Introduction to Plant Growth and Development

Plants show a remarkable capacity for growth throughout their life. Plant growth and development involve a coordinated series of physiological processes that result in an increase in size, complexity, and functional efficiency.

What is Growth?

Growth is defined as a permanent, irreversible increase in size, mass, volume, or number of cells of a living organism or its parts. Growth is always accompanied by metabolic activities and requires energy.

  • Growth is quantitative and measurable
  • Increase may be in length, area, volume, fresh weight, dry weight, or cell number

Plant Growth is Indeterminate

Unlike animals, plant growth is usually indeterminate, meaning it continues throughout life. This is because plants possess meristematic tissues that retain the ability to divide.

Meristems:

  • Apical Meristems (RAM & SAM): Responsible for primary growth (increase in length)
  • Lateral Meristems (Vascular cambium, Cork cambium): Responsible for secondary growth (increase in girth)

Continuous addition of new cells by meristems is called the open form of growth.

Growth is Measurable

Growth can be measured using:

  • Increase in cell number (e.g., root apical meristem)
  • Increase in length (pollen tube, stem)
  • Increase in area (leaf)
  • Increase in dry weight (most reliable)

Phases of Growth

Growth is a continuous process but is generally divided into three phases, which can be seen in a root tip:

  1. Phase of Meristematic Activity (Cell Division):
    • Occurs at the root and shoot apices.
    • Cells in this region are rich in protoplasm, have large nuclei, and thin, primary cell walls. They divide constantly.
  2. Phase of Elongation:
    • Located just proximal (behind) the meristematic zone.
    • Characterized by rapid cell enlargement, increased vacuolation, and new cell wall deposition. This phase is primarily responsible for the increase in length/height.
  3. Phase of Maturation:
    • Located proximal to the elongation phase.
    • Cells attain their maximal size and undergo protoplasmic and cell wall modifications to become specialized, mature cells (differentiation).

Growth Rates

Growth per unit time is called growth rate.There are 2 main types:

1. Arithmetic Growth

  • Only one daughter cell continues to divide
  • Growth increases at a constant rate
  • Linear growth pattern
  • Formula: Lₜ = L₀ + rt
  • Example: Elongation of a root at a constant rate.

2. Geometric Growth

  • Both daughter cells continue to divide
  • Shows exponential growth initially
  • Under natural conditions forms an S-shaped (sigmoid) curve

Sigmoid Curve Phases:

  • Lag phase → Log (exponential) phase → Stationary phase

  • Formula: W₁ = W₀eʳᵗ

Absolute vs Relative Growth Rate

  • Absolute Growth Rate (AGR): Total increase per unit time
  • Relative Growth Rate (RGR): Growth per unit initial size (efficiency index)

Conditions Required for Growth

  • Water: Cell enlargement and enzymatic reactions
  • Oxygen: Aerobic respiration for ATP
  • Nutrients: Synthesis of protoplasm
  • Optimum Temperature: Enzyme efficiency
  • Light & Gravity: Act as growth signals

Development in Plants

Development is the sum total of growth and differentiation. It includes qualitative changes that lead to maturation and functional specialisation.

Important Notes

  • Growth is irreversible and measurable
  • Development includes growth + differentiation
  • Maximum growth occurs in meristematic tissues

Memory Capsules – Growth at a Glance

ONE-LINE DEFINITIONS

  • Growth → Permanent, irreversible increase
  • Development → Growth + differentiation

MERISTEMS

  • Apical → Length (primary growth)
  • Lateral → Girth (secondary growth)

PHASES OF GROWTH (M-E-M):

  1. Meristematic
  2. Elongation
  3. Maturation

GROWTH TYPES

  • Arithmetic → Linear → One cell divides
  • Geometric → Exponential → Both cells divide

SIGMOID CURVE: Lag → Log → Stationary

FAVOURITE NEET LINE: Plant growth is indeterminate and shows open form of growth

💡 Questions and Answers

Q1. Define growth, meristem, and growth rate.

A1:

  • Growth: A permanent and irreversible increase in size, mass, or number of cells of a living organism.
  • Meristem: A region of actively dividing, undifferentiated cells responsible for continuous plant growth.
  • Growth Rate: Increase in growth per unit time.

Q2: Differentiate between arithmetic and geometric growth.

A2:

  • Arithmetic growth: One daughter cell divides, growth is linear and constant.
  • Geometric growth: Both daughter cells divide, growth is exponential and forms a sigmoid curve.

Q3: What is meant by open form of growth?

A3: Plants continuously produce new cells and organs throughout life due to persistent activity of apical meristems. This is called open form of growth.

Q4. Name and explain the three phases of growth in plants.

A4:

  1. Meristematic phase: Active cell division
  2. Elongation phase: Rapid cell enlargement
  3. Maturation phase: Cells differentiate into permanent tissues

Q5. What environmental factors are essential for plant growth?

A5: Water, oxygen, nutrients, optimum temperature, light, and gravity are essential for proper plant growth.