The substances that are present before any chemical reaction are called a. dioxides b. oxygen c. products d. reactants

D.(Reactants)

Explanation: chemical reaction are called the reactants, and the new substances that result are called the products.

identify the dna change shown in the diagram and explain how that change can result in the increased genetic diversity often seen among siblings.

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.