Plant+Tissues+and+Tissue+Systems

Plant Tissues and Tissue Systems

Overview of Plant Tissues

  • All plants originate from a single fertilized egg cell.
    • Fertilization Process:
    • Pollen enters the ovary and fertilizes the egg, leading to cellular reproduction.
    • Cell Proliferation:
    • The single fertilized cell reproduces to create additional cells.
    • Cell Differentiation:
    • Cells undergo differentiation, specializing to perform specific functions within the plant, resulting in diverse cell types.

Characterization of Tissues

  • Continuous organized masses of similar cells are referred to as tissues.
    • Function of Tissues:
    • Groups of cells work collaboratively, forming tissue systems.
    • Types of Plant Tissues:
    1. Meristematic Tissues
    2. Vascular Tissues (e.g., Xylem and Phloem)
    3. Ground Tissues
      • Ground Tissue further sub-divided:
        a) Parenchyma Cells
        b) Collenchyma Cells
        c) Sclerenchyma Cells
    4. Dermal Tissue
      • Provides epidermal coverage, protection, gas exchange, and root water absorption.
      • Specialized features may exist to prevent water loss through evaporation.

Meristematic Tissues

Definition and Location

  • Definition:
    • Meristematic tissues are responsible for plant growth.
  • Locations:
    • Found in various plant regions.
  • Types of Meristematic Tissues:
    1. Apical Meristems:
    • Located at the tips of roots and shoots.
    • Responsible for elongation of both roots and shoots, contributing to plant height and root depth.
    1. Lateral Meristems (Vascular Cambium):
    • Found in many plant species including dicots and gymnosperms, but absent in monocots.
    • Responsible for growth in girth.
    1. Intercalary Meristems:
    • Located at the bases of mature leaves in monocots, between regions of mature tissue.
    • Enable rapid regrowth after grazing; evolved as a response to herbivore damage.

Structure and Function

  • Mature plant cells are encased in a rigid cell wall, which limits division in mature cells.
  • New Plant Cells:
    • Newly produced cells are small initially, characterized by thin and flexible primary cell walls made from cellulose and pectin.
    • When growth ceases, cells develop a more rigid secondary cell wall, potentially reinforced with lignin, enhancing structural support.

Apical Meristems

Location and Functionality

  • Apical meristems are found at the tips of roots and shoots.
    • Responsible for the increase in plant length and contributes to vertical growth.
    • Facilitate increased depth in the roots of both dicot and monocot plants.

Lateral Meristems (Vascular Cambium)

Classification of Plants

  • Plants can be categorized into:
    • Flowering Plants (Angiosperms)
    • Gymnosperms (Plants with Cones)
  • Classification of Angiosperms into:
    • Dicots
    • Monocots

Function and Effect

  • Lateral meristems increase the girth of the plant; found just below the bark in woody species.
    • Cell division results in the formation of growth rings characteristic of woody plants.

Dendrochronology

  • Definition:
    • Dendrochronology is the scientific method of dating tree rings (growth rings) to ascertain the exact year they were formed.
    • It provides insights into past climates, ecosystems, and cultures.
    • Applications:
    • Enables dating of wooden structures and understanding historical weather conditions (e.g., thicker rings indicate wet years, thinner rings indicate dry years).
    • Utilizes patterns and sequences for correlation with well-known historical timelines and events.

Intercalary Meristems

Characteristics in Monocots

  • Located near the nodes of monocots (e.g., grasses).
    • Position allows for quick regrowth following damage or grazing.
    • Adaptation for herbivory— allows the plant to survive grazing by herbivores while still permitting growth.

Structure of Plant Stems

  • Grass stems are composed of nodes and internodes:
    • Nodes: Solid and larger parts of the stem.
    • Internodes: Hollow sections between nodes.
    • Intercalary meristems promote leaf growth from the node.

Vascular Tissue

Overview

  • Function of Vascular Tissue:
    • Responsible for the movement of water, food, and nutrients throughout the plant.
  • Two Main Types:
    1. Xylem
    2. Phloem

Xylem

  • Role:
    • Transport of water and nutrients from roots to aerial parts of the plant.
    • Provides structural support via thick cell walls rich in lignin.
  • Major structural features include visible veins in leaves.

Phloem

  • Function: