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Transcript
Chapter 5 HSCE: B2.5h Passive Active transport (does not require energy) transport (requires energy) Substances can cross the cell membrane with no energy required. Includes: Diffusion Facilitated (includes Ion Channels) Simple Osmosis Concentration Gradient-the difference in the concentration of molecules across a distance. Substances naturally travel down their concentration gradient (high to low concentration). http://my.hrw.com/sh2/sh07_10/student/fla sh/visual_concepts/60075.htm Diffusion-Movement of molecules from an area of higher concentration to an area of lower concentration In the absence of other influences, diffusion will eventually cause the molecules to be in EQUILIBRIUM SIMPLE DIFFUSION- diffusion across a membrane Cell membranes allow certain molecules to pass through, but not others. Depends on the size and type of molecule. Cell membrane Some molecules are too large or are not soluble in lipids (can’t pass the lipid bilayer). They need the help of CARRIER PROTEINS. Does not require any extra energy to transport the molecules because they are still traveling from higher to lower concentration (passive transport). molecule Cell membrane (lipid bilayer) carrier protein Facilitated Diffusion Another type of passive transport carries ions across the membrane through proteins called ION CHANNELS. Ions: sodium (Na+), potassium (K+), calcium (Ca2+), chlorine (Cl-) Each type of ion channel is usually specific to a certain ion. Some channels are always open, others have “gates”. IONS Ion channel Osmosis-Movement of WATER molecules across a cell membrane from an area of higher concentration to an area of low concentration. Osmosis Passive transport In a solution, a solute (the substance being dissolved) is dissolved in a solvent (substance doing the dissolving). Example: SUGAR (solute) dissolves in WATER (solvent) In cells the solutes are organic molecules and the solvent is water. OSMOSIS: the process by which water molecules diffuse across a cell membrane from an area of higher to lower concentration. Osmosis solute Water molecules Direction of Water movement across the membrane Isotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Hypotonic Solution Hypertonic Solution PLASMOLYSIS CYTOLYSIS Cell can burst Cells shrink away from cell wall, turgor pressure lost 15 The pressure exerted by water inside the cell wall is called TURGOR PRESSURE •When turgor pressure is gained and the cell bursts: CYTOLYSIS •When turgor pressure is lost the cell shrinks away from the cell wall and the plant wilts: PLASMOLYSIS External solution is hypotonic to cytosol: water moves in…cell can burst Plasmolysis External solution is isotonic to cytosol: No net movement External solution is hypertonic to cytosol: water moves out…cell shrinks Isotonic Hypotonic Hypertonic 17 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? 18 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? 19 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at _______________. 20 Active transport moves substances against the concentration gradient (from lower concentration to higher). Pumps This requires energy most often supplied by ATP Sodium-potassium pump Movement in vesicles Move macromolecules and nutrients that are too large to pass the cell membrane or “packs” of small molecules at the same time. Two types Endocytosis Exocytosis Step 1-3: 3 Na+ bind to protein from inside the cell, a phosphate is removed from ATP binding to the carrier protein and turning ATP into ADP. The protein changes shape releasing the 3 Na+ to the outside. Steps 4-6: The protein then picks up 2 K+ from the inside, the phosphate is removed, changing the shape so that it releases the 2 K+ into the cell. sodium potassium pump Sodiumpotassium pump Pumps 3 Sodium ions out of the cell Pumps 2 Potassium ions into the cell This difference in charge is important for the conduction of electrical impulses along nerve cells. Cells ingest (take in) external fluid, macromolecules, and large particles. External materials are enclosed in a “pouch” that pinches off from the cell and becomes a membrane-bound vesicle. Two main types Pinocytosis- transports fluids or solutes Phagocytosis- transports large particles or whole cells. Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” 26 Many unicellular organisms feed by the process of phagocytosis. Certain cells (Phagocytes) in animals use phagocytosis to ingest bacteria and viruses that invade the body. Pinocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle. 28 Process by which a substrate is released from the cell through a vesicle. Homeostasis Is aided by Passive transport Cell transport which includes Active transport Such as Such as Of substance down their Concentration gradient Of substances against their Osmosis Endocytosis Diffusion Exocytosis Facilitated diffusion Which use a Carrier Protein Sodium-potassium pump Three Forms of Transport Across the Membrane Active transport 31