Cell Transport

Types of Transport Across Cell Membrane Passive Transport Active Transport Cell doesn’t need energy Moving molecules from HIGH to LOW concentrations Three types Cell does use energy Moving molecules from LOW to HIGH concentrations Three types

Passive Transport Passive transport—the movement of molecules across a cell membrane without energy input from the cell High → Low Movement Concentration gradient—the difference in the concentration of a substance from one location to another

Diffusion Diffusion—the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration Random movement through the membrane Goes with the concentration gradient (HIGH → LOW) Example: gas exchange in lungs, gas exchange between cells and blood

Facilitated Diffusion Facilitated diffusion—the diffusion of molecules across a membrane through transport proteins Movement of charged particles and/or larger molecules Uses channel or carrier proteins Also moves with the concentration gradient Example: movement of glucose in the cell

Osmosis Osmosis—diffusion of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration Movement of water molecules only

Effect of Osmosis on Cells Water moves across cell membrane freely thus cells can’t control this movement Three conditions

Result: Water moves out of the cell and the cell shrinks Hypertonic—the concentration of solute is higher outside the cell than inside the cell Result: Water moves out of the cell and the cell shrinks Isotonic—the concentration of solute outside the cell are equal to the concentration of solutes in the cell Result: Water moves equally in both directions and the cell remains the same size Hypotonic—the concentration of solute is lower outside the cell than inside the cell Result: Water moves into the cell and the cell swells

Active transport Low → High Movement Active transport— movement of molecules across a membrane from a region of lower concentration to a region of higher concentration Requires energy from the cell

Protein Pumps A transport protein that moves ions across the membrane with the use of energy Requires the protein to change shape Example: Sodium-Potassium Pump

Endocytosis Endocytosis—the process of taking liquids or fairly large molecules into a cell by engulfing them in a membrane Using the energy cell membrane folds in around the molecule Vesicle combines with lysosome Two types: Phagocytosis—“cell eating” Pinocytosis—“cell drinking” Example: white blood cells eating bacteria

Exocytosis Exocytosis—the release of substances from the cell by the fusion of a vesicle with the membrane Opposite of endocytosis Cell changes shape using energy Example: waste and hormones released from a cell

References Most information from Biology, McDougal Littell (2008)