State the functions of xylem and phloem in transport of water, mineral salts and food.

Resources | Subject Notes | Biology

8.1 Transport in Plants

This section explores the vital transport systems within plants, focusing on how water, mineral salts, and food are distributed throughout the organism. The two main tissues responsible for this transport are xylem and phloem.

Xylem

Xylem is a complex vascular tissue in plants responsible for the upward transport of water and dissolved mineral salts from the roots to the rest of the plant.

Function of Xylem:

  • Water Transport: Xylem vessels are specialized for conducting water. The process of water movement through xylem is driven by transpiration, cohesion, and adhesion.
  • Mineral Salt Transport: Mineral salts absorbed by the roots are transported upwards along with water in the xylem.
  • Structural Support: Xylem also provides structural support to the plant, contributing to its rigidity.

Structure of Xylem:

Cell Type Description
Tracheids Long, thin cells with tapered ends. Water moves upwards through pits in the cell walls. Found in all vascular plants.
Vessel elements Wider, shorter cells with perforated end walls (perforation plates). Allow for more efficient water flow. Found in angiosperms.
Xylem Parenchyma Living cells that store food reserves and aid in water transport.

Phloem

Phloem is another vascular tissue in plants responsible for the transport of food (sugars) produced during photosynthesis from the leaves to other parts of the plant where it is needed for growth, storage, or metabolism.

Function of Phloem:

  • Food Transport: Phloem transports sugars (mainly sucrose) produced in the leaves through a process called translocation.
  • Direction of Transport: Phloem can transport food in both upward and downward directions, depending on the plant's needs.
  • Source and Sink: Phloem has a "source" (where sugars are produced, like leaves) and a "sink" (where sugars are used or stored, like roots, fruits, or growing points).

Structure of Phloem:

Cell Type Description
Sieve tube elements Living cells with sieve plates at their ends. These plates facilitate the flow of sap between cells.
Companion cells Supporting cells connected to sieve tube elements. They provide metabolic support to the sieve tube elements.
Phloem Parenchyma Living cells involved in storage and support.

Summary Table:

Feature Xylem Phloem
Function Water and mineral transport Food (sugar) transport
Direction of Transport Upward Bidirectional (upward and downward)
Cells Tracheids, Vessel elements, Xylem Parenchyma Sieve tube elements, Companion cells, Phloem Parenchyma
Suggested diagram: A diagram showing xylem and phloem within a plant, labeling their functions and structures.