Which sentence best explains how enzymes speed up a chemical reaction?

enzymes are not changed as a result of a chemical reaction.

enzymes add heat to a chemical reaction.

enzymes remove heat from a chemical reaction.

enzymes lower the activation energy of a chemical reaction.

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.