in a model consisting of a non-aqueous layer ( representing the protoplasm ) placed between an inner , more acid , aqueous layer ( representing the sap ) and an outer , more alkaline , aqueous solution ( representing the external solution bathing a living cell ) the penetration of potassium creates an outwardly directed potential against which potassium continues to diffuse inward , thereby increasing the outward potential .
C0175996
protoplasm
C0007634
cell