Which statement describes a difference between the nitrogen and carbon cycles? The nitrogen cycle occurs entirely in the ocean.

The nitrogen cycle requires a process called nitrogen fixation that is carried out by certain bacteria.

The carbon cycle requires freezing temperatures.

The carbon cycle involves only plants.

Which of the following factors would not contribute to allopatric speciation? a) a population becomes geographically isolated from the parent population.b) the separated population is small, and genetic drift occurs.c) the isolated population is exposed to different selection pressures than the ancestral population.d) different mutations begin to distinguish the gene pools of the separated populations.e) gene flow between the two populations is extensive.