Class 11 Biology - PUNJAB
Plant Growth and Development
The chapter 'Plant Growth and Development' in Class 11 Biology explores the fascinating processes by which plants grow, differentiate, and respond to internal and environmental signals. Students will learn about indeterminate growth, phases of plant growth, and mathematical expressions of growth rate. A major focus is dedicated to plant growth regulators (PGRs) such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid, which act as chemical messengers. Additionally, the chapter covers photoperiodism and vernalization, explaining how light and temperature control flowering. Mastering this chapter is essential for PSEB board exams as it features both conceptual questions and direct role-based questions on plant hormones.
Start Learning FreeKey Concepts
Plant Growth
An irreversible, permanent increase in size, dry weight, or volume of an organism, driven primarily by cell division, elongation, and differentiation.
Arithmetic and Geometric Growth
In arithmetic growth, only one daughter cell continues to divide while the other differentiates, yielding a linear growth curve (L_t = L_0 + rt). In geometric growth, both daughter cells divide, resulting in an exponential curve (W_1 = W_0 e^{rt}).
Plant Growth Regulators (PGRs)
Small, simple organic molecules of diverse chemical composition that act as plant hormones (auxins, gibberellins, cytokinins, ethylene, and ABA) to promote or inhibit growth and development.
Photoperiodism
The physiological response of plants to the relative lengths of light and dark periods (day length) which critically regulates flowering in short-day, long-day, and day-neutral plants.
Vernalization
The phenomenon where flowering is either promoted or dependent on exposure to a prolonged period of low (chilling) temperatures, commonly seen in winter varieties of crops.
Important Formulas
Board Exam Info
In the Punjab (PSEB) Class 11 Biology board examinations, this chapter typically carries around 4 to 6 marks. Questions usually include short-answer questions on the physiological effects of plant growth hormones, differentiations between arithmetic and geometric growth, and conceptual questions on photoperiodism and vernalization.
Frequently Asked Questions
What is the difference between differentiation, dedifferentiation, and redifferentiation?
Differentiation is when cells attain a mature, permanent function. Dedifferentiation is the reversion of mature cells to form a meristematic tissue (e.g., interfascicular cambium). Redifferentiation is when these dedifferentiated cells lose their capacity to divide again and mature to perform specific functions.
Which plant hormone is known as the 'stress hormone'?
Abscisic Acid (ABA) is known as the stress hormone because its production is stimulated by various kinds of stress, especially water stress, causing stomatal closure and seed dormancy.
Why is ethylene considered unique among plant growth regulators?
Ethylene is unique because it is a simple gaseous hormone. It is synthesized in large amounts by ripening fruits and tissues undergoing senescence, and it promotes horizontal growth and apical hook formation in dicot seedlings.
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