Xylem and phloem

Plant structures and their functions · Transport in plants · note 2 of 4

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Xylem and phloemSpec 6.8

In short

Xylem and phloem are the two transport tissues in a plant. Xylem carries water and mineral ions from the roots and is made of lignified dead cells that form hollow tubes. Phloem carries sucrose and is made of living sieve tube cells and companion cells, whose mitochondria release the energy needed for transport.

Xylem and phloem are the two transport tissues in a plant. They run together through the roots, stem and leaves.

Xylem

The xylem carries water and mineral ions from the roots to the rest of the plant. It is made of lignified dead cells.

The cells are dead, with no cytoplasm or nucleus, and the end walls between them have broken down, so they form a continuous hollow tube. Water can flow through easily.
The walls are strengthened with lignin, which is strong and waterproof. This stops the tubes from collapsing and supports the plant.

Phloem

The phloem carries sucrose around the plant. It is made of living cells that use energy to transport sucrose.

Sieve tube cells are joined end to end. The end walls have holes (sieve plates), so dissolved sucrose can pass from cell to cell.
Companion cells are next to the sieve tube cells. They have many mitochondria to release the energy that is needed for the transport of sucrose.

Xylem and phloem compared
	Xylem	Phloem
Substances carried	Water and mineral ions	Sucrose (dissolved in water)
Cells	Dead	Living
Cell walls	Thickened with lignin	Cellulose, with holes in the end walls (sieve plates)
Energy needed for transport	No	Yes

A stem cross-section with a ring of vascular bundles (phloem on the outside, xylem on the inside), next to longitudinal sections of a xylem vessel (hollow tube, lignin rings, water and mineral ions moving up) and phloem (sieve tube cells, sieve plates, companion cells with mitochondria, sucrose moving up and down). — Xylem: dead, hollow, lignified tubes carrying water up. Phloem: living sieve tube cells and companion cells carrying sucrose both ways.

Common mistake:

Do not mix the two up. Xylem = water and mineral ions, dead cells. Phloem = sucrose, living cells.

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

How are root hair cells adapted to their function?

Root hair cells are adapted to absorb water and mineral ions from the soil. The long, thin root hair gives a large surface area, and the thin cell wall gives a short distance to cross. Many mitochondria release energy for the active transport of mineral ions, and concentrated cell sap lets water enter by osmosis.

Why is active transport needed in plant roots?

Active transport is needed because mineral ions, such as nitrate ions, are usually at a lower concentration in the soil water than inside the root hair cell. They cannot move in by diffusion, so they are moved from a lower to a higher concentration by active transport, which uses energy released by respiration in the mitochondria.

How does water move from roots to leaves?

Water moves from roots to leaves in the transpiration stream. Water is absorbed from the soil by root hair cells and moves up through the xylem to the leaves. It evaporates from the cells inside the leaf into the air spaces and diffuses out through the stomata. This loss of water pulls more water up the xylem.

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