The electrons for photosynthesis come from:

The energy comes from electrons produced by oxidation of biological molecules.

Explanation: In photosynthesis, the energy comes from the light of the sun.

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the supermassive black hole is in the middle of the galaxy.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.