Enzymes ___ the activation energy threshold required to start a chemical reaction lower or raise

lower

Explanation:

Enzymes are chemical substances or biological molecules that catalyze biological reactions by lowering the activation energy threshold required to start such reactions.

The activation refers to the minimum energy that must be conquered by the reactants in a chemical reaction in order to cross over to the product's side.

Enzymes work by lowering this energy and hence, making the crossing over to the product's side faster than normal. They are not themselves used up in reactions and can always be recovered and reused.

Correct answer: lower

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.