Why do plants or trees use sunlight?

How does a tree work?

The water cycle

The roots of the tree absorb water and dissolved minerals from the soil. Now the mineral-rich water has to be transported through the entire shoot system of the tree - i.e. via the trunk into the individual branches and leaves.

The leaves take on a special function, as in their entirety they form a huge evaporation surface. Since water constantly evaporates on the leaves, the tree always has to provide for supplies from the roots.

This creates a steady flow of water from the roots into the leaves. The water mainly evaporates through the stomata of the leaves. At some point it falls back on the earth as precipitation and can be absorbed again through the roots of the tree.

The breathing of the tree

Gas exchange between the tree and the atmosphere takes place through the stomata in the leaves. Like all green plants, the tree absorbs carbon dioxide from the atmosphere and uses light energy to convert it into sugar.

The tree needs sugar as an energy supplier for its growth and metabolic processes. The process of making sugar from carbon dioxide is very complex and is known as photosynthesis.

As a waste product of photosynthesis, the tree releases oxygen, which all living things need to breathe. The tree also breathes and uses oxygen for this. Far less than it produces, however.

The root cells must also be supplied with oxygen and release carbon dioxide. This process is part of what is known as soil respiration.

Bacteria help the tree

In addition to carbon dioxide and oxygen, the tree needs nitrogen to live. However, the tree cannot directly absorb the gaseous nitrogen in our atmosphere.

Nitrogen bacteria in the soil convert the gaseous nitrogen into a form that can be used by the tree and create a nitrogen supply. The tree can then supply itself with it through its roots.

In autumn our native deciduous trees lose their leaves and take a break in which there is hardly any growth. The falling leaves are broken down on the ground together with other organic waste by bacteria and fungi and form what is known as the humus layer, which serves as a mineral reservoir.

If it rains, the minerals are washed out of the humus layer. In this way, the soil gradually gets its minerals back, which can then get back into the tree together with water through the roots.