s mentioned above, few marine organisms have been shown to rely solely on passive carbon dioxide uptake, but the carbon dioxide concentrating mechanisms are often unknown. As stated in a review article in 2005, marine diatoms fix more than 10 billion tons of carbon by photosynthesis each year, but "there are still a number of fundamental unresolved aspects of inorganic carbon assimilation by marine diatoms. It is not clear how the carbon-concentrating mechanism functions."
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.
What are diatoms?:: Diatoms of the United States
About the time that the continents began to grow and began, Earth produced its first known glaciers, between 3.0 and 2.9 bya, although the full extent is unknown. It might have been an ice age or merely some mountain glaciation. The , and numerous competing hypotheses try to explain what produced them. Because the evidence is relatively thin, there is also controversy about the extent of Earth's ice ages. About 2.5 bya, the Sun was probably a little smaller and only about as bright as it is today, and Earth would have been a block of ice if not for the atmosphere’s carbon dioxide and methane that absorbed electromagnetic radiation, particularly in the . But life may well have been involved, particularly oxygenic photosynthesis, and it was almost certainly involved in Earth's first great ice age, which may have been a episode, and some pertinent dynamics follow.
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Diatoms are extremely unique organisms. They are extremely abundant photosynthetic algae, with a few exceptions which are heterotrophic or mixatrophic. They store energy in the form of oils and they usually produce extra cellular polysaccharides. But on top of it all they have cell walls. Their cell walls aren’t made of cellulose or peptidoglycan or any other complex organic molecule. Instead they are surrounded in a silica (glass) cell wall which is often call frustules.