The basic steps of light-dependent reactions are:
• Light absorption in Photosystem II (PSII) and excitation of PSII
• ATP synthesiS-proton gradient in electron transport chain isdriving ATP production in a process of chemiosmosis
• Light absorption in Photosystem I (PSI) and excitation of PSI
• Reduction of NADP+ and the photolysis of water.
Based on the image, it seems that the picture is of the layers of the atmosphere. Now the B layer is the thermosphere. It is found in between the mesosphere (layer below) and the ionosphere (layer above). It extends up to 600 km high and you can find satellites and the aurora here. Temperature here is higher as the height increases and it is because of this trait, its name thermosphere was based on on. "Thermo," in Greek means heat. It overlaps with the ionosphere.
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