Trees make food for their growth by photosynthesis. Leaves absorb carbon and oxygen in the form of carbon dioxide. Inside the chloroplast in the cells, the chlorophyll molecules (the plant’s green pigment) use energy from the sun to make the hydrogen from water combine with the carbon and oxygen to form soluble carbohydrate – sugars. The sugars can then be made into starch for storage. Much of this starch is converted into cellulose – the building material for the cells which make up the wood.
Cellulose molecules are made up of long chains of carbon and hydrogen atoms and this is why wood is full of carbon. For as long as that wood is intact, whether as growing trees, timber in buildings and furniture, fibres in paper and books, etc., then that carbon remains locked away in the structure of the wood. Trees need energy to grow. This energy is released from the food made by photosynthesis in a process of respiration
Some of the food is combined with oxygen and the reaction releases stored energy for growth. Respiration uses between a quarter and a half of the food produced in photosynthesis. Respiration uses oxygen and releases energy, carbon dioxide and water. This is the reverse of the photosynthesis which collects the sun’s energy, combines it with carbon dioxide and water and releases oxygen. The combined effect of photosynthesis and respiration is that trees absorb more carbon dioxide from the atmosphere than they release. Trees store or 'lock up' carbon by their natural processes Thus, carbon is effectively ‘locked up’ or ‘sequestered’ by growing trees and will only return to the atmosphere when the tree dies, decays or is cut down and burnt. Products made from wood retain much of the ‘locked up’ carbon within heir structure. It is calculated that the forests of the world hold a carbon stock of over 1,200 billion tonnes, almost double the amount of carbon present as carbon dioxide in the atmosphere.
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