Transport tissues

In flowering plants, there are two types of tissue used for transporting substances, phloem and xylem. They form separate tubes that go to different parts of the plant, but both types of tissue are completely separate.

Xylem and Phloem Plant Diagram
Xylem and Phloem Plant Diagram

What is Phloem?

The phloem moves food substances that the plant has produced by photosynthesis to where they are needed for processes.

Phloem tubes consist of columns of elongated living cells with small pores at the ends that allow cell sap to flow through. Sap is a liquid that consists of water and substances being transported.

Phloem tubes transport sugars made in the leaves to other parts of the plant so that they can be used immediately e.g. in growth regions or for storage. Transport occurs both up and down the tree, from the leaves to the roots. This is known as translocation.

What is Xylem?

The xylem transports water and minerals from the roots up the plant stem and into the leaves.

A xylem tube is made of dead cells joined end to end with no end walls between them and a hole in the middle. This tube is reinforced with a substance called lignin.

Water and mineral ions are transported from the root to the stem and leaves of the plant via the xylem tube. The transpiration stream is the movement of water from the roots, through the xylem, and out of the leaves.

About the transpiration stream

A plant loses water through transpiration. Throughout a plant's roots and leaves, water moves through the transpiration stream.

  1. The water inside the leaf evaporates and diffuses out, mainly through the stomata tiny holes located on the lower surface.
  2. As a result, there is a slight shortage of water in the leaf, and more water is drawn from the rest of the plant through the xylem vessels to replace it.
  3. The result is that more water is drawn up from the roots, resulting in a constant flow of water through the plant.

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