Chapter 15: Plant Growth and Development – Study Modules with Revision Notes
CBSE Class 11 Biology Study Module – Plant Growth and Development (NCERT Based)
Course: CBSE Class 11 Biology
Unit IV: Plant Physiology
Chapter 15: Plant Growth and Development
Board: CBSE (Central Board of Secondary Education)
Examination Level: CBSE Class 11 – Annual Examination
Curriculum: Strictly as per NCERT Biology Textbook
CBSE Class 11 Biology Chapter 15 – Plant Growth and Development | NCERT-Based Study Module & Revision Notes
Introduction to Plant Growth and Development
Plant Growth and Development is a fundamental chapter under Unit IV: Plant Physiology, focusing on how plants grow, differentiate, and respond to internal and external signals. This chapter forms the conceptual base for understanding plant life cycles, agricultural productivity, and physiological adaptations.
The chapter integrates growth processes, cellular differentiation, plant hormones (phytohormones), and environmentally regulated phenomena such as photoperiodism and vernalisation. Questions from this chapter are frequently asked in CBSE Class 11 examinations and also serve as groundwork for competitive exams like NEET.
Section 1: Growth in Plants
1.1 Definition of Growth
Growth is defined as a permanent, irreversible increase in size, mass, volume, or number of cells of an organism. In plants, growth is usually indeterminate, meaning it continues throughout life due to the presence of meristematic tissues.
Key Characteristics of Plant Growth
- Permanent and irreversible
- Involves increase in cell number and cell size
- Energy-dependent process
- Regulated genetically and environmentally
1.2 Phases of Growth
Plant growth occurs in three sequential phases:
a) Meristematic Phase
- Cells actively divide
- Thin cell walls
- Dense cytoplasm and large nucleus
- Found at root and shoot apices
b) Elongation Phase
- Cells increase in size
- Cell walls loosen and stretch
- Vacuole enlarges
- Maximum growth rate observed
c) Maturation Phase
- Cells differentiate and attain permanent shape and function
- Growth rate slows down
- Cells become specialized
1.3 Growth Rate
Growth rate refers to the increase in growth per unit time and can be expressed as:
- Arithmetic Growth: Increase by a constant amount
- Geometric Growth: Increase by a constant proportion
Growth is influenced by:
- Genetic factors
- Availability of nutrients
- Environmental conditions
- Plant hormones
1.4 Conditions Necessary for Growth
For optimal growth, plants require:
- Water: Maintains turgidity and facilitates metabolic reactions
- Oxygen: Needed for respiration
- Nutrients: Essential for biosynthesis
- Temperature: Affects enzyme activity
- Light: Indirectly influences growth through photosynthesis
Section 2: Differentiation, Dedifferentiation, and Redifferentiation
2.1 Differentiation
Differentiation is the process by which cells develop specific structural and functional characteristics. It involves changes in:
- Cell structure
- Metabolic activity
- Gene expression
Example: Formation of xylem and phloem from meristematic cells.
2.2 Dedifferentiation
Dedifferentiation is the process by which mature, differentiated cells regain the capacity to divide.
Example:
- Formation of cork cambium from cortical cells
- Formation of interfascicular cambium
2.3 Redifferentiation
Redifferentiation refers to the process where dedifferentiated cells lose their capacity to divide and specialize again.
Together, these processes highlight the plasticity of plant growth, allowing plants to adapt to changing environments.
Section 3: Development in Plants
3.1 Concept of Development
Development is the sum total of growth and differentiation. It includes:
- Seed germination
- Vegetative growth
- Flowering
- Senescence
Development is controlled by:
- Internal factors (hormones, genes)
- External factors (light, temperature)
Section 4: Plant Hormones (Phytohormones)
Plant hormones are small organic substances synthesized in one part of the plant and transported to another part, where they influence physiological processes.
Classification of Plant Hormones
- Auxins
- Gibberellins
- Cytokinins
- Ethylene
- Abscisic Acid (ABA)
4.1 Auxins
Examples: IAA (Indole-3-acetic acid)
Functions:
- Promote cell elongation
- Apical dominance
- Root initiation
- Delay leaf abscission
- Tropic responses
Auxins are widely used in agriculture and horticulture.
4.2 Gibberellins
Examples: GA₃
Functions:
- Stem elongation
- Bolting in rosette plants
- Seed germination
- Induction of flowering
- Breaking dormancy
4.3 Cytokinins
Examples: Kinetin, Zeatin
Functions:
- Promote cell division
- Delay senescence
- Promote lateral bud growth
- Mobilization of nutrients
4.4 Ethylene
Ethylene is the only gaseous plant hormone.
Functions:
- Fruit ripening
- Senescence
- Leaf abscission
- Breaks dormancy in seeds
Ethylene shows triple response in seedlings:
- Reduced elongation
- Swelling of hypocotyl
- Horizontal growth
4.5 Abscisic Acid (ABA)
Also known as stress hormone.
Functions:
- Inhibits growth
- Induces dormancy
- Promotes stomatal closure during water stress
- Accelerates senescence
Section 5: Photoperiodism
5.1 Definition
Photoperiodism is the response of plants to the relative lengths of day and night, especially in relation to flowering.
5.2 Types of Plants Based on Photoperiodism
a) Short-Day Plants
- Flower when day length is shorter than critical duration
- Example: Rice, Chrysanthemum
b) Long-Day Plants
- Flower when day length exceeds critical duration
- Example: Wheat, Spinach
c) Day-Neutral Plants
- Flowering independent of day length
- Example: Tomato, Cotton
5.3 Role of Phytochrome
Phytochrome is a photoreceptor pigment that exists in two forms:
- Pr (inactive)
- Pfr (active)
It plays a crucial role in regulating flowering and other light-mediated responses.
Section 6: Vernalisation
6.1 Definition
Vernalisation is the requirement of a low-temperature exposure to stimulate flowering in some plants.
6.2 Significance of Vernalisation
- Shortens vegetative phase
- Promotes early flowering
- Ensures flowering occurs in favorable seasons
- Important in biennial and winter annual plants
6.3 Devernalisation
The reversal of vernalisation effect by exposure to high temperature is known as devernalisation.
Section 7: Revision Notes – Key Exam Points
Important Definitions
- Growth: Permanent increase in size
- Differentiation: Specialization of cells
- Development: Growth + differentiation
- Photoperiodism: Response to day length
- Vernalisation: Cold-induced flowering
Key Differences to Remember
- Arithmetic vs Geometric growth
- Short-day vs Long-day plants
- Growth promoters vs Growth inhibitors
NCERT-Based Exam Tips
- Diagrams are frequently asked from growth phases
- Hormone functions are important for short answers
- Photoperiodism and vernalisation often appear as conceptual questions
- Focus on definitions and examples as given in NCERT
Conclusion
The chapter Plant Growth and Development provides a holistic understanding of how plants grow, differentiate, and respond to environmental and hormonal cues. Mastery of this chapter is essential not only for CBSE Class 11 examinations but also for advanced studies in plant physiology, agriculture, and biotechnology.
A thorough revision of concepts, definitions, and physiological roles of plant hormones, along with clear understanding of photoperiodism and vernalisation, will ensure strong performance in examinations.