Unit 2: Passive vs Active Transport and Tonicity Flashcards

Definition of Tonicity: Tonicity describes the moving of water across a membrane. In the process of osmosis, water moves from a high concentration to a low concentration.
Analytical Priority: When evaluating transport scenarios, it is mandatory to always focus on the concentration of water rather than the solute.
Solute-to-Water Conversion Formula: If the concentration of a solute is provided, the amount of water present must be calculated using the following equation: * $100\% \text{ solution} = \text{solute} + \text{water}$

Passive Transport: * Directional Movement: Substances move from a high concentration to a low concentration. * Concentration Gradient: This movement occurs with or down the concentration gradient. * Energy Requirements: Passive transport utilizes no energy. * Primary Examples: diffusion, osmosis, and facilitated diffusion.
Active Transport: * Directional Movement: Substances move from a low concentration to a high concentration. * Concentration Gradient: This movement occurs against or up the concentration gradient. * Energy Requirements: This process requires energy in the form of ATP (Adenosine Triphosphate). * Primary Examples: protein pump, endocytosis, and exocytosis.

Simple Diffusion: * Mechanism: Substances pass straight through the cell membrane without the assistance of a helper molecule. * Typical Substances: Oxygen ( $O_2$ ) and Carbon dioxide ( $CO_2$ ). * Molecular Characteristics: Small, uncharged molecules.
Facilitated Diffusion via Channel Proteins: * Mechanism: Uses a channel protein to allow specific substances to pass through the membrane. * Typical Substances: Glucose (sugar). * Molecular Characteristics: Large and charged molecules.
Facilitated Diffusion of Water (Osmosis): * Mechanism: Uses a specialized water channel protein. * Specific Protein Helper: The protein responsible for this is called the Aquaporin protein. * Typical Substance: Water ( $H_2O$ ).

Protein Pump / Carrier Proteins: * Mechanism: Uses a carrier protein to move molecules across the membrane. * Directionality: Moves molecules that travel from a low concentration to a high concentration. * Common Examples: * Sodium-Potassium Pump ( $Na^+ - K^+$ Pump). * Proton pump.
Endocytosis: * Mechanism: Uses a vesicle to bring substances into the cell. * Function: Takes large amounts of food or liquid into the cell. * Sub-categories: * Phagocytosis. * Pinocytosis.
Exocytosis: * Mechanism: Uses a vesicle to discharge substances from the cell. * Function: Takes large amounts of food or liquid out of the cell. * Structural Components Involved: Cytoplasm, fluid outside the cell, and the vesicle.