Plant organisation

The main roles of plant stems and roots are to transport substances around the plant. They have two types of transport systems – xylem and phloem. Xylem transports water and minerals. Phloem transports sugars and amino acids dissolved in water.

These are distributed differently in roots and stems. In the root, the xylem forms a central column. It forms a solid support. The phloem is towards the centre, outside the xylem.

In the stem, the transport tissues of the xylem and phloem are grouped into vascular bundles.

Cross section of a plant root and plant stem

Any green part of a plant above ground, where it is exposed to light, can photosynthesise. But a plant’s leaves are the main organ of photosynthesis.

Plant leaves are adapted for gas exchange and photosynthesis.

Diagram of a plant leaf
Large surface areaFor maximum absorption of light. For optimum absorption of carbon dioxide.
A thin, flattened blade - though there are exceptionsSo that water and gases have a limited distance to diffuse.
Vascular tissue in the midrib and veinsBranches of the xylem, to transport water and minerals to the leaf. Branches of the phloem. To transport glucose and other products of photosynthesis to other parts of the plant.
Air spaces between cells within the leafFor the diffusion of gases.