Unit 5 - Practice Quiz

PTH103 50 Questions
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1 Which of the following terms describes an organism that lives primarily as a saprophyte but can live as a parasite when the opportunity arises?

A. Biotroph
B. Facultative saprophyte
C. Facultative parasite
D. Obligate parasite

2 Which type of pathogen requires a living host to complete its life cycle and cannot be grown on artificial culture media?

A. Necrotroph
B. Facultative saprophyte
C. Hemibiotroph
D. Obligate parasite (Biotroph)

3 In the context of variability in fungal pathogens, what is the phenomenon where genetically different nuclei coexist within a common cytoplasm?

A. Transformation
B. Heterokaryosis
C. Mutation
D. Hybridization

4 Which mechanism of variability is unique to fungi that lack a sexual cycle (Fungi Imperfecti), involving the fusion of haploid nuclei within a heterokaryon followed by haploidization?

A. Parasexuality
B. Transduction
C. Conjugation
D. Meiosis

5 Which enzyme is primarily responsible for the degradation of the plant cuticle during the initial stages of pathogen penetration?

A. Cutinase
B. Pectinase
C. Ligninase
D. Cellulase

6 Soft rot symptoms in vegetables are primarily caused by the action of which group of enzymes that degrade the middle lamella?

A. Pectinases
B. Amylases
C. Proteases
D. Lipases

7 Which of the following is considered a Host-Specific Toxin (HST)?

A. Victorin (HV-toxin)
B. Tentoxin
C. Tabtoxin
D. Phaseolotoxin

8 What is the primary function of the enzyme Polygalacturonase (PG) in pathogenesis?

A. It detoxifies phytoalexins.
B. It degrades cellulose microfibrils.
C. It removes methoxyl groups from pectin chains.
D. It hydrolyzes the glycosidic bonds between galacturonic acid residues in pectin.

9 Which growth regulator is responsible for the 'Bakanae' or 'foolish seedling' disease in rice, characterized by excessive stem elongation?

A. Indole-3-acetic acid (IAA)
B. Ethylene
C. Gibberellin
D. Cytokinin

10 The formation of 'Green Islands' around infection spots in rust and mildew diseases is attributed to the localized accumulation of which growth regulator?

A. Abscisic Acid
B. Cytokinins
C. Ethylene
D. Gibberellins

11 Which term describes enzymes that are always produced by the pathogen regardless of the presence of the substrate?

A. Adaptive enzymes
B. Extracellular enzymes
C. Constitutive enzymes
D. Inducible enzymes

12 Wildfire disease of tobacco is associated with which non-host-specific toxin?

A. Tabtoxin
B. Amylovorin
C. T-toxin
D. HC-toxin

13 Hypertrophy in plant tissues, often seen in tumorous diseases like Crown Gall, refers to:

A. Death of cells
B. Fusion of cells
C. Increase in cell size
D. Increase in cell division (number)

14 Agrobacterium tumefaciens induces crown gall tumors by transferring T-DNA that codes for the synthesis of which plant hormones?

A. Brassinosteroids and Salicylic Acid
B. Auxin (IAA) and Cytokinin
C. Gibberellin and Ethylene
D. Ethylene and ABA

15 Which enzyme degrades the -1,4-glucosidic linkages in cellulose?

A. Cellulase
B. Amylase
C. Ligninase
D. Xylanase

16 Pathogens that kill host tissue in advance of penetration and live on the dead matter are known as:

A. Necrotrophs (Perthotrophs)
B. Symbionts
C. Endophytes
D. Biotrophs

17 The 'shot-hole' symptom in leaves involves the formation of an abscission layer, often triggered by the production of:

A. Ethylene
B. Gibberellins
C. Cytokinins
D. Polysaccharides

18 Which of the following is a definition of a Vivotoxin?

A. A toxin produced only in culture media.
B. A substance produced in the infected host which is not the pathogen itself but causes disease symptoms.
C. An enzyme involved in respiration.
D. A toxin that kills the pathogen.

19 T-toxin, produced by Bipolaris maydis race T, specifically affects maize plants with:

A. Normal cytoplasm
B. Resistant nuclear genes
C. Texas male-sterile cytoplasm (CMS-T)
D. High sugar content

20 Lignin, a complex polymer conferring rigidity to wood, is primarily degraded by which group of organisms?

A. Viruses
B. Nematodes
C. White rot fungi (Basidiomycetes)
D. Fastidious vascular bacteria

21 What is the role of Pectin Methyl Esterase (PME) in cell wall degradation?

A. It degrades the cellulose network.
B. It breaks the pectin chain into galacturonic acid.
C. It inhibits host defense enzymes.
D. It removes the methoxyl group () from pectin, producing pectic acid.

22 Which mechanism creates variability in bacteria through the uptake of naked DNA from the environment?

A. Transduction
B. Transformation
C. Conjugation
D. Transfection

23 The phenomenon of Saltation (or sectoral mutation) in fungal cultures refers to:

A. The sexual reproduction stage.
B. The complete death of the culture.
C. The appearance of sectors with distinct morphological characters due to mutation or heterokaryosis.
D. The production of liquid exudates.

24 Phaseolotoxin, produced by Pseudomonas syringae pv. phaseolicola, causes halo blight in beans by inhibiting:

A. ATP synthase
B. Ornithine carbamoyltransferase (OCT)
C. Photosynthesis
D. Cell wall synthesis

25 Fusicoccin, a toxin produced by Fusicoccum amygdali, affects plants by:

A. Blocking xylem vessels
B. Inhibiting protein synthesis
C. Degrading chlorophyll directly
D. Stimulating uncontrolled opening of stomata

26 What is the primary effect of Indole-3-Acetic Acid (IAA) when produced in excess by pathogens like Pseudomonas savastanoi?

A. Hyperplasia (gall formation)
B. Root rot
C. Dwarfing
D. Leaf abscission

27 Which of the following is NOT a cell wall degrading enzyme?

A. Cellulase
B. Protease
C. Hemicellulase
D. Pectinase

28 The 'Gene-for-Gene' hypothesis, explaining variability and host-pathogen interaction, was proposed by:

A. Robert Koch
B. Anton de Bary
C. H.H. Flor
D. E.J. Butler

29 HC-toxin affects maize by inhibiting which specific enzyme activity?

A. Glutamine synthetase
B. Plasma membrane ATPase
C. RNA polymerase
D. Histone deacetylase

30 Witches' broom symptoms are typically associated with an imbalance of which plant hormone?

A. Gibberellins
B. Ethylene
C. Abscisic Acid
D. Cytokinins

31 Which enzyme breaks down hemicellulose (e.g., xylan) in the plant cell wall?

A. Amylase
B. Cutinase
C. Xylanase
D. Lipase

32 In the context of bacterial variability, Conjugation requires:

A. Naked DNA in the solution
B. Formation of spores
C. Physical contact between two bacteria via a pilus
D. A bacteriophage vector

33 Phytotoxins that are not specific to a host and can affect a wide range of plants are termed:

A. Non-host-selective toxins
B. Host-selective toxins
C. Phytoalexins
D. Antibodies

34 Which molecule acts as the 'cement' holding plant cells together and is the first target of enzymatic attack by soft-rot pathogens?

A. Cellulose
B. Lignin
C. Suberin
D. Pectin

35 Abscisic Acid (ABA) generally promotes disease susceptibility by:

A. Killing the pathogen directly
B. Strengthening the cell wall
C. Suppressing defense responses like Salicylic Acid pathways
D. Increasing photosynthesis

36 Tentoxin, produced by Alternaria alternata, induces chlorosis by interfering with:

A. DNA replication
B. Water uptake
C. Chloroplast development and energy transfer
D. Cell division

37 The conversion of indole-3-acetamide (IAM) to indole-3-acetic acid (IAA) in bacteria like Pseudomonas savastanoi is catalyzed by:

A. Indoleacetamide hydrolase
B. Pectin lyase
C. Tryptophan monooxygenase
D. IAA hydrolase

38 What is the primary role of phospholipases in pathogenesis?

A. Degrading starch reserves
B. Degrading the cell wall
C. Degrading the plant cell membrane
D. Degrading the nucleus

39 Amylases are enzymes that degrade:

A. Nucleic acids
B. Lipids
C. Starch
D. Proteins

40 Root knot nematodes (Meloidogyne spp.) induce the formation of giant cells. This is an example of pathogen-induced changes in:

A. Growth regulators
B. Transpiration
C. Toxin levels
D. Lignification

41 Transduction as a mechanism of variability involves:

A. Transfer of DNA via a bacteriophage (virus)
B. Sexual fusion
C. Direct DNA uptake
D. Mutation by UV light

42 Which of the following is an example of a Hemibiotroph?

A. Botrytis cinerea (Strict Necrotroph)
B. Tobacco Mosaic Virus
C. Phytophthora infestans
D. Powdery Mildew fungi

43 The 'Epinasty' (downward bending of leaves) symptom seen in some wilt diseases is primarily caused by:

A. Excessive Ethylene
B. Deficiency of Cytokinin
C. Excessive Auxin
D. Lack of water

44 What is the function of Cutinases during the pre-penetration and penetration phase?

A. It creates a nutrient sink.
B. It masks the pathogen from the host immune system.
C. It hydrolyzes the lipid polyester cutin to allow hyphal entry.
D. It kills the epidermal cells.

45 Which enzyme splits pectin chains by 'elimination' (trans-elimination) rather than hydrolysis?

A. Polygalacturonase
B. Pectin Lyase (PL) / Pectate Lyase
C. Cellulase
D. Pectin Methyl Esterase

46 A pathogen strain that differs from others in pathogenicity (ability to infect specific host varieties) is called a:

A. Physiologic Race
B. Genus
C. Morphotype
D. Species

47 Which toxin causes 'fire blight' symptoms but is actually a virulence factor rather than a strict phytotoxin?

A. Amylovorin
B. T-toxin
C. HC-toxin
D. Victorin

48 In fungal pathogenesis, oxalic acid acts synergistically with which enzymes?

A. Nitrogenases
B. Pectinases
C. Proteases
D. Lipases

49 General resistance (Horizontal resistance) is usually effective against:

A. None of the above
B. All races of the pathogen
C. Only viruses
D. Only one specific race of the pathogen

50 The degradation of the secondary cell wall typically involves the breakdown of:

A. Only Pectin
B. Cellulose, Hemicellulose, and Lignin
C. Starch and Lipid
D. Cutin and Wax