Plant Transport Systems

Plants have a transport system to move water, minerals, and products of photosynthesis around the organism.
This system is comprised of xylem and phloem, two specialised types of vessel that have evolved to fulfil different roles.

Xylem vessels are responsible for the upwards transport of water and minerals from the roots to the rest of the plant.
They consist of dead cells that have had their ends removed, forming a continuous, hollow tube.
The walls of xylem vessels are strengthened by a substance named lignin, which prevents the vessels from collapsing under pressure.
Water movement is largely driven by transpiration, a process where water evaporates from the leaves creating a column of water in the xylem which is pulled upward.

Phloem vessels, on the other hand, transport food in the form of sugars, a product of photosynthesis, from the leaves to the rest of the plant.
Unlike the xylem, phloem consists of living cells.
These cells have small holes in their end walls, allowing dissolved sugars to move up and down the plant.
The process of sugar transport in plants is known as translocation.

In the plant’s stem, the xylem and phloem form bundles, usually with the phloem on the outside and the xylem on the inside. This gives the stem strength.

In the leaves, xylem and phloem form veins which form a transport and support network.
These veins also help to maintain the shape of the leaf.

Plant roots have tiny hair-like extensions known as root hairs which increase the surface area for water absorption.
Root hairs are close to the xylem vessels, which means that water doesn’t have to travel far to be transported up the plant.
Similarly, leaves have stomata, small pores mainly located on the underside, which allows for the exchange of gases and the escape of water vapour, driving transpiration.