Phloem

What is phloem?

Phloem is the vascular tissue in plants that conducts sugars and other metabolic products downward from the leaves.

Phloem Structure

Phloem is composed of:

• Sieve tube elements: arranged end to end to form long tubes.
• Companion cells: provide metabolic support for sieve tube elements.
• Phloem parenchyma: for storage and loading/unloading of sugars.
• Fibers: for support.

Function of Phloem

The primary function of phloem is translocation, which is the transport of sugars (mainly sucrose) produced during photosynthesis to other parts of the plant for growth, storage, and metabolism.

Mechanism of Translocation

Sugars are moved through the phloem via pressure flow:

1. Loading of sugars into sieve tubes at the source (e.g., leaves).
2. Water follows by osmosis, increasing pressure in the sieve tube.
3. The pressure drives the sap (sugar-rich solution) towards the sink (e.g., roots, fruits), where sugars are unloaded.