Earthquakes occur when: A. the earth's plates rub against each other
B. magma squeezes through cracks in the crust
C. eroded sediment is carried away
D. heat and pressure build up under the surface

What is the significance of the protein-lined pits? a. protein attracts other proteins needed for atp synthesis within the cell. b. protein-lined pits are able to transport one molecule at a time down the concentration gradient within the cell. c. the polarity of proteins allows other polar molecules to attach and be transported in the cell by transport channels. d. receptors within the pits allow ligands to fuse and be transported into the cell by endocytosis.