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Arsenic is a moderately abundant element in Earth's crust, and although many arsenic compounds are often considered highly toxic to most life, a wide variety of organoarsenic compounds are produced biologically and various organic and inorganic arsenic compounds are metabolized by numerous organisms.
The fact that a reaction is thermodynamically possible does not mean that it will actually occur. A mixture of hydrogen gas and oxygen gas does not spontaneously ignite. It is necessary either to supply an activation energy or to lower the intrinsic activation energy of the system, in order to make most biochemical reactions proceed at a useful ...
The arsenic (As) cycle is the biogeochemical cycle of natural and anthropogenic exchanges of arsenic terms through the atmosphere, lithosphere, pedosphere, hydrosphere, and biosphere. Although arsenic is naturally abundant in the Earth's crust, long-term exposure and high concentrations of arsenic can be detrimental to human health. [1] [2]
The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds. Hydrogen (H) is the most abundant element in the universe. [1] On Earth, common H-containing inorganic molecules include water (H 2 O), hydrogen gas (H 2), hydrogen sulfide (H 2 S), and ammonia ...
This is one of two core processes in photosynthesis, and it occurs with astonishing efficiency (greater than 90%) because, in addition to direct excitation by light at 680 nm, the energy of light first harvested by antenna proteins at other wavelengths in the light-harvesting system is also transferred to these special chlorophyll molecules.
This unstable allotrope, being molecular, is the most volatile, least dense, and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, As 4. It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97 g/cm 3. [23] Black arsenic is similar in structure to black phosphorus. [23]
Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy. A version of water splitting occurs in photosynthesis, but hydrogen is not produced. The reverse of water splitting is the basis of the hydrogen fuel cell. Water splitting using solar radiation has not been commercialized.
The six aforementioned elements are used by organisms in a variety of ways. Hydrogen and oxygen are found in water and organic molecules, both of which are essential to life. Carbon is found in all organic molecules, whereas nitrogen is an important component of nucleic acids and proteins.