Complex Permanent Tissues

The plant’s vascular transport network: moving water, minerals, and food across every root, stem, and leaf.

1. What are Complex Permanent Tissues?

Complex permanent tissues consist of multiple specialized cell types working together as a single transport unit. Together, they constitute the vascular system of vascular plants.

2. Xylem Tissue

• Primary Function: Unidirectional transport of water and dissolved mineral ions from roots upward to leaves, alongside heavy mechanical support.

Components of Xylem:

1. Xylem Vessels: Long, continuous, hollow tubes formed by dead cells placed end-to-end with perforated or dissolved end walls. They resist high water tension and serve as the main water-conducting elements in angiosperms.
2. Tracheids: Elongated dead cells with tapering ends and lignified walls containing pits for lateral water movement.
3. Xylem Parenchyma: The only living component of xylem; stores food and assists in short-distance lateral transport.
4. Xylem Fibers: Dead, thick-walled sclerenchymatous fibers providing rigidity and mechanical support.

3. Phloem Tissue

• Primary Function: Bidirectional translocation of synthesized organic food (sucrose/sugars) from leaves to all growing regions and storage organs.

Components of Phloem:

1. Sieve Tube Elements: Long, living, column-like cells connected end-to-end. End walls feature fine pores forming sieve plates. Mature sieve tubes lack a nucleus, ribosomes, and large vacuoles to maximize internal flow space.
2. Companion Cells: Specialized living parenchyma cells attached to sieve tubes via plasmodesmata. They possess a prominent nucleus and dense mitochondria to regulate metabolism and supply metabolic energy (ATP) for translocation.
3. Phloem Parenchyma: Living storage cells assisting in lateral food distribution.
4. Phloem Fibers: Dead sclerenchymatous fibers providing tensile strength (e.g., commercial jute fibers).

Summary Comparison: Xylem vs. Phloem

Characteristic	Xylem Tissue	Phloem Tissue
Transported Substance	Water and dissolved mineral salts	Synthesized organic food (sucrose/sugars)
Direction of Flow	Unidirectional (Upward from roots only)	Bidirectional (Upward and downward)
Nature of Conducting Cells	Dead cells (Vessels & Tracheids)	Living cells (Sieve Tube Elements)
Structural Wall Material	Lignified thick walls	Cellulose thin walls
Associated Regulatory Cell	None	Companion Cells

Grade 11 Science English Medium – Plant Tissues