Xylem vs Phloem: How Plants Move Water and Food
Plants have two transport systems, side by side in the same bundles. Xylem carries water and minerals up from the roots. Phloem carries the sugar made in the leaves to wherever the plant needs it. In the X-ray view of the 3D Plant Anatomy simulator you can watch water rise through the stem.
Xylem vs phloem at a glance
| Xylem | Phloem | |
|---|---|---|
| Carries | Water and dissolved minerals | Sugar, mainly sucrose, and other foods |
| Direction | One way: up from the roots | Both ways: from leaves to roots, fruits and growing tips |
| Cells | Dead, hollow tubes | Living sieve tubes with companion cells |
| Walls | Thick and strengthened with lignin | Thin |
| Driven by | Water evaporating from leaves pulls water up | Pressure pushes sugar sap from where it is made to where it is used |
| In a tree trunk | The wood | A thin layer just inside the bark |
| Also does | Holds the plant up | Carries signals and some hormones |
How water climbs
Water evaporates from tiny pores in the leaves, a process called transpiration. As it leaves, it pulls on the column of water behind it in the xylem, all the way down to the roots. Water molecules cling together so strongly that this pull can lift water to the top of trees over 100 m tall.
How food moves
Leaves make sugar by photosynthesis. The sugar is loaded into the phloem, water follows it in, and the pressure pushes the sweet sap towards roots, fruits, seeds and new shoots. In spring, a tree can send stored sugar back up from its roots to new leaves.
Quick facts
- An easy way to remember: xylem water, phloem food.
- Xylem and phloem run together in vascular bundles, the veins you can see in a leaf.
- Tree rings are layers of xylem, one added each year.
- Aphids feed by pushing their mouthparts into the phloem.
- Ringing a tree, cutting a ring through the bark, cuts the phloem and starves the roots.
See it in 3D
Xylem vs phloem questions
What is the difference between xylem and phloem?
Xylem carries water and minerals up from the roots. Phloem carries sugar from the leaves to the rest of the plant, in both directions.
Is xylem alive or dead?
The water-carrying tubes of xylem are dead, hollow cells. Phloem sieve tubes are alive.
Which way does phloem flow?
Both up and down, from where sugar is made or stored to where it is needed.
Is wood xylem?
Yes. Wood is mostly xylem. The phloem is a thin layer just inside the bark.
What moves water up the xylem?
Mainly transpiration: water evaporating from leaves pulls the water column up from the roots.
More face-offs: see all 3D comparisons.
The 3D Plant Anatomy simulator is made by Julian Neagu, a solo founder in London, as part of VisionVix Simulators. It is free to use in the browser on desktop and phone, with no sign-up.