Transport Across the Cell Membrane

1. Chapter 4 Transport Across the Cell Membrane

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