Photosynthesis

Generically, in the biological process of photosynthesis, a large number of organisms (e.g., plants, algae and particular bacteria) capture the energy of photons in sunlight, transforming that radiant energy into biochemical energy-rich molecules, through a series of physico-chemical reactions with the starting materials, water and carbon dioxide, often abundant in their environment &mdash; the photosynthesizing organisms, and the organisms that feed on them, using those energy-rich molecules as substrate and energy source, enabling the cellular functions that maintains nearly every living system on Earth in the living state.

Inasmuch as the etymological definition of photosynthesis, "synthesis with light", can apply to other light generating phenomena outside biology, a leading researcher in photosynthesis, Robert E. Blankenship, in the Department of Chemistry and Biochemistry at Arizona State University, suggests this succinct core definition of photosynthesis:

This article will classify the differing types of photosynthesizing organisms, and describe the details of the differing photosynthetic mechanisms employed by them. It will also discuss the implications of photosynthesis in the sciences of biology, geology, oceanography, climatology, and other areas of importance to the life of planet Earth, since without photosynthesis nearly every species on Earth would perish.

Preliminarily, the reader might refer to the following:    Morton O. (2008) Eating the Sun: How Plants Power the Planet. HarperColins. ISBN 0007163649, ISBN 978-0007163649 (hbks).


 *  Publisher´s description:  A story of a world in crisis and the importance of plants, the history of the earth, and the feuds and fantasies of warring scientists—this is not your fourth-grade science class's take on photosynthesis….From acclaimed science journalist Oliver Morton comes this fascinating, lively, profound look at photosynthesis, nature's greatest miracle. Wherever there is greenery, photosynthesis isworking to make oxygen, release energy, and create living matter from the raw material of sunlight, water, and carbon dioxide. Without photosynthesis, there would be an empty world, an empty sky, and a sun that does nothing more than warm the rocks and reflect off the sea. With photosynthesis, we have a living world with three billion years of sunlight-fed history to relish….Eating the Sun is a bottom-up account of our planet, a celebration of how the smallest things, enzymes and pigments, influence the largest things¬¬—the oceans, the rainforests, and the fossil fuel economy. From the physics, chemistry, and cellular biology that make photosynthesis possible, to the quirky and competitive scientists who first discovered the beautifully honed mechanisms of photosynthesis, to the modern energy crisis we face today, Oliver Morton offers a complete biography of the earth through the lens of this mundane and most important of processes….More than this, Eating the Sun is a call to arms. Only by understanding photosynthesis and the flows of energy it causes can we hope to understand the depth and subtlety of the current crisis in the planet's climate. What's more, nature's greatest energy technology may yet inspire the breakthroughs we need to flourish without such climatic chaos in the century to come….Entertaining, thought-provoking, and deeply illuminating, Eating the Sun reveals that photosynthesis is not only the key to humanity's history; it is also vital to confronting and understanding contemporary realities like climate change and the global food shortage. This book will give you a new and perhaps troubling way of seeing the world, but it also explains how we can change our situation—for the better or the worse.

Overview
Nearly all living systems on Earth depend directly or indirectly on photosynthesis (see below), and for us humans it indirectly provides essentially all of our food-energy, as well the bulk of our non-food energy resources, inasmuch as ancient photosynthesizing organisms produced the energy-rich carbon-containing molecules we combust as fossil fuels &mdash; oil, natural gas &mdash; to generate electricity and other forms of energy we use to support human activity.

In the biological process of photosynthesis in green plants, the leaves capture energy from photons in sunlight, using it to energize electrons, the captured and transformed energy the essential primary energy source driving a set of biochemical reactions that converts carbon dioxide (CO2) and water (H2O) to a carbohydrate compound, a triose, a 3-carbon sugar, and a largely 'waste' product, oxygen (O2) &mdash; thus defining 'oxygenic' photosynthesis. . Triose, as triose phosphates, exit the leaf cell's organelles that synthesizes them &mdash; viz., a chloroplast, condense themselves into six-carbon hexose phosphates, ultimately forming [Dimer|dimers]] like sucrose, or polymers like starch or cellulose, the so-called reduced forms of carbon, reduced in the sense of enrichment in the electrons energized by the captured photons, thus forming of energy-rich carbon compounds that, as mentioned, the photosynthesizing organisms and their predators need to perform the cellular work that maintains them in the living state.

The photosynthetic process effectively stores energy in a variety of energy-rich molecules the photosynthetic organism can metabolize to generate adenosine triphosphate (ATP), the universal circulating and recyclable energy currency of cells, so-called because it can provide the energy needed to drive many of the biochemical reactions necessary to synthesize the macromolecules and molecular intermediates required to maintain the cell in a living state. The process also produces other recyclable forms of circulating energy currency (e.g., NADPH). Photosynthesizing cells thus convert light energy to the life-sustaining chemical energy that drives life-sustaining cellular processes, to paraphrase the words of Professor Blankenship quoted above.

Organisms that photosynthesize function as autotrophs &mdash; viz., organisms that generate their own source of food-energy &mdash; specifically referred to as photoautotrophs. They draw on minerals and other inorganic compounds from the environment and produce an ultimately photon-energy-derived complement of carbohydrates, proteins and lipids that self-organize the photoautotophic organism. In doing so they directly, though blindly, offer themselves as a source of food-energy (e.g., as vegetables, fruits) for consumption by us humans and other organisms, so-called heterotrophs &mdash; viz., organisms that feed on other organisms or on their energy-rich structural components &mdash; and indirectly provide a source of food-energy in the form of the non-human heterotrophs that we humans consume (e.g., chicken, fish and other animals). Photosynthesizing cells also supply the sufficient amounts of oxygen they and we need to generate ATP and NADPH, and they consume the 'waste' CO2 produced in the process of generating ATP.

Not all photosynthesizing organisms produce oxygen. The specific physico-chemical reactions of those that do biologists refer to as oxygenic photosynthesis, and those that do not as 'anoxygenic' photosynthesis. Oxygenic photosynthesis accounts for most of the oxygen in the atmosphere.