Which of these statements is true about adaptive evolution?

adaptive evolution is a permanent change in a trait.
adaptive evolution is a temporary change in a trait.
adaptive evolution is a fluctuating change in a trait.

The correct answer is- Adaptive evolution is a permanent change in a trait.

Adaptive evolution can be described as increase in the frequency of alleles that are beneficial to the survival of an organism whereas decrease in the allele frequency that do not give any importance to the survival and reproduction of organism. It results because of natural selection.

Therefore, it depicts a permanent change in a trait as natural selection acts on the heritable traits of an individual.

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.