- published: 19 Mar 2012
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Photosynthesis ( /foʊtoʊˈsɪnθəsɪs/; from the Greek φώτο- [photo-], "light," and σύνθεσις [synthesis], "putting together", "composition") is a process used by plants and other organisms to capture the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with carbon dioxide (absorbed from air or water) to form glucose and release oxygen. All living cells in turn use fuels derived from glucose and oxidize the hydrogen and carbon to release the sun's energy and reform water and carbon dioxide in the process (cellular respiration).
Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food, the exceptions being chemoautotrophs that live in rocks or around deep sea hydrothermal vents. The rate of energy capture by photosynthesis is immense, approximately 100 terawatts, which is about six times larger than the power consumption of human civilization. As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115 petagrams of carbon into biomass per year.
The Light falls so softly on the village's roofs
Spreads indistinctly over valleys and plains
The last grasps of daylight hand onto the trees
The branches retracting... becoming one with the night
In their secret places the late birds bed down
In steeples and pylons their life carries on
And in TV-lit windows we all find our home
On the great star-lit landscape we see from the air
We need no more fear of the dark than the morning
For light needs a place it can play
Shadows eclipsing the light that remains
As ten million hot suns beat down on they prey
While one half is blinded the other watches in awe
The universe turning on its infinite way
Watch as the night sky revolves into daybreak
Wait for the first rays of light
Think of new lives, think of new days
Here as the sunlight goes under
Hope our new hopes, dream our new dreams
Think of new worlds without number
And all we can do is imagine the morning
On worlds that we reach in our dreams
The sun is still shining where the eagle set down
And on the people 'neath the westerly sky
But keep our eyes skyward with hope in our hearts