Membrane Transport: Passive & Active | Endocytosis & Exocytosis | Cell Biology

Summary

A comprehensive overview of cellular transport mechanisms, explaining how cells maintain homeostasis by regulating the movement of molecules through plasma membranes via passive transport, active transport, osmosis, and bulk transport.

Highlights

Plasma Membrane Structure00:00:32

Explains the fluid mosaic model, detailing the structure of phospholipids (hydrophilic heads and hydrophobic tails), the role of cholesterol in regulating fluidity, and the functions of integral and peripheral proteins.

Selective Permeability00:07:47

Discusses how membrane structure influences permeability based on molecule size, charge, and polarity, noting that small nonpolar molecules cross easily while ions and large polar molecules require transport proteins.

Passive Transport00:11:43

Details the process of diffusion down a concentration gradient without the use of cellular energy. Covers simple diffusion, facilitated diffusion, and the role of gated ion channels.

Active Transport00:27:00

Describes how cells use ATP to move substances against their concentration gradient. Explains primary active transport (e.g., sodium-potassium pump) and secondary active transport coupled to electrochemical gradients.

Osmosis and Water Balance00:37:23

Explains the net diffusion of water across semi-permeable membranes via aquaporins, defining osmolarity and the impact of isotonic, hypertonic, and hypotonic solutions on cells.

Bulk Transport00:45:01

Covers endocytosis (pinocytosis, phagocytosis, receptor-mediated) and exocytosis as mechanisms for transporting large particles and cellular waste, including the role of the Golgi apparatus in packaging these materials.