ATP, a higher-energy molecule than ADP, is synthesized from ADP in the electron transport chain. Given that molecules cannot go from a lower energy to a higher energy on their own without an external input of energy, how does the energy for this reaction enter the system?

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before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.

yes

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blue is scattered more than other colors because it travels as shorter, smaller waves. this is why we see a blue sky most of the time.