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Cell Membrane Review Functions – Provides boundary for cell – Selectively Permeable: only allows certain things to pass through. “Picky” Ex: Window screen – Maintains homeostasis: balance within the cells Cell Membrane Structure vs. Function – Membrane is a phospholipid bilayer – Phospholipids: two sided molecule with a head that loves (hydrophilic) and a tail that repels (hydrophobic) water – Embedded Proteins: “club bouncers” Decide who goes in & out Markers for recognition TYPES OF TRANSPORT Passive Transport: -Uses No Energy -Movement from high concentration to low concentration Active Transport: – – Uses Energy (ATP) Movement against the concentration gradient (from low concentration to high concentration) Passive Transport Diffusion = movement of molecules from high concentration to low concentration Passive Transport Osmosis = movement (or diffusion) of water from area of high concentration to low concentration Higher Concentration of Water Lower Concentration of Water (Water molecules) (Sugar molecules) HYPO/HYPER/ISO HYPOTONIC: •Concentration of solute is lower outside cell than inside cell, meaning more water outside cell •Water will move INTO cell causing it to SWELL •Animal cells could rupture if the cell takes in too much water •Causes TURGOR PRESSURE in plant cells (more support) HYPERTONIC: •Concentration of solute is higher outside the cell and lower inside cell, meaning less water outside •HYPERTONIC means “above strength” •H2O rushes OUT of cell causing it to shrivel •Results in PLASMOLYSIS in plants (wilting) ISOTONIC: Concentration outside the cell is the same as the inside of the cell for both water and solute ISO- means “equal to” or “same” Movement into cell = movement out of cell; cell does not change. Special Types of Passive Transport Facilitated Diffusion = diffusion through protein tunnels to help larger molecules (like sugar) cross the membrane. Facilitated means “assisted”. Still passive. No energy. Active Transport Movement against the concentration gradient. Molecules will move from an area of low concentration to an area of high concentration. Requires cell energy in the form of ATP (Adenosine Triphosphate) and protein pumps Example - Sodium-Potassium Pump: Protein that actively transports sodium and potassium ions into or out of the cell. Necessary for your nervous system. More Active Transport Endocytosis = the active process by which cells take in particles using vessicles; into the cell – Pinocytosis = drinking action, used for small particles or water – Phagocytosis = devouring action, used for large particles like food Exocytosis = the active process by which cells remove wastes and large particles through vessicles; exit the cell