Which process made an increase in chemical energy for cell activities in organisms living on the earth possible?
a change from a primitive atmosphere, which was about 70 percent nitrogen, to
an atmosphere that was 70 percent oxygen
the development of plants that could add more water vapor to the atmosphere,
increasing the earth's water supply
the discovery of ATP and ADP by scientists for use in the metabolic processes of
cells
a change from a reducing atmosphere where there was no free oxygen to an
oxidizing environment where free oxygen was abundant

the index of refraction of the second medium is higher. i just took the test trust me !

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!