Answer:
12) When a solid dissolves the solid (solute) and the liquid (solvent) form a very close intimate mixture called a solution
16) In other words, plasma membranes are selectively permeable—they allow some substances through but not others. ... The most direct forms of membrane transport are passive. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement.
19) To move substances against a concentration or electrochemical gradient, the cell must utilize energy in the form of ATP during active transport. Primary active transport, which is directly dependent on ATP, moves ions across a membrane and creates a difference in charge across that membrane.