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Transcript
DIFFUSION, OSMOSIS, AND THE CELL MEMBRANE Structure and Function of Cell Membrane Structure – phospholipid bilayer embedded with protein pumps cells want to maintain equilibrium selectively regulates passage of substances in and out of cell How do things pass through the cell membrane? Through passive transport: no additional energy required Three types small molecules such easily pass through via simple diffusion large molecules (starch) require use of protein pumps for facilitated diffusion Water passes through the cell membrane via osmosis Simple Diffusion Simple diffusion is process in which molecules intermingle as a result of kinetic energy all molecules are in constant motion and continually spreading apart Simple diffusion occurs because of a concentration gradient A concentration gradient exists when one area is more or less concentrated than another. molecules move from an area of high to low concentration, aka simple diffusion Example: Tea Bag or sugar cube in water Let's intracellular circulation – movement of materials within a cell occurs through diffusion see diffusion in action (I am a link!) Facilitated Diffusion Transport of substances across the cell membrane from higher concentrations to areas of lower concentration through means protein pump No energy required Let’s see facilitated diffusion in action (I am a link!) OSMOSIS Diffusion of water is known as osmosis water moves via kinetic energy from a less salty/sugary solution (lower solute concentration) to a more salty/sugary solution (higher solute concentration) in order to dilute out the salt/sugar if too much water builds up inside a membrane, osmotic pressure results if osmotic pressure is too high, the cell can burst/lyse Let’s see osmosis in action (I am a link!) Osmosis and Cells Whether there is net movement of water into or out of the cell and which direction it moves depends on whether the cell’s environment is isotonic, hypotonic, or hypertonic. Tonicity: is a measure of the osmotic (water) pressure gradient of two solutions separated by a semipermeable membrane. Hypertonic refers to a higher concentration Hypotonic refers to a lower concentration Isotonic refers to equal concentrations Tonicity and cells: Cells in an Isotonic Solution When two environments are isotonic, the concentration of dissolved solutes is the same in both of them. When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell. Tonicity and cells: Cells in a Hypertonic Solution Greek "hyper," = over, and "tonos," = stretching. In a hypertonic solution the concentration of solutes is greater than that of the concentration in a cell. If concentrations of solutes are greater outside the cell, the concentration of water outside is correspondingly lower. As a result, water inside the cell will flow outwards to attain equilibrium, causing the cell to shrink. As cells lose water, they lose the ability to function or divide. Tonicity and cells: Cells in a Hypotonic Solution Greek "hypo,"=under, and "tonos,"=stretching. In a hypotonic solution the concentration of solutes is less than that of a cell. When concentrations are less outside the cell than inside, the concentration of water outside is correspondingly greater outside the cell. When a cell is in hypotonic conditions, there is net water movement into the cell. Cells without walls will swell and may burst (lyse) if excess water is not removed from the cell. Cells with walls often benefit from the turgor pressure that develops in hypotonic environments. Active Transport movement of particles with the use of energy other than kinetic sometimes active transport can move molecules from an area of low to high concentration (against the gradient) Two Types of Active Transport First Type: Primary Active Transport Often uses ATP (the cell’s energy) involves protein molecules in the cell membrane that act as carriers aiding in transportation Two Types of Active Transport Second type: ENDOCYTOSIS Phagocytosis (cell eating) – white blood cells that keep the body healthy by engulfing foreign pathogens Membrane folds in around large molecules so they can be taken in by the cell resulting in a vacuole containing the molecule Pinocytosis (cell drinking) – fluids containing large molecules such as DNA or proteins are taken into the cell in the same manner Putting it all together!