1. Chapter 4

2. Transport Across the Cell Membrane  Substances need to move into and out of the cell in order to maintain homeostasis  They can do this by passive or active transport Passive Transport- does NOT require energy Active Transport- does require energy

3. Passive Transport  Does NOT require energy  Substances move from HIGH concentration to LOW concentration Down the concentration gradient

4. Types of Passive Transport  Diffusion  Osmosis  Protein Channels  Facilitated Diffusion

5. Diffusion  Simplest type of passive transport  Does NOT require energy  Random motion of particles from a high concentration to a low concentration  Diffuse down the concentration gradient  Will diffuse until concentration is equal; state of equilibrium

7. Osmosis  Diffusion of water through selective permeable membrane  Does NOT require energy  Water diffuses down the concentration gradient

8. Osmosis  Solution Substance dissolved in another substance  In a solution, some water molecules will be attracted to other molecules and others will not Those that are not attracted are called “free” water molecules ○ They are free to move around- cross the membrane

9. Osmosis  Direction of movement depends on the relative concentration of free water molecules in cytoplasm vs. outside of the cell Free water molecules move from high concentration to low concentration

11. Osmosis  Hypertonic Solution Water moves out of the cell The cell shrinks The fluid outside of the cell has a higher concentration of dissolved particles; lower concentration of free water molecules Free water molecule concentration is higher inside the cell; water will move out to the lower concentration

14. Osmosis  Hypotonic Solution Water moves into the cell The cell swells Fluid outside the cell has fewer dissolved particles; higher concentration of free water molecules Free water molecules inside the cell is lower; water will move into the cell to the lower concentration

17. Osmosis  Isotonic Solution Water moves in and out equally No change in the size of the cell No net water movement Fluid on the inside of the cell has the same concentration as the outside of the cell Diffusion in and out occurs at the same rate

21. Protein Channels  Ions and polar molecules cannot pass through the nonpolar interior of the cell membrane  Use transport proteins (channels)  Does NOT require energy  Down the concentration gradient

23. Ion Channels  Transport protein with a polar pore which allows a specific ion to pass into and out of the cell  Some stay open; some open and close by responding to stimuli

25. Electrical Charge and Ion Transport  Movement of ions are influenced by their charge (positive or negative)  Inside of cell is typically negative Positive ions tend to diffuse into the cell  Movement from the concentration gradient may oppose the movement by electrical charge

26. Facilitated Diffusion  Transport proteins  Does NOT require energy  Down the concentration gradient  Binds to a specific substance on one side of the cell and carries substances across the cell membrane