Answer:
D. Population genetics
Population genetics is the study of genetic variation within populations, and involves the examination and modelling of changes in the frequencies of genes and alleles in populations over space and time. ... In natural populations, however, the genetic composition of a population's gene pool may change over time.
Explanation:
microevolution - evolutionary change within a species or small group of organisms, especially over a short period. (Not studying the overall evolution in the population, just a single allele usually) Not it then
macroevolution - Macroevolution in the modern sense is evolution that is guided by selection among interspecific variation, as opposed to selection among intraspecific variation in microevolution (this goes over huge groups of different species) Not it then
gene pool - The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. (Not the study of evolution in a population) Not that then
So it has to be D
It requires energy when a substance must travel against a concentration gradient through the membrane
