Date produced: Original versions in May 2006, then updated March 2008.
Carbon Dioxide, water, nutrients from soil and light are used by the tree in its photosynthesis processes (within its leaves) to produce energy-rich compounds that are used by the tree. A by-product of this same process is oxygen (Attenborough, D., Life on Earth, William Collins and BBC, Glasgow, 1979). Enormous numbers of ancient plants over an extremely long time changed the Earths atmosphere from having very little oxygen, to having a reasonably large proportion of oxygen within it (Attenborough, D., Life on Earth, William Collins and BBC, Glasgow, 1979). Animals now require oxygen for their life processes. Without having enormous amounts of photosynthesis within the biosphere to maintain close to current levels of oxygen in the atmosphere, the effect on all animal life (including us, of course) would be catastrophic.
This computer painting tries to show a new (pale blue) gas exiting the tree after the tree consumes a yellowy brown gas (carbon dioxide) in the presence of sunlight. The other most important ingredient however is water, which provides the actual oxygen (as a by-product of having the hydrogen used in the photosynthesis processes). Ive tried to indicate the water in the final version.
The photosynthesis processes involved are then represented in the strips below the pictorial image. The second strip represents the way that animals return carbon dioxide from taking in oxygen.