Questions
~2 questions per exam
Difficulty
Easy
Importance
Low yield — focus on hormone functions
Overview
Plant Growth and Development covers the physiological and chemical processes governing how plants increase in size and adapt to their environment. It is a fundamental unit in the Class 11 biology curriculum that focuses on hormonal regulation and environmental signaling. Mastering this topic requires memorizing the specific roles of plant growth regulators (PGRs) and their physiological effects.
Growth Phases
Plant growth is an irreversible increase in mass and size, occurring in distinct phases: meristematic, elongation, and maturation. Understanding these phases is crucial as they represent the cellular basis of primary and secondary growth.
- Meristematic phase: Constant cell division in root and shoot apices
- Elongation phase: Increased vacuolation and cell enlargement
- Maturation phase: Cell differentiation and specialization
- Arithmetic growth: Linear growth (L_t = L_0 + rt)
- Geometric growth: Exponential growth (W_1 = W_0 * e^{rt})
Plant Growth Regulators (PGRs)
PGRs are small, simple chemical compounds that act as master regulators of plant development. Exam questions typically focus on distinguishing between growth promoters like auxins/gibberellins and growth inhibitors like abscisic acid.
- Auxins: Apical dominance and cell elongation
- Gibberellins: Bolting effect and seed germination
- Cytokinins: Cell division and delaying senescence
- Ethylene: Fruit ripening and horizontal seedling growth
- Abscisic Acid (ABA): Stress hormone and seed dormancy induction
Photoperiodism
Photoperiodism refers to the plant's physiological response to relative lengths of day and night. This mechanism regulates flowering, categorized into short-day, long-day, and day-neutral plants based on the critical dark period.
- Phytochrome: Pigment responsible for light perception
- Short-day plants: Flower only when the night is longer than critical length
- Long-day plants: Flower only when the night is shorter than critical length
- Vernalization: Low temperature promotion of flowering
- Critical dark period is the actual trigger for flowering
Formula Sheet
Arithmetic Growth: L_t = L_0 + rt
Geometric Growth: W_1 = W_0 * e^{rt}
Exam Tip
Create a comparison table for the five major plant hormones focusing solely on their primary physiological 'trigger' effect to avoid confusion during rapid revision.
Common Mistakes
- Confusing the specific roles of Gibberellins (bolting) versus Auxins (apical dominance).
- Misinterpreting the photoperiodic response by focusing on the day length rather than the critical dark period.
- Forgetting that ABA acts as a growth inhibitor rather than a promoter.
More Revision Notes
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