Ions that move across the cell membrane from low concentrations to high concentrations are most likely * diffusing through ion channels. using energy during the process of active transport. moving through a protein. both (a) and (b).

The large increase in atmospheric carbon dioxide in the last 50 years most likely comes from a. an increase in cellular respiration b. increased decomposition by bacteria c. an increase in the burning of fossil fuels d. an increase in photosynthesis