Plant Growth and Development - Comprehensive NEET Biology Notes

1. Introduction to Plant Growth and Development

Plant growth and development encompass a series of processes that lead to the formation, maturation, and senescence of different plant organs such as roots, stems, leaves, flowers, and seeds. These processes are regulated by both intrinsic factors (like genetic and hormonal signals) and extrinsic factors (such as light, temperature, and nutrients). Understanding these processes is essential for NEET, as plant growth regulators and growth phases frequently appear in the exam.

Did You Know?

A plant’s ability to continue growing throughout its life is due to the presence of meristems, regions of active cell division that contribute to the plant's growth.

2. Plant Growth

2.1 Definition of Growth

Growth in plants is defined as an irreversible increase in size, which could be in terms of length, area, or volume. This process occurs at the cellular level and is accompanied by metabolic activities. Growth in plants can be either determinate or indeterminate.

NEET Tip:

Focus on the concept of indeterminate growth in plants and the role of meristems, as these topics are frequently tested.

Visual Aid Suggestion:

Diagrams showing different meristematic regions such as the root and shoot apical meristems will help clarify the concept of growth in plants.

2.2 Phases of Growth

Plant growth can be divided into three phases:

  • Meristematic Phase: This is the phase where active cell division occurs in the apical meristems of roots and shoots.
  • Elongation Phase: The newly formed cells increase in size, accompanied by increased vacuolation and deposition of new cell wall materials.
  • Maturation Phase: Cells differentiate and mature, acquiring their final structure and function.

Real-life Application:

Understanding growth phases is crucial in horticulture, where manipulating the growth phase can influence crop yield and plant structure.

Visual Aid Suggestion:

A diagram of the root tip showing the zones of meristematic activity, elongation, and maturation can provide a clear visual representation of the phases of growth.

Quick Recap

  • Growth in plants is an irreversible increase in size and is indeterminate due to meristem activity.
  • Plant growth occurs in three phases: meristematic, elongation, and maturation.
  • Meristems, particularly the root and shoot apical meristems, are responsible for continuous plant growth.

3. Differentiation, Dedifferentiation, and Redifferentiation

3.1 Differentiation

Differentiation is the process by which cells derived from meristems undergo structural and functional specialization to form various tissues and organs. For example, tracheary elements develop thick lignified cell walls to transport water efficiently.

NEET Problem-Solving Strategy:

Understand the process of differentiation, especially how it relates to the formation of specialized tissues like xylem and phloem, as this is frequently tested in NEET.

Visual Aid Suggestion:

A flowchart showing the differentiation of meristematic cells into various specialized tissues can help students understand this process.

3.2 Dedifferentiation and Redifferentiation

Dedifferentiation is the process by which mature, differentiated cells regain their ability to divide. This happens in the formation of tissues like cambium during secondary growth. Redifferentiation refers to the maturation of dedifferentiated cells into new specialized tissues.

Common Misconception:

Dedifferentiation does not mean the reversal of all cellular functions. It only allows cells to regain the ability to divide and form new tissues, not necessarily to revert to their original undifferentiated state.

Visual Aid Suggestion:

A diagram showing the process of dedifferentiation and redifferentiation in a woody dicot plant during secondary growth can clarify these concepts.

Quick Recap

  • Differentiation leads to the formation of specialized tissues from meristematic cells.
  • Dedifferentiation is the regaining of the ability to divide, while redifferentiation is the maturation of these cells into new tissues.
  • These processes are crucial for plant growth and adaptation.

4. Plant Growth Regulators (PGRs)

4.1 Characteristics and Types of PGRs

Plant growth regulators (PGRs) are small molecules that influence growth and development. These can be grouped into:

  • Growth Promoters: Auxins, gibberellins, and cytokinins.
  • Growth Inhibitors: Abscisic acid (ABA) and ethylene.

NEET Tip:

Pay attention to the different functions of PGRs, especially how auxins promote apical dominance and ethylene promotes fruit ripening, as these are common NEET topics.

Visual Aid Suggestion:

A table listing the major PGRs along with their functions and effects on plants can help with quick revision.

4.2 Physiological Effects of PGRs

  • Auxins: Promote cell elongation, apical dominance, rooting, and fruit development. They are also used in agricultural practices to induce parthenocarpy and as herbicides.
  • Gibberellins: Stimulate stem elongation, fruit growth, and seed germination. They are used in agriculture to enhance crop yield, particularly in sugarcane and grapes.
  • Cytokinins: Promote cell division, delay senescence, and overcome apical dominance.
  • Abscisic Acid (ABA): Inhibits growth, induces seed dormancy, and promotes stomatal closure during water stress, making it known as the stress hormone.
  • Ethylene: Promotes fruit ripening, seed germination, and flower wilting. It is widely used in agriculture to control the ripening of fruits like tomatoes and bananas.

Real-life Application:

PGRs are extensively used in agriculture to enhance crop production, control plant growth, and manage post-harvest ripening.

Visual Aid Suggestion:

Diagrams showing the effects of auxins on apical dominance or ethylene on fruit ripening can illustrate how these hormones function in real-world applications.

Quick Recap

  • PGRs are classified into growth promoters (auxins, gibberellins, cytokinins) and inhibitors (ABA, ethylene).
  • These regulators control various aspects of plant growth, development, and responses to environmental stress.
  • Understanding the roles and applications of PGRs is essential for NEET preparation.

5. Photoperiodism and Vernalization

5.1 Photoperiodism

Photoperiodism is the response of plants to the relative lengths of day and night. This affects processes such as flowering, with plants classified as short-day, long-day, or day-neutral based on their flowering responses to the length of daylight.

NEET Tip:

Focus on the critical day length and the role of phytochromes in photoperiodism, as questions on these topics are frequent in NEET.

Visual Aid Suggestion:

A graph illustrating the response of short-day and long-day plants to varying day lengths can help clarify the concept.

5.2 Vernalization

Vernalization is the induction of flowering by exposing plants to prolonged cold temperatures. This process is essential for biennials like carrots and beets, which require a period of cold before they can flower and produce seeds.

Real-life Application:

Vernalization is used in agriculture to manipulate the flowering time of crops, ensuring better yields in different climates.

Visual Aid Suggestion:

A diagram showing the stages of vernalization and its impact on flowering can aid in understanding this concept.

Quick Recap

  • Photoperiodism controls flowering in response to day length, with plants classified as short-day, long-day, or day-neutral.
  • Vernalization induces flowering through exposure to cold temperatures, influencing the lifecycle of many biennial plants.
  • Understanding these phenomena is crucial for manipulating crop growth and yield.

NEET Exam Strategy

  • Focus on understanding plant growth phases, differentiation, and the roles of various PGRs.
  • Practice diagram-based questions, especially those involving photoperiodism and the effects of PGRs on plant development.
  • Be clear on the processes of dedifferentiation and redifferentiation, as they are essential for tissue culture applications.

Practice Questions

  1. Which of the following plant hormones promotes apical dominance?
    Solution: b) Auxins
    • a) Cytokinins
    • b) Auxins
    • c) Gibberellins
    • d) Ethylene
  3. What is the role of abscisic acid in plants?
    Solution: b) Induces seed dormancy and closes stomata
    • a) Promotes fruit ripening
    • b) Induces seed dormancy and closes stomata
    • c) Stimulates cell division
    • d) Promotes stem elongation
  5. Which hormone is known as the stress hormone in plants?
    Solution: d) Abscisic acid
    • a) Ethylene
    • b) Gibberellin
    • c) Auxin
    • d) Abscisic acid
  7. What is vernalization?
    Solution: a) Inducing flowering by exposure to cold
    • a) Inducing flowering by exposure to cold
    • b) Promoting seed germination
    • c) Increasing leaf size
    • d) Stimulating root formation
  9. Which plant growth regulator is used to ripen fruits like tomatoes and bananas?
    Solution: b) Ethylene
    • a) Auxin
    • b) Ethylene
    • c) Gibberellin
    • d) Abscisic acid

Glossary

  • Meristem: Region of active cell division in plants responsible for growth.
  • Differentiation: The process of cells becoming specialized in structure and function.
  • Dedifferentiation: The ability of mature cells to regain the capacity to divide.
  • Photoperiodism: The response of plants to the length of day and night.
  • Vernalization: The induction of flowering by prolonged exposure to cold temperatures.