Photosynthesis

It’s sometimes said that trees are built from thin air and water.

This is because the food that fuels a tree’s growth basically comes from carbon dioxide (breathed in through the leaves) and water (absorbed through the roots).

There are other nutrients that the roots extract from the soil, but these are only required in small quantities.

Unlike animals, trees manufacture their own food internally. They also retain their own waste products produced during growth, storing them internally in the heartwood cells.

Trees are extremely efficient solar-powered production plants, since the only external energy source needed to carry out these functions is the sun.

How photosynthesis works

The process used by plants to manufacture food is called photosynthesis, because it uses the power of sunlight (‘photo’ meaning ‘light’) to ‘synthesise’ the carbon dioxide with water.

Air enters through thousands of tiny pores called stomata, which are mostly found on the underside of the leaves. The sunlight is turned into energy by chlorophyll, a green pigment in the leaves. Water and other nutrients are absorbed by the roots and transported to the leaves through the sapwood, or xylem tissue.

The carbon dioxide and water are converted into glucose in the leaves. Glucose is a sugar, sometimes referred to as a simple carbohydrate. The main by-product of this manufacturing process is oxygen, which is released back into the air.

The glucose molecules are carried to all the growing parts of the tree through the phloem, or inner bark. When they reach the areas where they’ll be used, they are converted to more complex carbohydrates, such as cellulose and starch. Cellulose is the basic body-building material of plants, and the main component in wood.

Starch is used for storage purposes when there is excess food being produced. This reserve supply is mostly stored in the ray cells, which extend outwards from the centre of the tree towards the bark.

The basic formula used to describe the process of photosynthesis is: