3.3.2 The Xylem & Phloem

Question 1

Xylem Function

Answer 1

The functions of xylem tissue in a plant are:
- vascular tissue that carries dissolved minerals and water up the plant
- structural support
- food storage

Question 2

Xylem Location

Answer 2

Xylem tissue is found, along with the phloem and other tissues, in vascular bundles
The location of vascular bundles is dependant on which organs are under different stresses:
- in the roots, the vascular bundle is found in the centre and the centre corer of this is xylem tissue - this helps the roots withstand the pulling strains they are subjected to as the plant transports water upwards and grows
- in the stems, the vascular bundles are located around the inside and the xylem tissue is found on the inside (the closest to the centre of the stem) to help support the plant
- in the leaves, vascular bundles form the midrib and veins and therefore spears from the centre of the leaf in a parallel line - the xylem tissue is found on the upper side on the bundles (closet to the epidermis)

Question 3

Phloem Function

Answer 3

The function of phloem tissue in a plant is to:
- transport organic compounds, particularly sucrose, from the source (e.g. a leaf) to the sink (e.g. roots)
- the transport of these compounds can occur up and down the plant

Question 4

Phloem Structure and Location

Answer 4

The phloem is a complex tissue also made up of various cell types
Its bulk is made up of sieve tube elements, which are the main conducting cells, and companion cells
Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres
The location of the vascular bundles is dependent on which organ they are in as the different organs are under different stresses:
- in the roots, the vascular bundle is found in the centre and on the edged of the centre core is the phloem
- in stems, the vascular bundles are located around the outside and the phloem tissue is found on the outside (closets to the epidermis)
- in the leaves, vascular bundles form the midrib and veins and therefore spread from the centre of the leaf in a parallel line - the phloem tissue is found on the lower side of the bundles (closet to the lower epidermis)