17) Transpiration and Translocation

Phloem Tubes: Translocation of Food

• Function: Phloem tubes transport food substances (mainly dissolved sugars) produced in the leaves to other parts of the plant for immediate use or storage.

• Direction of Flow:

  1. Transport occurs in both directions.

  2. This process is called translocation.

• Cell Sap: The liquid inside phloem tubes that contains dissolved sugars and water.

Xylem Tubes: Water Transport

• Structure:

  1. Made of dead cells joined end-to-end with no end walls, creating a continuous tube with a central hole.

  2. Strengthened by lignin for support.

• Function: Xylem tubes carry water and mineral ions from the roots to the stem and leaves.

• Transpiration Stream:

  • The movement of water from the roots, through the xylem, and out of the leaves is known as the transpiration stream.

Transpiration: Water Loss from the Plant

• Definition: Transpiration is the loss of water vapor from a plant, primarily through the leaves.

• Process:

  1. Water evaporates from the leaf surface, creating a slight water shortage in the leaf.

  2. This shortage causes more water to be drawn up from the rest of the plant through the xylem vessels to replace it.

  3. Consequently, more water is pulled up from the roots, establishing a continuous transpiration stream.

• Adaptation for Photosynthesis:

  • Leaves are adapted for photosynthesis, which requires gas exchange through stomata.

  • Due to higher water concentration inside the plant compared to the outside air, water escapes from the leaves through the stomata.