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Comprehensive Guide to Class 11 NCERT Biology Chapter – Plant Growth and Development Explained with Phases, Hormones, and Environmental Factors


🌱 Class 11 Biology: Plant Growth and Development – NCERT Chapter Explained


Category: Class 11 Biology | Chapter: Plant Growth and Development | Board: CBSE/NCERT



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Understanding how plants grow and develop is essential to appreciate their complex life processes. In Class 11 NCERT Biology, the chapter "Plant Growth and Development" gives us a deep insight into how a tiny seed transforms into a giant tree, guided by hormones and environmental cues. Let’s break down this chapter into simple sections for easy understanding.



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📌 Chapter Overview


Plants, though stationary, show dynamic changes throughout their life. These changes include:


Growth (increase in size or mass)


Development (differentiation and maturation of tissues)


Differentiation (specialization of cells for specific functions)



The chapter focuses on:


Characteristics and phases of growth


Growth rate and conditions for growth


Plant hormones or phytohormones


Seed dormancy and germination


Photoperiodism and vernalisation




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🌿 1. What is Plant Growth?


✳️ Definition:


Growth is defined as an irreversible permanent increase in size, volume, or number of cells.


✳️ Characteristics:


Irreversible (cannot be undone)


Measurable (e.g., increase in height, number of leaves)


Occurs throughout life in plants (due to presence of meristems)




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🔄 2. Phases of Growth


There are three phases:


1. Meristematic Phase:


Cells divide actively


Occurs at root and shoot tips (apical meristems)




2. Elongation Phase:


Cells increase in size


Located just behind the meristematic region




3. Maturation Phase:


Cells attain maturity and perform specific functions






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📈 3. Growth Rate


Growth can be:


✳️ Arithmetic Growth:


One cell divides to form two; one remains active, the other differentiates


Linear growth over time


Formula:



L_t = L_0 + rt


✳️ Geometric Growth:


Both daughter cells continue dividing


Exponential growth (seen in early stages)




✳️ Sigmoid Growth Curve (S-shaped):



Lag phase → Log phase → Steady state


Common in living organisms




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☀️ 4. Conditions for Growth


Growth in plants depends on:


Water – for cell expansion and enzyme activity


Oxygen – for respiration


Nutrients – essential for building tissues


Light & Temperature – affect photosynthesis, metabolism




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🔬 5. Differentiation, Dedifferentiation & Redifferentiation


Differentiation: Cells become specialized (e.g., xylem cells)


Dedifferentiation: Specialized cells become meristematic again (e.g., interfascicular cambium)


Redifferentiation: Dedifferentiated cells specialize again



👉 Unique to plants – shows high flexibility and regeneration capacity



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🌱 6. Development


Plant development is the sum total of growth and differentiation, guided by:


Internal factors: Hormones, genes


External factors: Light, temperature, gravity




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🌿 7. Plant Growth Regulators (Hormones)


Plants produce specific hormones to control growth and development. These are grouped into five major types:


✳️ 1. Auxins:


Stimulate cell elongation, root initiation


Delay leaf abscission


E.g., IAA (Indole-3-acetic acid), NAA



✳️ 2. Gibberellins (GA):


Promote stem elongation, seed germination


Break seed dormancy


Cause bolting in rosette plants



✳️ 3. Cytokinins:


Promote cell division


Delay senescence (aging)


Found in actively dividing tissues (e.g., roots, fruits)



✳️ 4. Abscisic Acid (ABA):


Growth inhibitor


Promotes dormancy and closing of stomata


Called stress hormone



✳️ 5. Ethylene:


Gaseous hormone


Promotes fruit ripening, leaf abscission


Also helps in root hair formation




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🌼 8. Photoperiodism


Plants respond to the duration of light and dark in a day.


Types of Plants Based on Photoperiod:


Short Day Plants – Flower when day < critical length (e.g., rice, soybean)


Long Day Plants – Flower when day > critical length (e.g., wheat, spinach)


Day Neutral Plants – Independent of light duration (e.g., tomato, cotton)



🔦 Phytochrome – a pigment that detects light/dark changes



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❄️ 9. Vernalisation


It is the induction of flowering by exposure to low temperature.


Helps temperate plants to flower in spring after winter


Example: Wheat, Barley, Carrot




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🌾 10. Seed Dormancy and Germination


Dormancy: Period when seeds do not germinate even in favorable conditions


Causes: Hormonal imbalance, seed coat hardness, immature embryo


Breaking Dormancy:


Exposure to chilling


Mechanical/chemical scarification


Treatment with gibberellins



Germination: Resumption of growth in a seed under favorable conditions




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📚 Conclusion


The chapter "Plant Growth and Development" shows that plant growth is much more than just an increase in size. It is a carefully regulated, hormone-guided journey from a seed to a fully developed plant, reacting to its environment. Understanding this helps in agriculture, horticulture, and even biotechnology.



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✍️ Keywords for Revision:


Meristem


Differentiation


Auxin, Gibberellin


ABA, Ethylene


Photoperiodism


Vernalisation


Dormancy




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✅ Tip for Students

: Prepare diagrams like the sigmoid growth curve, hormonal effects, and seed germination stages to strengthen your understanding and exam performance.


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