Photosynthesis and cellular respiration are the same chemical reactions headed in opposite directions. Photosynthesis takes carbon dioxide and water and produces carbohydrates and oxygen. Cellular respiration takes carbohydrates and oxygen and produces carbon dioxide and water. Respiration is the exothermic reaction. Photosynthesis requires the input of energy from the sun in order to proceed. In the economy of ecology, why are both reactions necessary? How did the cycling of solar energy through the biosphere begin? How can it be best maintained today?
–Please help me understand this alittle better.
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Actually it was an Al G bloom
Al Gore did it for fun.
First, to be precise, nobody actually knows for sure. We do not even know exactly when life, as distinct from non-living chemical activity, began. Prior to life on earth, the elemental chemical composition of the earth was constant, same as now, but the molecular chemical composition was different. There was likely no free oxygen, the predominant gaseous materials likely being water vapor, methane, and ammonia. Once the average earth surface temperature dropped below the boiling point of water, life as we know it became possible. It is believed that various solar energy and atmospheric effects caused complex chemicals to form in puddles at the boundary between land and sea, and that, over time, these puddles became the first primitive living cells. Initial metabolism would have to have been based on methane, ammonia, water, and carbonates from rocks. Eventually, early bacteria-like creatures changed the atmosphere into something more similar to the present one, and this enabled the development of sugar formation (CO2 plus H2O plus energy) with oxygen as a byproduct, and the metabolism of sugar (CH2OHx plus O2 yields energy) with oxygen to obtain energy and get back the CO2 and H2O. There is evidence that this process was well under way 2 billion years ago.
To be clear, neither photosynthesis nor cellular respiration are necessary in any cosmic sense – they are features of certain life forms that developed somehow on earth and exist to this day. Without these reactions, those life forms would not exist, but perhaps others could and would. In any case, the biosphere exists because there is solar energy, which has been irradiating the earth since the formation of the solar system. Life has developed the ability to trap solar energy and use it for plant growth, which in turn supports animal life, which closes the mass and energy loop by providing equal and opposite chemical activity. Every output from every living thing is available as input for other living things, and over time, life develops to exploit all thermodynamic opportunities, no matter how slim or rare. There is no scientific answer to "why"; these are just observed phenomena, which exist, period, whether we understand them or not, whether we can explain them or not, whether they help us out or not.
Now the big question -"how can the balance of oxidation-reduction best be maintained today?" The answer is for man not to engage in oxidation at a greater rate than he can engage in reduction. The burning of fossil fuel at the greatest possible rate has doubled the atmospheric CO2 percentage (from 0.04 to 0.08) in a century and a half, doubling infrared absorption by CO2, raising average surface temperatures a degree or two so far. Those fossil fuels were produced as life forms when the earth was much hotter due to much higher CO2 levels, and also sea level was higher. Fossilization fixed huge amounts of carbon that would otherwise have participated in the greenhouse effect – the earth has been cooler since, on average, than it otherwise would have been, with the resulting accumulation of land ice and the accompanying lowering of average sea level. However, if the greenhouse effects were eliminated completely, the earth would be too far from the sun to have any liquid water at all. It is the presence of CO2 and methane in the atmosphere, trapping the re-radiation of thermal energy derived from absorption of solar visible energy, that heats the surface of the earth enough for water to exist as a liquid and for life as we know it to be possible this far from the sun.
The bottom line is that all natural systems include reciprocal effects, whereas many man made systems do not, resulting in the buildup of some by product (pollution, garbage, CO2, etc.) All human systems must be arranged to recycle, period. Processes that cannot affordably be matched to a reverse process have to be eliminated – the burning of coal and oil for heat energy have to be eliminated because it is thermodynamically impossible to economically reverse combustion – burning is just too exothermic.
There are several "inexhaustible" sources of energy to be tapped – solar radiation, geothermal heat, nuclear fission, tidal flows, and the secondary effects of uneven solar radiation (wind and falling water.) There are technologies for all of these that are feasible now, and which would be cheap enough to compete with coal given sufficient economies of scale and sufficient "fossil fuel combustion taxes" to discourage coal burning. Note that "clean coal" from a global warming perspective cannot exist, given the exothermia of combustion and the impossibility of fixing the CO2 produced by burning at an equal opposite rate.
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