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Chapter Analysis
Intermediate16 pages • EnglishQuick Summary
This chapter provides a fundamental understanding of plant growth and development, emphasizing the irreversible increase in size and differentiation into specialized structures. It explains the meristematic basis of plant growth, the phases of growth, and the role of plant growth regulators like auxins, gibberellins, cytokinins, abscisic acid, and ethylene in managing growth and development processes. The chapter also highlights the effect of intrinsic and extrinsic factors, such as light and temperature, on plant growth and developmental cycles.
Key Topics
- •Plant growth and development phases
- •Role of plant growth regulators
- •Differentiation, dedifferentiation, and redifferentiation
- •Effects of intrinsic and extrinsic factors on growth
- •Mechanisms of phototropism and geotropism
- •Plasticity and adaptability in plant development
- •Stress responses and adaptation
- •Plant hormone interactions
Learning Objectives
- ✓Describe the phases of plant growth and differentiate between them
- ✓Understand the role and types of plant growth regulators
- ✓Explain the concepts of differentiation, dedifferentiation, and redifferentiation
- ✓Identify how intrinsic and extrinsic factors affect plant growth
- ✓Analyze plant development in response to environmental cues
- ✓Recognize the significance of plasticity in plant growth and adaptation
Questions in Chapter
Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
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Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
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Describe briefly: (a) Arithmetic growth (b) Geometric growth (c) Sigmoid growth curve (d) Absolute and relative growth rates.
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List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applications of any one of them.
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Why is abscisic acid also known as stress hormone?
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‘Both growth and differentiation in higher plants are open’. Comment.
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‘Both a short day plant and a long day plant can produce can flower simultaneously in a given place’. Explain.
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Which one of the plant growth regulators would you use if you are asked to: (a) induce rooting in a twig (b) quickly ripen a fruit (c) delay leaf senescence (d) induce growth in axillary buds (e) ‘bolt’ a rosette plant (f) induce immediate stomatal closure in leaves.
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Would a defoliated plant respond to photoperiodic cycle? Why?
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What would be expected to happen if: (a) GA3 is applied to rice seedlings (b) dividing cells stop differentiating (c) a rotten fruit gets mixed with unripe fruits (d) you forget to add cytokinin to the culture medium.
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Additional Practice Questions
How does light affect the plant growth and development process?
mediumAnswer: Light influences photomorphogenesis, phototropism, and photosynthesis, which are vital in plant growth. It acts as a signal for germination, flowering, and setting circadian rhythms.
What role does temperature play in plant growth?
mediumAnswer: Temperature affects enzymatic activities, metabolic processes, and physiological functions; both high and low extremes can impede growth and development, leading to dormancy or stress.
Explain the concept of plasticity in plant development.
mediumAnswer: Plasticity refers to the ability of plants to adapt morphologically and physiologically to different environments or stages, like heterophylly in juvenile and mature plants under varying conditions.
Describe the process of dedifferentiation in plant cells.
hardAnswer: Dedifferentiation is the process wherein once differentiated cells regain the ability to divide and form meristems. This is a critical aspect of regeneration and wound healing in plants.
How are plant growth regulators used to control agricultural practices?
mediumAnswer: Auxins promote rooting; gibberellins enhance shoot length; cytokinins delay aging in produce; ethylene regulates fruit ripening; and abscisic acid manages stress responses.
Illustrate the difference between arithmetic and geometric growth with examples.
easyAnswer: In arithmetic growth, a cell divides, one daughter cell differentiates while the other continues to divide, e.g., root elongation. In geometric growth, both divide and grow exponentially, e.g., bacterial growth.
What is the significance of the sigmoid growth curve in plant biology?
easyAnswer: The sigmoid curve represents the typical growth pattern of organisms, highlighting phases of slow, rapid, and stable growth, showing the limits of growth and resource utilization over time.
Discuss the role of cellular differentiation in the development of plant structures.
hardAnswer: Differentiation involves structural and functional changes in cells, essential for forming specialized tissues like xylem and phloem, which support water transport and nutrient distribution.
Explain how auxin concentration affects plant growth direction.
mediumAnswer: Auxin distribution causes differential growth; high concentrations promote cell elongation on the shaded side, causing bends toward light (positive phototropism).
Why is abscisic acid referred to as the 'stress hormone' in plants?
mediumAnswer: Abscisic acid triggers stomatal closure to conserve water during drought and induces dormancy, providing resilience against environmental stressors.