer: B
48. Hypersensitive reactions in plants are associated with:
A. Accelerated pathogen growth
B. Rapid cell death and increased resistance
C. Reduced metabolic activity in infected tissues
D. Uniform resistance across all plant parts
Answer: B
49. Which compound plays a key role in detoxifying pathogen toxins?
A. Phytoalexins
B. Phenolic oxidized products
C. Structural proteins
D. Glycoproteins
Answer: B
50. What happens when the spread of a pathogen is checked?
A. Neighboring tissues are sacrificed
B. Damaged parts are isolated with new tissue formation
C. Defensive barriers are dismantled
D. The pathogen develops resistance to host defenses
Answer: B
51. Systemic acquired resistance (SAR) in plants is comparable to:
A. Human immunization but with different mechanisms
B. Antibiotic resistance in bacteria
C. Increased photosynthetic activity
D. Nutrient redistribution in plants
Answer: A
52. The signal molecules in systemic induced resistance:
A. Remain localized to the infection site
B. Propagate resistance to distant plant parts
C. Inhibit photosynthesis
D. Destroy nearby plant tissues
Answer: B
53. Which of the following is NOT associated with induced resistance in plants?
A. Accumulation of PR proteins
B. Activation of lignin synthesis
C. Enhanced pathogen growth
D. Increased peroxidase activity
Answer: C
54. The principle of induced resistance involves:
A. Direct destruction of pathogens at the infection site
B. Systemic activation of defense mechanisms through signal compounds
C. Immediate lignification of all plant tissues
D. Blocking sunlight to infected tissues
Answer: B
55. Which pathway is essential for synthesizing defense-related compounds in plants?
A. Calvin cycle
B. Shikimic acid pathway
C. Citric acid cycle
D. Glycolysis
Answer: B
56. Induced biochemical defenses in plants are triggered by:
A. Accumulation of essential nutrients
B. Stress caused by increased metabolic activity
C. Reduced photosynthetic rates
D. Enhanced pathogen colonization
Answer: B
57. What role do PR proteins play in induced resistance?
A. They deactivate host enzymes
B. They act as defensive proteins against pathogens
C. They enhance pathogen attachment
D. They suppress host metabolic activity
Answer: B
58. In post-infectional defense, phenol-oxidizing enzymes:
A. Promote pathogen growth
B. Neutralize pathogen enzymes and toxins
C. Inhibit photosynthesis in infected tissues
D. Reduce phenolic compound synthesis
Answer: B
59. Which factor is essential for systemic acquired resistance (SAR) in plants?
A. Constant exposure to pathogens
B. The presence of signal compounds
C. A single line of pre-existing defense
D. Reduced metabolic activity in infected tissues
Answer: B
60. The pentose phosphate pathway in diseased tissues contributes to:
A. Enhanced glycolysis
B. Production of four-carbon compounds
C. Increased lignin breakdown
D. Reduced respiration rates
Answer: B