How can carbon dioxide be considered a pollutant when it is a natural component of air?
a.
carbon dioxide is considered a pollutant even though it is a natural component of air, because it is harmful to all living organisms.
b.
carbon dioxide is considered a pollutant when larger concentrations than normal are present in the air as a result of human activity.
c.
carbon dioxide is considered a pollutant, because it forms harmful chemicals when mixed with other pollutants in the air.
d.
carbon dioxide cannot be considered a pollutant under any circumstances.

18. determine whether each stateme blank space given. ach statement is true (t) or false (f). place your answer in the 8. when a cell is put into an isotonic solution, individual wat put into an isotonic solution, individual water molecules cannot move back and forth across the cell membrane. d. when a cell is put into a hypertonic solution, there is a net movement of water molecules across the cell membrane into the cell. c. when a cell is put into a hypotonic solution, there is a net movement of water molecules across the cell membrane out of the cell. d. the movement of any solvent across a semi-permeable membrane is called osmosis. e. carrier proteins have the ability to change shape and physically move molecules across the cell membrane. f. in facilitated diffusion, the concentration of the molecules to be moved across the cell membrane is higher inside the cell.