The proteins in the cell membrane
a. remain in fixed postions
b. allow small molecules that can dissolve lipids to pass into the cell
c. transport certain molecules into or out of the cell
d. prevent osmosis from taking place.

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.