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Principles of Diffusion and Cellular Transport
Diffusion Fundamentals:
Definition: Diffusion is the process by which particles move from an area of high concentration to an area of low concentration, spreading out evenly in available space.
Concentration Gradient: This is a region where the density of a chemical substance increases or decreases. Particles will naturally move down this gradient from high to low concentration.
Equilibrium: When concentrations become equal across spaces, equilibrium is reached, and no net diffusion occurs.
Types of Cellular Transport
Passive Transport:
Mechanism: Substances move across the cell membrane without the cell expending energy, known as passive transport.
Diffusion: A key type of passive transport, important for importing nutrients and exporting wastes.
Active Transport:
Energy Requirement: The cell must expend energy (usually ATP) to move substances against their concentration gradient.
Function: Allows the cell to maintain concentration gradients that differ from their surroundings, crucial for various cellular functions.
Vesicle Transport
Formation and Function: Membranes within and around the cell can form vesicles—small sacs made of membrane material—that help import and export large molecules.
Types:
Exocytosis: The process where cells secrete molecules via the fusion of vesicles with the plasma membrane.
Endocytosis: The process where cells intake molecules by vesicle fusion with the plasma membrane.
Phagocytosis: A form of endocytosis where the cell engulfs solid particles into a food vacuole, which then fuses with lysosomes for digestion.
Pinocytosis: Involves the ingestion of extracellular fluids through small vesicles.
Integrated Systems
Endomembrane System Cooperation: The plasma membrane works closely with the endomembrane system (including the endoplasmic reticulum and Golgi apparatus) to regulate material transport via vesicles.
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