Allele frequencies can change across the geographic range of a species according to climate, geological features, or direction in the range. for instance, a certain allele frequency might go up along with the elevation or down as you go south in the species' range. this systematic change in frequency is referred to as
a. genetic drift.
b. q2.
c. directional selection.
d. a cline.
e. heterosis.

Cline

Explanation:

Cline refers to a noticeable and gradual change of some phenotypic traits over a geographical region. The phenotypic traits such as body size, coloration, etc. exhibit continuous variation or gradient over a geographical region.

Clines result from geographical variations within a species. Clines are usually related to the gradient of abiotic factors such as temperature, pressure, light, altitude. Gene flow between the populations present along the gradient of abiotic factors results in continuous variations in allele frequencies.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!