Trees are a plant that usually has a woody stem and bark with one or multiple trunks. They typically grow taller than most other plants and have branches towards the top. Trees are an important part of any ecosystem, providing shelter, shade, preventing erosion and upon death, adding vital nutrients to the soil to be used by other plants. Trees are also a vital habitat for many animals that depend on their fruit and leaves as a food source.
The root system of a tree has several different functions. They anchor the tree into the ground so it does not blow over in high winds, they store food and water for later use by the tree, and they absorb water and nutrients from the ground. Large roots generally are for storage and to anchor the tree like in the case of species that have a tap root that penetrates deep into the soil. The fine root hairs are primarily responsible for absorbing water and nutrients. Many species of trees do not grow very many root hairs and instead depend on a mycorrhizal fungus that lives on the roots to help absorb nutrients.
The stem of a tree is called a trunk. The outer layer of the trunk is the bark. Bark protects the tree from the weather and insects and is decay resistant. Immediately under the bark is a thin layer of cells called phloem. Phloem cells are responsible for transporting sugars down the tree from the leaves. Under the phloem layer is the cambium, this is a layer of living tissue that will develop into new phloem cells on the outer layer or xylem, which is the layer right under the cambium. Xylem cells are hollow tubes that use capillary action to move water and nutrients up the tree from the roots. Under the xylem layer are old dead xylem cells call the heart wood that give a tree its structural strength.
The crown of a tree is the branches and leaves. Leaves are the food manufacturing hub of the tree where sugars are produced using photosynthesis. Leaves take in light and carbon dioxide and release oxygen and water. This process of releasing water vapor into the air is what draws moisture up the tree from the roots using the xylem cells in the trunk and branches. The crown of the tree is also where flowering and fruiting occurs.