While photosynthesis is highly-evolved in the procaryotes, itapparentlyoriginated in the Bacteria and did not spread or evolve in Archaea.But the Archaea, in keeping with their unique ways, are not withoutrepresentativeswhich can conduct a type of light-driven photophosphorylation. The extremehalophiles, archaea that live in natural environments such as theDeadSea and the Great Salt Lake at very high salt concentration (as high as25 percent NaCl) adapt to the high-salt environment by the developmentof "purple membrane", actually patches of light-harvestingpigmentin the plasma membrane. The pigment is a type of rhodopsin called bacteriorhodopsinwhich reacts with light in a way that forms a proton gradient on themembraneallowing the synthesis of ATP. This is the only example in nature of nonphotosynthetic photophosphorylation. These organisms areheterotrophsthat normally respire by aerobic means. The high concentration of NaClin their environment limits the availability of O2 forrespirationso they are able to supplement their ATP-producing capacity byconvertinglight energy into ATP using bacteriorhodopsin.
The special pigment pair was P870.
The reduction of quinones leades up to take two protons from the cytoplasm.
Chemotrophic growth for the non-sulfur bacteria is achieved by respiration although, there are some exceptional strains obtained by fermentation.
Anaerobic respiration is also linked with this specific growth.
Scientists have discovered that there has been microbial mats deveolping in swine wastewater ditches.
PPNS bacteria were studied by microsopy , biomaker profiling , and PCR cloning.
As with enzymes, the molecules used in biological processes are often huge and complex, but ATP energy drives all processes and that energy came from either potential chemical energy in Earth’s interior or sunlight, but even chemosynthetic organisms rely on sunlight to provide their energy. The Sun thus powers all life on Earth. The cycles that capture energy (photosynthesis or chemosynthesis) or produce it (fermentation or respiration) generally have many steps in them, and some cycles can run backwards, such as the . Below is a diagram of the citric acid (Krebs) cycle. (Source: Wikimedia Commons)
The respiration and photosynthesis cycles in complex organisms have been the focus of a great deal of scientific effort, and cyclic diagrams (, ) can provide helpful portrayals of how cycles work. Photosynthesis has several cycles in it, and Nobel Prizes were awarded to the scientists who helped describe the cycles. Chlorophyll molecules , with magnesium in their porphyrin cages, and long tails. Below is a diagram of a chlorophyll molecule. (Source: Wikimedia Commons)
As with other early life processes, the first photosynthetic process was different from today’s, but the important result – capturing sunlight to power biological processes – was the same. The scientific consensus today is that a respiration cycle was modified, and a in a was used for capturing sunlight. Intermediate stages have been hypothesized, including the cytochrome using a pigment to create a shield to absorb ultraviolet light, or that the pigment was part of an infrared sensor (for locating volcanic vents). But whatever the case was, the conversion of a respiration system into a photosynthetic system is considered to have only happened , and all photosynthesizers descended from that original innovation.
While oxygen level changes of the model show early fluctuations that the model does not, both models agree on a huge rise in oxygen levels in the late Devonian and Carboniferous, in tandem with collapsing carbon dioxide levels. There is also virtually universal agreement that that situation is due to rainforest development. Rainforests dominated the Carboniferous Period. If the Devonian could be considered terrestrial life’s , then the Carboniferous was its . In the Devonian, plants developed vascular systems, photosynthetic foliage, seeds, roots, and bark, and true forests first appeared. Those basics remain unchanged to this day, but in the Carboniferous there was great diversification within those body plans, and Carboniferous plants formed the foundation for the first complex land-based ecosystems. Ever since the episodes, there has , and the that have prominently shaped Earth’s eon of complex life probably always began with ice sheets at the South Pole, and the current ice age arguably is the only partial exception, but today’s cold period really began about 35 mya, .
It can be helpful at this juncture to grasp the cumulative impact of , inventing , inventing , inventing that made possible, and inventing . Pound-for-pound, the complex organisms that began to dominate Earth’s ecosphere during the Cambrian Period consumed energy about 100,000 times as fast as the Sun produced it. Life on Earth is an incredibly energy-intensive phenomenon, powered by sunlight. In the end, only so much sunlight reaches Earth, and it has always been life’s primary limiting variable. Photosynthesis became more efficient, aerobic respiration was an order-of-magnitude leap in energy efficiency, the oxygenation of the atmosphere and oceans allowed animals to colonize land and ocean sediments and even fly, and life’s colonization of land allowed for a . Life could exploit new niches and even help create them, but the key innovations and pioneering were achieved long ago. If humanity attains the , new niches will arise, even of the , but all other creatures living on Earth have constraints, primarily energy constraints, which produce very real limits. Life on Earth has largely been a for several hundred million years, but the Cambrian Explosion was one of those halcyonic times when animal life had its greatest expansion, not built on the bones of a mass extinction so much as blazing new trails.
The Cambrian Explosion’s iconic animal was the . As a child, I read every paleontology text in my elementary school’s library, and I have fond memories of imagining trilobite lives. Was there love among the trilobites? Among the protists? The bacteria? To a scientist, those questions might be unanswerable and even meaningless, but a mystic might pursue them. I will not wax too mystically in this essay (I do it ), but that may well be the big question of life on Earth and . The nature of consciousness and love in the Cambrian, or the lack thereof, as much as it may always be a mystery, does not invalidate life’s arc through the evolutionary process; it only challenges materialism.
There is also evidence that life itself can contribute to mass extinctions. When the eventually , organisms that could not survive or thrive around oxygen (called ) . When anoxic conditions appeared, particularly when existed, the anaerobes could abound once again, and when thrived, usually arising from ocean sediments, they . Since the ocean floor had already become anoxic, the seafloor was already a dead zone, so little harm was done there. The hydrogen sulfide became lethal when it rose in the and killed off surface life and then wafted into the air and near shore. But the greatest harm to life may have been inflicted when hydrogen sulfide eventually , which could have been the final blow to an already stressed ecosphere. That may seem a fanciful scenario, but there is evidence for it. There is fossil evidence of during the Permian extinction, as well as photosynthesizing anaerobic bacteria ( and ), which could have only thrived in sulfide-rich anoxic surface waters. Peter Ward made this key evidence for his , and he has implicated hydrogen sulfide events in most major mass extinctions. An important aspect of Ward’s Medea hypothesis work is that about 1,000 PPM of carbon dioxide in the atmosphere, which might be reached in this century if we keep burning fossil fuels, may artificially induce Canfield Oceans and result in . Those are not wild-eyed doomsday speculations, but logical outcomes of current trends and , proposed by leading scientists. Hundreds of already exist on Earth, which are primarily manmade. Even if those events are “only” 10% likely to happen in the next century, that we are flirting with them at all should make us shudder, for a few reasons, one of which is the awesome damage that it would inflict on the biosphere, including humanity, and another is that it is entirely preventable with the use of technologies .
For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.