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Q3:
Name important defence mechanisms in plants against herbivory.
Solution :
1. Theoretical Framework of Plant Defense Mechanisms
Plants are sessile organisms and cannot escape predation. Consequently, they have evolved a sophisticated array of morphological, chemical, and behavioral defense mechanisms to minimize damage from herbivores. These adaptations are governed by the principle of co-evolution, where the herbivore's ability to feed forces the plant to develop more effective deterrents [Per the Arms-Race Hypothesis].
2. Morphological Defense Mechanisms
These are physical barriers that obstruct the herbivore's ability to consume plant tissues.
- Thorns and Spines: Modified stems (thorns) or leaves (spines) provide mechanical resistance against large mammalian herbivores. Example: Acacia and Cactus.
- Trichomes: Fine hair-like outgrowths on the epidermis can trap insects or provide a distasteful surface.
- Silica Deposition: Some grasses incorporate silica into their cell walls, making the tissue abrasive and difficult to digest, effectively wearing down the teeth of grazers.
3. Chemical Defense Mechanisms
Plants produce a diverse repertoire of secondary metabolites that act as toxins, inhibitors, or deterrents [Per the Chemical Ecology Theory].
| Chemical Class | Mechanism of Action | Example |
|---|---|---|
| Cardiac Glycosides | Interferes with cardiac muscle function in vertebrates. | Calotropis |
| Alkaloids | Toxic to nervous systems; acts as a bitter deterrent. | Nicotine, Caffeine, Quinine |
| Tannins | Reduces protein digestibility, inhibiting herbivore growth. | Oak leaves, Tea |
| Terpenoids | Can act as volatile signals for predators of herbivores. | Essential oils in Lamiaceae |
4. Indirect Defense via Tritrophic Interactions
Plants often recruit the "enemies of their enemies." When damaged by an herbivore, the plant releases Volatile Organic Compounds (VOCs). These compounds act as chemical signals to attract predatory wasps or parasitic insects that hunt the herbivores, thereby reducing the herbivore population density.
5. Illustrative Schematic: Plant Defense Strategy
Final Solution: The defense mechanisms in plants against herbivory include morphological adaptations such as the presence of thorns, spines, and trichomes that physically hinder ingestion; chemical defenses involving the production of secondary metabolites like cardiac glycosides, alkaloids, and tannins that poison or deter herbivores; and indirect defenses involving the release of volatile compounds to recruit predators or parasitoids of the attacking herbivores.
More Questions from Class 12 Biology Organisms and Populations EXERCISES
- Q1: List the attributes that populations possess but not individuals.
- Q1: List the attributes that populations possess but not individuals.
- Q2: If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (\(r\)) of the population?
- Q2: If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase ((r)) of the population?
- Q3: Name important defence mechanisms in plants against herbivory.
- Q4: An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
- Q4: An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
- Q5: What is the ecological principle behind the biological control method of managing with pest insects?
- Q5: What is the ecological principle behind the biological control method of managing with pest insects?
- Q6: Define population and community.
- Q6: Define population and community.
- Q7(a): Define the following terms and give one example for each: (a) Commensalism
- Q7(a): Define the following term and give one example for it: Commensalism
- Q7(b): Define the following terms and give one example for each: (b) Parasitism
- Q7(b): Define the following term and give one example for it: Parasitism
- Q7(c): Define the following terms and give one example for each: (c) Camouflage
- Q7(c): Define the following term and give one example for it: Camouflage
- Q7(d): Define the following terms and give one example for each: (d) Mutualism
- Q7(d): Define the following term and give one example for it: Mutualism
- Q7(e): Define the following terms and give one example for each: (e) Interspecific competition
- Q7(e): Define the following term and give one example for it: Interspecific competition
- Q8: With the help of suitable diagram describe the logistic population growth curve.
- Q8: With the help of suitable diagram describe the logistic population growth curve.
- Q9: Select the statement which explains best parasitism.
- Q9: Select the statement which explains best parasitism.
- Q10: List any three important characteristics of a population and explain.
- Q10: List any three important characteristics of a population and explain.
CBSE Solutions for Class 12 Biology Organisms and Populations
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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