movement across membranes

• passive


  simple and facilitated diffusion and osmosis, with the concentration gradient
• active


  against the concentration gradient, requires ATP
• simple diffusion


  oxygen, carbon-dioxide, and lipid-soluble molecules or uncharged particles
• protein channels


  charged or larger molecules, ions, glucose
• osmosis


  movement of solvents from low concentration to high concentration
• isotonic


  when the concentration levels inside and outside the cell are the same
• hypotonic


  water enters the cell since there is a higher concentration level inside the cell
• hypertonic


  water leaves the cell since there is a lower solute concentration inside the cell
• plasmolysis


  when a plant cell is placed in a hypotonic solution, it becomes flaccid