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other than plants that carries out photosynthesis
Above all else, life is an energy acquisition process. All life exploits the potential energy in various atomic and molecular arrangements, or captures energy directly, as in photosynthesis. Early life exploited the . The chemosynthetic ideal is capturing chemicals fresh to new environments that have yet to react with other chemicals. The currently most-accepted hypothesis has life first appearing on Earth about 3.5-3.8 bya, probably in volcanic vents on the ocean floor. The earliest life forms took advantage of fresh chemicals introduced to the oceans. Life had to be opportunistic and quick in order to capture that energy before other molecules did.
These morphological phenotypes are the bases of most taxonomic classification of an organism, i.e., the organization of the evolutionary relationship among all life on Earth thought to originate from a single ancestral cell type.
Organisms that carry-out photosynthesis are like oxygen factories
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.
Perhaps a few hundred million years after the first mitochondrion appeared, as the oceanic oxygen content, at least on the surface, increased as a result of oxygenic photosynthesis, those complex cells learned to use oxygen instead of hydrogen. It is difficult to overstate the importance of learning to use oxygen in respiration, called . Before the appearance of aerobic respiration, life generated energy via and . Because oxygen , aerobic respiration generates, on average, about per cycle as fermentation and anaerobic respiration do (although some types of anaerobic respiration can get ). The suite of complex life on Earth today would not have been possible without the energy provided by oxygenic respiration. At minimum, nothing could have flown, and any animal life that might have evolved would have never left the oceans because the atmosphere would not have been breathable. With the advent of aerobic respiration, became possible, as it is several times as efficient as anaerobic respiration and fermentation (about 40% as compared to less than 10%). Today’s food chains of several levels would be constrained to about two in the absence of oxygen. Some scientists have and oxygen and respiration in eukaryote evolution. is controversial.
What category of organism carries out photosynthesis?
Somatic cells are produced by simple cell division called mitosis. Somatic cells of multicellular organisms like you are differentiated into special cell types. Skin cells and muscle cells are both somatic cells, for instance, but if you were to examine your skin cells under a microscope and compare them with your muscle cells, you’d see their structures are very different. The various cells that make up your body all have the same basic components (membrane, organelles, and so on), but the arrangements of the elements change from one cell type to the next so that they can carry out various jobs such as digestion (intestinal cells), energy storage (fat cells), or oxygen transport to your tissues (blood cells).
Sex cells are specialized cells that are used for reproduction. Only eukaryotic organisms engage in sexual reproduction. Sexual reproduction combines genetic material from two organisms and requires special preparation in the form of a reduction in the amount of genetic material allocated to sex cells — a process called meiosi. In humans, the two types of sex cells are eggs and sperm.
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Energy and the Human Journey: Where We Have …
When sea levels rise as dramatically as they did in the Cretaceous, coral reefs will be buried under rising waters and the ideal position, for both photosynthesis and oxygenation, is lost, and reefs can die, like burying a tree’s roots. About 125 mya, reefs made by , which thrived on , began to displace reefs made by stony corals. They may have prevailed because they could tolerate hot and saline waters better than stony corals could. About 116 mya, an , probably caused by volcanism, which temporarily halted rudist domination. But rudists flourished until the late Cretaceous, when they went extinct, perhaps due to changing climate, although there is also evidence that the rudists . Carbon dioxide levels steadily fell from the early Cretaceous until today, temperatures fell during the Cretaceous, and hot-climate organisms gradually became extinct during the Cretaceous. Around 93 mya, , perhaps caused by underwater volcanism, which again seems to have largely been confined to marine biomes. It was much more devastating than the previous one, and rudists were hit hard, although it was a more regional event. That event seems to have , and a family of . On land, , some of which seem to have , also went extinct. There had been a decline in sauropod and ornithischian diversity before that 93 mya extinction, but it subsequently rebounded. In the oceans, biomes beyond 60 degrees latitude were barely impacted, while those closer to the equator were devastated, which suggests that oceanic cooling was related. shows rising oxygen and declining carbon dioxide in the late Cretaceous, which reflected a general cooling trend that began in the mid-Cretaceous. Among the numerous hypotheses posited, late Cretaceous climate changes have been invoked for slowly driving dinosaurs to extinction, in the “they went out with a whimper, not a bang” scenario. However, it seems that dinosaurs did go out with a bang. A big one. Ammonoids seem to have been brought to the brink with nearly marine mass extinctions during their tenure on Earth, and it was no different with that late-Cretaceous extinction. Ammonoids recovered once again, and their lived in the late Cretaceous, but the end-Cretaceous extinction marked their final appearance as they went the way of and other iconic animals.
Glossary of scientific terms - What is Life HOME
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, .
The Deep Sea ~ Ocean biology, Marine life, Sea …
Trees first appeared during a plant diversity crisis, and the arrival of seed plants and ferns ended the dominance of the first trees, so the plant crises may have been more about evolutionary experiments than environmental conditions, although a carbon dioxide crash and ice age conditions would have impacted photosynthesizers. The that gave rise to trees and seed plants largely went extinct at the Devonian’s end. But what might have been the most dramatic extinction, as far as humans are concerned, was the impact on land vertebrates. During the about 20% of all families, 50% of all genera, and 70% of all species disappeared forever.
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