The Online Library of Knowledge


You are here: Life > Plants > Trees


The dragon's blood treeThe dragon's blood tree A tree is a large plant with a woody stem or trunk, covered with a protective layer of bark. There are two main groups of trees: the broadleaves and the conifers. Trees are a valuable resource. They give us fuel, timber, medicines, food, paper, rubber, fruits, oils and even soap. Even more importantly, they take in carbon dioxide and give off oxygen, so maintaining the balance of gases in the atmosphere

An oak treeAn oak tree

How a tree lives

Like most plants, a tree has roots and a shoot. The shoot is made up of a trunk, its stem, and branches bearing leaves, buds, flowers and fruits (or needles and cones). The trunk holds up the tree while the branches and twigs spread out the leaves so that they receive as much sunlight as possible. The leaves themselves grow in a spiral pattern to avoid shading those below. 

Water containing nutrients from the soil—xylem sap—is drawn up from the soil to the leaves through the sapwood. The leaves use the water and sunlight, as well as carbon dioxide in the air to make food by photosynthesis. This food passes from the leaves to all other parts of the tree as sap through the inner bark (phloem). 

At the base of the tree, a network of roots spreads outwards, anchoring it into the ground. Behind the root tips lie the root hairs which soak up water and nutrients from the soil. A large tree may take up several hundreds of litres of water every day.


Inside a tree trunk

Approximately 25% of all living plant species are trees.
