Final answer:
When a cell is at a resting membrane potential of -70 mV and the equilibrium potential for a cation is +120 mV, both chemical and electrical forces drive the cation into the cell. Chemical forces are due to concentration gradients, while electrical forces are created by the charge separation across the cell membrane.
Step-by-step explanation:
The equilibrium potential for a cation is +120 mV, while the resting membrane potential is -70 mV. When a cell is at the resting membrane potential, both chemical and electrical forces act on ions across the cell membrane. Chemical forces refer to the concentration gradients that drive ions from areas of high concentration to low concentration. Since the equilibrium potential for the cation is higher than the resting potential, the chemical force would encourage the cation to flow into the cell, down its concentration gradient.
Additionally, electrical forces occur due to the separation of charge across the membrane, which results in the creation of an electric field. Because the inside of the cell is more negative than the outside, electrical forces would also encourage positively charged cations to enter the cell, towards the negatively charged interior. The cooperation of these forces at the resting potential indicates that both are indeed directed into the cell, making statement D true.