Synovial cavities are exposed to the external environment.

A. Ionic: Ionic bonds involve the complete transfer of electrons from one atom to another, creating oppositely charged ions that attract each other. In water, oxygen and hydrogen share electrons rather than transfer them.

B. Peptide: Peptide bonds form between amino acids during protein synthesis, linking the carboxyl group of one amino acid to the amino group of another. Since water is a simple molecule, not a protein, peptide bonds are not involved in its formation.

C. Polar covalent: Polar covalent bonds occur when atoms share electrons unequally due to differences in electronegativity. In water, oxygen pulls the shared electrons closer to itself, creating a partial negative charge on oxygen and partial positive charges on the hydrogens.

D. Nonpolar covalent: Nonpolar covalent bonds involve equal sharing of electrons between atoms with similar electronegativity. Because oxygen is more electronegative than hydrogen, the sharing in water is unequal.

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.