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Permanent Tissue - Complex Permanent Tissues

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notes

Complex Permanent Tissues:

Complex Permanent Tissues comprise of different kinds of cells. These different types of cells coordinate with each other and perform a common function in these tissues. Two Complex Permanent Tissues are- Xylem and Phloem.

(a) Xylem:

This is the tissue that transports water and nutrients from root to upper parts of plant. It is composed of four types of cells i.e., tracheid, vessel, xylem parenchyma and xylem sclerenchyma (fibre).

1.Trachieds are long elongated cells with tapered ending. Trachied cells are dead. Trachied transports water through pits.

2. Vessel is a pipe like structure. Vessels are dead and have lignified thick cell wall. Upper and lower portion of cell wall is absent.

3. Parenchymas are living cells. They store food and nutrients.

4. Sclerenchymas (fibres) are dead cells. They provide mechanical support to plant.

(b) Phloem:

  • Phloem is the tissue that transports food from site of photosynthesis to different parts of plants.
  • It is composed of four types of cell i.e. sieve cells, companion cells, phloem parenchyma, phloem fibre or blast fibre.
  • All types of cells are live except phoem fibres.
  1. Sieve cells are elongated and have thin cell wall. They have cytoplasm but no nucleus and other organelles. These cells are responsible for transportation of food and nutrients
  2. Companion cells have cytoplasm, nucleus and other organelles. They perform the tasks required for sieve cells for living.
  3. Phloem parenchyma store food.
  4. Phloem fibres have thick cell wall and they provide mechanical support to plant.

 

Xylem

Phloem

Made of

Dead Cells

Living Cells

Cell wall thickness

Thick

Thin

Cell wall material

Lignin (rigid)

Celluloses

Permeability

Impermeable

Permeable

Cytoplasm

None

Cytoplasm lining

Transports…

Water & minerals

Food

Carried to….

Leaves

Growing parts & storage organs

Direction of flow

Upwards

Up & down

Tissue also has

Fibres

Companion cells

notes

Complex Permanent Tissues:

Tissues made of more than one type of cell coordinating to perform a common function.

1) Xylem:

It helps in the conduction of water and minerals from roots to the upper parts of the plant.

It consists of -

  • Tracheids

  • Vessels

  • Xylem parenchyma

  • Xylem fibers

2) Phloem:

It transports food material prepared in leaf/ green parts to other parts of the plants.

It consists of –

  • Sieve tubes

  • Companion cell

  • Phloem parenchyma

  • Phloem fibers

Example

What are the constituents of phloem?

Phloem is a living tissue in vascular plants which conducts the soluble organic compounds synthesized during photosynthesis downwards from the leaves.

Listed below are the constituents of phloem:

  • Companion cells: it appears to check the activity of the adjacent sieve element and participates in loading and unloading of the sugar into the sieve element 
  • Sieve tubes: these elongated living cells, conveys carbohydrates, chiefly sucrose from leaves to roots and fruits
  • Phloem fibres: they are commercially useful as they possess great pliability and tensile strength 
  • Phloem parenchyma: also known as transfer cells, they are found near the finest branches, ends of sieve tubes in leaf veinlets, functional here in conveying food.
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