(8279) Biology | senior 2 first term 2025 | transport in plant part 2 | xylem and phloem | مستر بيشوي

Overview of the Transport System in Plants

  • The transport system in plants consists of different layers and specialized cells.

Structure of the Stem

  • The stem structure has three main layers:

    • Epidermis:

      • The outermost layer made up of a single row of cells.

    • Cortex:

      • Comprised of several layers, including:

        • Collenchyma: Provides structural support.

        • Other layers: Concerned with storage and various functions.

    • Vascular Cylinder:

      • Divided into four main regions, making it easier to understand.

Detailed Breakdown of the Vascular Cylinder

  • When observing a cross-section of a stem, it resembles a circle or a "cheese-like" shape.

  • Each triangular segment in the vascular cylinder is referred to as the Vascular Bundle:

    • Each bundle consists of:

      • Epidermis Layer: Designated as "E" in diagrams.

      • Cortex: Layers surrounding the vascular bundles.

      • Vascular Cylinder: The central area comprising smaller bundles.

        • Vascular Bundle: Contains further divisions into layers.

          • Xylem: Internal (wet area).

          • Phloem: Outer area that transports nutrients.

        • Cambium: The active division zone important for growth.

        • Pith: Located at the innermost part.

  • Between each vascular bundle lies a region known as Medullary Rays, facilitating transport and support.

Functions of the Vascular System

  • Each vascular tissue serves specific roles:

    • Xylem: Transports water and minerals from roots to leaves.

    • Phloem: Distributes the products of photosynthesis (food).

  • The arrangement of these tissues allows efficient transport within the plant.

Specialized Cell Types in Vascular Bundles

  • Xylem Components:

    • Tracheids and Vessels: Responsible for water transportation.

  • Phloem Components:

    • Sieve Tubes and Companion Cells: Essential for nutrient transportation.

Functional Properties of Vascular Tissues

  • The vascular tissues adapt specially to withstand mechanical stress and facilitate efficient transport.

  • Cohesion and Adhesion within water molecules enhance the movement through xylem.

Importance of the Cambium

  • Cambium acts as a growth layer that differentiates into xylem and phloem, allowing for the increase in thickness of the stem, essential for supporting the plant structure as it grows.

Summary

  • The transport system in plants is a complex arrangement of specialized cells organized into layers, serving vital functions to ensure nutrient and water transport, structural integrity, and growth.