Wood consists of xylem cells, and bark is made of phloem and other tissues external to the vascular cambium.
As a tree grows, it may produce growth rings as new wood is laid down around the old wood.
Plants also do some respiration using oxygen the way animals do.
They need oxygen as well as carbon dioxide to live.
This way, wood taken from trees in the past can be dated, because the patterns of ring thickness are very distinctive. Very few tropical trees can be accurately dated in this manner.
The roots of a tree are almost always underground, usually in a ball shaped region centered under the trunk, and extending no deeper than the tree is high.
The parts of a tree are the roots, trunk(s), branches, twigs and leaves.
Tree stems are mainly made of support and transport tissues (xylem and phloem).
Trees absorb carbon dioxide and potentially harmful gasses, such as sulfur dioxide, carbon monoxide, from the air and release oxygen.
One large tree can supply a day's supply of oxygen for four people.