Which type of cellular junction allows for communication between adjacent cells?

A. Each enzyme is chemically specific: Enzymes act only on particular substrates due to the unique shape of their active sites. This chemical specificity ensures that metabolic reactions occur in a controlled and precise manner.

B. Some enzymes make up part of the plasma membrane: Enzymes can be embedded in the plasma membrane, where they catalyze reactions such as breaking down extracellular substances or facilitating signal transduction.

C. Some enzymes are protein plus a cofactor: Many enzymes require non-protein helpers, such as metal ions or vitamins, to function effectively. In such cases, the enzyme is described as a holoenzyme, consisting of the protein part (apoenzyme) plus a cofactor.

D. Enzymes work by raising the activation energy: Enzymes actually lower the activation energy needed for reactions, making biochemical processes proceed more efficiently.

A. In their resting state, all body cells exhibit a resting membrane potential: Every living cell maintains an electrical charge difference across its plasma membrane. Even non-excitable cells display a resting membrane potential, though it is most significant in nerve and muscle cells.

B. The resting membrane potential is maintained solely by passive transport processes: Passive diffusion of ions contributes to membrane potential, but active transport is also required. The sodium-potassium pump actively moves sodium out and potassium in, counteracting passive leaks.

C. The resting membrane potential occurs due to active transport of ions across the membrane due to the sodium-potassium pump: The sodium-potassium pump is vital because it maintains the steep gradients of sodium and potassium. Without this active transport, the gradients would dissipate, eliminating the resting potential.

D. The resting membrane potential is determined mainly by the concentration gradients and differential permeability of the plasma membrane to K+ and Na+ ions: Potassium has the greatest influence since the membrane is more permeable to K+ at rest. Sodium also plays a role, but the relative permeability differences primarily shape the resting potential.