Oxygenic photosynthesis uses two systems for capturing photons. The first one (called ) uses . The second one (called because it was discovered before Photosystem II) uses captured photon energy to add an electron to captured carbon dioxide to help transform it into a sugar. That “” is accomplished by the , and an enzyme called Rubisco, , catalyzes that fixation. Below is a diagram of the Calvin cycle. (Source: Wikimedia Commons)
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.
In light of depiction of low Mesozoic oxygen levels, Peter Ward addressed a controversial issue regarding how dinosaurs breathed. Birds have an air sac breathing system with an inflexible septate lung, which is highly superior to the mammalian . At 1600 meters elevation, today’s birds are about twice as efficient at extracting atmospheric oxygen as mammals are. Flying is the most aerobically demanding activity on Earth and a bird’s air-sac breathing system is a primary reason why they can fly, and is an energetic feat far beyond what any mammal can accomplish. The high-performance respiration that birds possess is also why they live far longer than similarly sized mammals, but is . When a mammal breathes, it inhales oxygenated air and exhales carbon dioxide, but it is not a very efficient system, as fresh and depleted air mix in the lungs. The , on the other hand, passes fresh oxygenated air along the lungs with each breath. One might say that birds constantly inhale. can . Since birds evolved from dinosaurs, and indeed dinosaurs, just when this innovation developed is of great interest to paleobiologists. If the early Mesozoic were the low-oxygen times that GEOCARBSULF depicts, then the air sac system would have been a logical adaptation to oxygen-poor air.
Although the overwhelming devastation of the Permian extinction seemed to play no favorites and whatever survived was the luck of the draw, recent research has demonstrated that even with such a catastrophe, certain life forms were more resilient than others, related to biological “buffers” in their life processes. In marine environments, the warming, anoxia, and acidification would have wiped out species vulnerable to them, and corals were and still are particularly susceptible to those changes. Those conditions wiped out the corals in the Permian extinction, and they are the first ecosystems being devastated today, with similar conditions of . Whether it was the ability to move to safer environs or the ability to buffer chemical changes, the more organisms had a better survival rate than others.
After as little as a half-million years of bedraggled survivors adapting to ice age seas, the ice sheets retreated and the oceans rose. The of the time may have also changed, and upwelling, anoxia, and other dramatic chemistry and nutrient changes happened. Those dynamics are suspected to be responsible for the second wave of extinctions. There also seem to have been .Atmospheric oxygen levels may have fallen from around 20% to 15% during the Ordovician, which would have contributed to the mass death. Seafloor anoxia seems to have been particularly lethal to continental-shelf biomes, possibly all the way to shore. It took the ecosystems millions of years to recover from the Ordovician-Silurian mass extinction, but basic ecosystem functioning was not significantly altered in the aftermath, which is why a has been proposed as a more significant extinction event. The were laid down by the . Most oil deposits were formed in the era of dinosaurs and the processes of oil deposit formation were similar; they were related to oceanic currents. When currents came to shore via the bottom and the prevailing winds blew the top waters offshore, it became a and anoxic sediments could form. When the winds blew onshore and left via the bottom, the waters became clear and are known as nutrient deserts. The oscillation between nutrient traps and nutrient deserts can be seen in oil deposit sediments. In the mid-20th century, Soviet scientists revived an old hypothesis that oil was , a variation of which was also championed by , but improving tools and investigation invalidated those hypotheses. No petroleum geologists today seriously consider the abiogenic origin of hydrocarbons. Oil sediment formation events seem related to mantle and crust processes that created high sea levels and anoxic events, and the last great one was in the , which formed more than 10% of the world's oil deposits.
The diagrams used in this chapter are only intended to provide a glimpse of the incredible complexity of structure and chemistry that takes place at the microscopic level in organisms, and people can be forgiven for doubting that it is all a miraculous accident. I doubt it, too, as . Prokaryotes do not have organelles such as mitochondria, chloroplasts, and nuclei, but even the simplest cell is a marvel of complexity. If we could shrink ourselves so that we could stand inside an average bacterium, we would be astounded at its complexity, as molecules move here and there, are brought inside the bacterium’s membrane, used to generate energy and build structures, and waste products are ejected from the organism. Cellular division would be an amazing sight.
*KH is still important with these soft water fish (maybe not as important as with a Rift Lake Cichlid). The reason is to prevent pH spikes (usually down from other methods used for a soft water environment such as peat or even simply from biological waste breakdown). Generally utilize KH buffers (such as SeaChem Alkaline Buffer or even Baking Soda) to maintain a KH of about 50-80 ppm if necessary.
The use of natural acid buffers such as Frog Moss, Peat, Indian Almond Leaves, and/or Driftwood should also be employed to balance the pH and react with the carbonates provided by the KH, which in turn provides CO2 for live plants that are often kept in this type of aquarium.
Generally Almond Leaves, Driftwood, and many forms of Peat are acid buffers, while Frog Moss tends to be a more fast natural acid buffer.
The use of a chemical acid buffer such SeaChem Acid Buffer should be considered at set up and for water changes (or in between if there are issues with pH climbing or if more CO2 is needed (a KH buffer must be used to cause the reaction that produces CO2).
When one electron shell is filled, electrons begin to fill shells farther from the nucleus. For the simplest atoms it works that way, but for larger atoms, particularly those of metallic elements, electrons fill shells in more complex fashion and electrons begin to fill subshells not necessarily in the shell closest to the nucleus. When an electron is unpaired or in an unfilled shell, it can be a electron, which can form bonds with other atoms. In most circumstances, only unpaired electrons form bonds with other atoms. Electron bonds between atoms provide the basis for chemistry and life on Earth.
However it is not correct to state that just because one does not take extra measures, others should not as well.
It is noteworthy that even experienced aquarists may not be maintaining the best environment possible, as statements such as: prove absolutely nothing!
Good science states otherwise to such statements, the reason being that many fish adapt to poor environments but do not thrive as well as they could.
Also as noted earlier in this article (the KH section); there are NO EXACT ratios as each aquarium is very unique; so testing is 100% required and even then testing should be performed hours or even a day later after addition of mineral and/or buffering products to allow the chemistry to "settle".
With the use of peat, pillow moss, Indian almond leaves (such as Atison's Betta Spa), driftwood and similar; this "settling in" may take weeks.
When two atoms come close to each other, if the potential energy of their combined state is less than their potential energy when they are separate, the atoms will tend to react. But the reaction only happens when the electron shells come into an alignment so that the reaction happen. It is an issue of alignment and the atoms’ velocity. If the shells do not meet in the proper alignment and velocity, the reaction will not happen and the atoms will bounce away from each other. The faster and more often the atoms collide, the likelier they are to react and reach that lower energy state. Chemical (electron shell) reactions need to reach their to occur, and this is measured in temperature. The activation energy for hydrogen and oxygen to react and form water is about 560 degrees Celsius (560o C). Nuclear reactions work in similar fashion, but for nuclear fusion in the Sun’s core, at 16 million degrees Celsius, at a pressure 340 billion times greater than Earth’s atmosphere at sea level, in 10 billion years at one trillion collisions per second, a proton has a 50% chance of fusing with another proton. Nuclear fusion is thus far rarer than electron bonding, and far less energy is released when atoms bond via electrons. The fusion of a helium nucleus releases that it takes to ionize a hydrogen atom. As , some reactions have a cumulative result of , while others . The first can be seen as an investment of energy, while the second can be seen as consuming it. Organisms and civilizations have always faced the investment/consumption decision.
, when a buffer is added to an aquarium with a KH below 50-100, while at the same time there are little acid buffers (either natural or chemical), the pH may bounce.
DO NOT Chase the pH, simply add some form of acid buffer (many are described later too) and/or accept your new pH.
A tank with stable pH of 7.3 and KH of 50-80 for a Betta than one with a KH of under 50 and pH of 6.8!!