You acquire a soil sample and run an enrichment culture on it. You provide the organisms in the culture with all of the ingredients required for growth except for nitrogen. What result do you expect to have at the end of your experiment?
A) Nitrogen-fixing bacteria will significantly outnumber those incapable of fixing nitrogen.
B) Nitrogen-fixing bacteria will not be present in the culture.
C) Nitrogen-fixing bacteria will be present but not as significantly greater number than non-nitrogen-fixing species.
D) Nitrogen-fixing bacteria will be present, but will be significantly outnumbered by non-nitrogen-fixing species.

Nitrogen-fixing bacteria will significantly outnumber those incapable of fixing nitrogen

Explanation:

Nitrogen-fixing bacteria are capable of growing in a medium lacking organic Nitrogen. They convert (fix) atmospheric Nitrogen (Nitrogen is abundant in air) into organic substrates. Hence, they will grow in the enrichment medium described. This is the kind of medium used to isolate nitrogen-fixing bacteria.

Non-nitrogen fixing bacteria require an organic form of Nitrogen for growth. Hence, in a medium with no nitrogen, they will rely on the Nitrogen fixers. This means delayed growth for them.

A culture medium also has limited nutrients, so the slow growers will have little or no nutrients left.

Therefore, the Nitrogen fixers will have competitive advantage and significantly outnumber those incapable fixing nitrogen.

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!