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Around 2 Ga, an increase in atmospheric oxygen levels took place, causing an oxidation of H 2 S in the surroundings and an increase in the pH of the sea water. The resulting environment had become more oxidizing and thus allowed the later incorporation of the heavier metals such as copper and zinc .
The strong bonding of metals in liquid form demonstrates that the energy of a metallic bond is not highly dependent on the direction of the bond; this lack of bond directionality is a direct consequence of electron delocalization, and is best understood in contrast to the directional bonding of covalent bonds.
Photosystem II obtains electrons by oxidizing water in a process called photolysis. Molecular oxygen is a byproduct of this process, and it is this reaction that supplies the atmosphere with oxygen. The fact that the oxygen from green plants originated from water was first deduced by the Canadian-born American biochemist Martin David Kamen.
The bond between a water molecule and the metal ion is a dative covalent bond, with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by hydrogen bonds to other water molecules. The latter are said to reside in the second coordination sphere.
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants , algae , and cyanobacteria .
Plastocyanin is believed to work less like an enzyme where enzymes decrease the transition energy needed to transfer the electron. Plastocyanin works more on the principles of entatic states where it increases the energy of the reactants, decreasing the amount of energy needed for the redox reaction to occur.
The oxygen-evolving complex (OEC), also known as the water-splitting complex, is a water-oxidizing enzyme involved in the photo-oxidation of water during the light reactions of photosynthesis. [3] OEC is surrounded by 4 core proteins of photosystem II at the membrane-lumen interface.
C 4 photosynthesis reduces photorespiration by concentrating CO 2 around RuBisCO. To enable RuBisCO to work in a cellular environment where there is a lot of carbon dioxide and very little oxygen, C 4 leaves generally contain two partially isolated compartments called mesophyll cells and bundle-sheath cells.