It is thought by some investigators that cholesterol and sphingolipids self-assemble into microdomains within the plasma membrane that are more gelated and highly ordered than surrounding regions that contain primarily phospholipids. it is hypothesized that certain proteins tend to concentrate in these so-called thereby organizing the membrane into functional compartments. a. microphlogistons b. lipid floats c. flotsam platforms d. lipid rafts

d. lipid rafts

Explanation:

It is thought by some investigators that cholesterol and sphingolipids self-assemble into microdomains within the plasma membrane that are more gelated and highly ordered than surrounding regions that contain primarily phospholipids. It is hypothesized that certain proteins tend to concentrate in these so-called lipid rafts, thereby organizing the membrane into functional compartments.

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.