This set of Class 12 Biology Chapter 9 Multiple Choice Questions & Answers (MCQs) focuses on “Plant Diseases and their Control”.
1. Which of the following is not a method by which pathogens affect the yield of crops?
a) Reduce the quantity of yield
b) Reduce the quality of crop produce
c) Increase in cost production
d) Increase the flowering period
Explanation: Pathogens affect the crop yield by reducing the quantity of yield and reducing the quality of crop produce. Pathogens also increase the production cost due to reduced yield and expenditure on pesticides.
2. Which of the following is not a method of the perpetuation of disease by the pathogen?
a) The entry of pathogen through natural openings
b) Reproduction by pathogen
c) Reducing the quantity of yield
d) Direct penetration of the pathogen
Explanation: Various steps of the perpetuation of disease by the pathogen are coming of a pathogen in contact with host plants, entry of the pathogen into the host through natural openings, wounds or direct penetrations, the establishment of the pathogen inside the host, reproduction of pathogen, etc.
3. Which of the following is not a method of reducing total biomass of crop?
a) Damage to leaf tissues
b) Studying the crop
c) Killing branches
d) Stunting effect
Explanation: Diseases reduce the total biomass of the crop by causing damage to leaf tissues, stunting effect, damage to reproductive structures like flowers, fruits and seeds, killing of branches. This all results in the death of the plant.
4. Plant diseases are broadly classified into nonparasitic and parasitic.
Explanation: Plant diseases are broadly classified into two categories, nonparasitic and parasitic. Nonparasitic diseases are non-transmissible and are caused by physiological disorders due to defective heredity or unfavourable environment. Parasitic diseases are transmissible diseases which are caused by various categories of pathogens.
5. Which of the following is not related to Necrosis?
a) Curling of leaves
b) Death of tissues
c) A common symptom of fungal diseases
d) Discolouration of leaves
Explanation: Necrosis is the death of plant tissue or can be characterised by discolouration of areas on leaves, stems and roots. It is a common symptom in fungal diseases but also occurs in bacterial and viral diseases.
6. Necrosis cannot be in the form of _________
Explanation: Necrosis cannot be in the form of rots. It may be in the form of local lesions, cankers (necrotic lesions often sunken, exposing the interior), blights (burnt up appearance), scabs (roughened, crust-like lesions) and dieback (death and necrosis beginning form tip of branches towards the base).
7. Which of the following is not related to Rots?
a) Discolouration of tissue
b) Degeneration of succulent tissue
c) Distortion of leaves
d) It is of two types
Explanation: Rots is the discolouration, softening and degeneration of a succulent tissue due to fungal or bacterial infection. It is of two types- Dry rot (Rot is without an oozing) and Soft rot (Rot is accompanied by oozing).
8. Wilting is the loss of turgidity and drooping of leaves.
Explanation: Wilting is the loss of turgidity and drooping of leaves or shoots generally due to insufficiency of water. The pathogens usually block the vascular tissue for bringing wilt. It occurs in response to both bacterial and fungal infections.
9. Which of the following is not true regarding Chlorosis?
a) Yellowing of leaves
b) Death of plant tissues
c) Non-formation of chlorophyll
d) Destruction of chlorophyll
Explanation: Chlorosis is the yellowing of green tissues or structures (especially leaves) due to either non-formation or destruction of chlorophyll. Chlorosis is quite common in the case of mineral deficiency. It also occurs in response to fungal, bacterial and viral infections.
10. Which of the following is not a common symptom of plant disease?
b) Leaf curls
c) Perfect flowering
Explanation: The common symptoms of plant diseases include Necrosis, Pustules, Pitting, Rots, Leaf curls, Excessive growth of tissues, Stunting, Chlorosis, Wilting, Mosaics, Root Galls, Damping-off and excessive root branching.
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