Monkey's (new world) and primates (old world) have distinctly different vision. most monkey's have dichromatic vision, while primates have trichromatic vision. a. what kind of mutation occurred in the primate lineage to allow the primates to have an extra opsin gene.

Duplication of an ancestral opsin gene occurred in the primate lineage (Old World primates) and subsequent mutations in the new copy resulted in two types of opsin, instead of just one.

Opsins are a group of light-sensitive proteins found in photoreceptor cells (cone cells) of the retina and they are the primary photopigments in primate eyes. Opsins are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade.

The difference in colour vision between New and Old World primates results from differing arrangements of the photopigment genes on the X chromosome. In Old World primates the three photopigments are required for trichromatic colour vision and they are encoded by two or more X-chromosome photopigment genes and an autosomal photopigment gene. New World monkeys typically have only one X-chromosome pigment gene.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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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!