🌱 Lesson 8.7 – Growth in Plants

📌 Introduction to Plant Growth

🌿 What is Plant Growth?

Growth in plants means a permanent and irreversible increase in size. Once a plant grows, it doesn’t shrink back. This increase in size can happen in:

  • Height (a tree growing taller),
  • Width (a stem becoming thicker),
  • Mass (the plant gaining weight due to more cells).

🌱 Growth by Addition of Organs

Plants don’t just grow bigger in one way. They continuously produce new parts like:

  • Branches (that spread out),
  • Leaves (that help in photosynthesis),
  • Roots (that anchor the plant and absorb water).

Think of a growing plant like a construction site—new rooms (organs) are constantly being built.

🔬 Growth Is Not Equal in All Parts

Growth in a plant does not happen everywhere at the same time. It depends on the type of plant:

  • In lower plants (like algae or moss), the whole body can grow.
  • In higher plants (like flowering plants and trees), only specific areas grow. These areas are known as:

🔬 Meristems – The Growing Regions

Meristems are special groups of cells in a plant that keep dividing. These cells are like stem cells in animals—they can produce new types of cells for different plant parts.

🔍 Types of Meristems

There are three main types of meristems depending on where they are located and what role they play.

1. Apical Meristems

  • Location: At the tips of roots and shoots.
  • Function: Help the plant grow taller and deeper.
  • This is called primary growth because it is the first or main type of growth in a plant.

Example: When a sunflower grows taller every day, it is due to apical meristems.

2. Intercalary Meristems

  • Location: At the base of leaves or internodes (the space between two leaves or branches).
  • Found in: Grasses and some herbaceous plants.
  • These meristems help in regrowth of parts like leaves or stem.

Example: When you cut grass and it regrows quickly, it is because of the intercalary meristems.

3. Lateral Meristems

  • Location: Along the sides of stems and roots (like a cylinder).
  • Function: Help the plant grow wider or thicker.
  • This is called secondary growth.

There are two types of lateral meristems:

  • Vascular Cambium:
    • Found between xylem and phloem (the transport tissues).
    • Produces secondary xylem (wood) and secondary phloem.
  • Cork Cambium:
    • Found near the outer layers.
    • Produces cork cells which become part of the bark.

Example: When a tree trunk becomes thicker each year, it is due to lateral meristems.

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