Xylem and phloem

Structure and functions in living organisms · The need for transport and transport in plants · note 2 of 2

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Xylem and phloemSpec 2.53, 2.54

In short

Xylem and phloem are the two transport tissues in flowering plants. Xylem carries water and mineral ions from the roots up to the stem and leaves, in dead, hollow tubes strengthened with lignin. Phloem carries sucrose and amino acids up or down the plant to where they are needed, in living sieve tubes with sieve plates.

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

Xylem

The xylem carries water and mineral ions from the roots to the other parts of the plant, such as the stem and leaves. It is made of dead cells joined end to end.

The cells are dead with no cytoplasm, and the end walls between them have broken down. This makes a continuous hollow tube that water can flow through easily.
The walls are strengthened with lignin. This is strong and waterproof, so it stops the tubes collapsing and helps to support the plant.

Phloem

The phloem carries sucrose and amino acids between the leaves and other parts of the plant. Sucrose is made from the glucose produced in photosynthesis. Phloem is made of living cells, and the substances can move up or down the plant, depending on where they are needed.

Sucrose and amino acids travel from the leaves to growing tips, roots, flowers, fruits and storage organs.
The phloem tubes (sieve tubes) are made of living cells joined end to end. Their end walls have small holes (sieve plates), so the solution can flow from one cell to the next.

Xylem and phloem compared
	Xylem	Phloem
Substances carried	Water and mineral ions	Sucrose and amino acids
Direction	Roots to the rest of the plant (upwards)	Between the leaves and other parts, up or down
Cells	Dead, hollow tubes	Living cells
Cell walls	Strengthened with lignin	Sieve plates in end walls

A stem cross-section with a ring of vascular bundles, phloem on the outer side and xylem on the inner side; a xylem vessel of dead cells forming a hollow tube with no end walls and lignin in the walls, with water and mineral ions moving up from the roots; and a phloem sieve tube of living cells with sieve plates, with sucrose and amino acids moving up and down. — **Xylem**: dead, hollow tubes strengthened with lignin. **Phloem**: living sieve tubes with sieve plates.

A plant with blue xylem arrows carrying water and mineral ions up from the roots through the stem to the leaves, and amber phloem arrows carrying sucrose and amino acids from the leaves, where sucrose is made by photosynthesis, up to the growing shoot tip and down to a fruit, the roots and a storage organ. — Xylem carries water and mineral ions up the plant. Phloem carries sucrose and amino acids up or down to where they are needed.

Common mistake:

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

Quick check

Why can a unicellular organism rely on diffusion?
Show answer
It has a large surface area compared with its volume, so diffusion distances are short.
Which tissue carries water and mineral ions from the roots?
Show answer
Xylem.
Which substances does phloem transport?
Show answer
Sucrose and amino acids.

Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026

Frequently asked questions

Why is diffusion insufficient in multicellular organisms?

Diffusion is insufficient in multicellular organisms because they have a small surface area to volume ratio and most cells are deep inside the body. Diffusion over these long distances is too slow to supply every cell with enough oxygen and food, or to remove waste quickly. So they need transport systems, such as blood, or xylem and phloem.

What is the difference between xylem and phloem?

Xylem carries water and mineral ions upwards from the roots, while phloem carries sucrose and amino acids up or down the plant to where they are needed. Xylem is made of dead, hollow cells with walls strengthened by lignin. Phloem is made of living cells joined end to end, with sieve plates in the end walls.

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