Class 11 Biology - ISC
Plant Growth and Development
The chapter 'Plant Growth and Development' in Class 11 ISC Biology explores the irreversible increase in size, shape, and form of plants, alongside the structural changes they undergo from seed germination to senescence. Students will study indeterminate growth, the phases of growth, and the crucial role played by plant growth regulators (PGRs) such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid. Additionally, the chapter covers photoperiodism and vernalization, which control flowering. For ISC board exams, this is a high-scoring physiological chapter where direct questions on PGR functions, graphs of geometric growth, and differences between plant hormones frequently appear.
Start Learning FreeKey Concepts
Plant Growth and Indeterminate Growth
Plant growth is generally indeterminate because plants retain meristems throughout their life that have the capacity for continuous cell division and elongation.
Phases of Growth
The three main phases of growth are meristematic (constant division), elongation (increased vacuolation and cell expansion), and maturation (cell differentiation and maximum size).
Geometric Growth Rate
In geometric growth, following mitotic cell division, only one daughter cell continues to divide while the other differentiates, yielding an S-shaped (sigmoid) growth curve represented by W1 = W0 * e^(rt).
Plant Growth Regulators (PGRs)
PGRs are small, simple molecules of diverse chemical composition that act as chemical messengers, categorized into promoters (auxins, gibberellins, cytokinins) and inhibitors (abscisic acid, ethylene).
Photoperiodism
Photoperiodism is the physiological response of plants to the relative lengths of light and dark periods (photoperiods) which dictates the timing of flowering.
Vernalization
Vernalization is the dependence of flowering either quantitatively or qualitatively on exposure to a low temperature period, preventing premature reproductive development in winter.
Important Formulas
Board Exam Info
In the ISC Class 11 Biology theory paper, this chapter typically carries around 5 to 7 marks. Common question types include direct short-answer questions on the physiological effects of specific plant hormones (e.g., role of ethylene in fruit ripening or gibberellins in bolting), graph-based questions on arithmetic and geometric growth curves, and distinctions between short-day and long-day plants.
Frequently Asked Questions
What is the difference between arithmetic and geometric growth?
In arithmetic growth, only one daughter cell continues to divide while the other differentiates, leading to a linear growth curve. In geometric growth, both daughter cells remain mitotic, resulting in an exponential increase and an S-shaped sigmoid curve.
How do auxins and cytokinins regulate morphogenesis in plant tissue culture?
A high auxin-to-cytokinin ratio promotes root differentiation, whereas a high cytokinin-to-auxin ratio promotes shoot regeneration. A balanced ratio typically stimulates callus formation.
What triggers bolting in rosette plants?
Bolting, which is the internode elongation just prior to flowering in rosette plants like beet and cabbage, is primarily induced by the application of gibberellins.
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