Cell Transport

Exocytosis: Releasing Substances Out00:06:35

Exocytosis is the reverse of endocytosis, where molecules exit the cell. This process is used to remove waste and release important materials made by the cell, such as carbohydrates for plant cell wall formation.

Introduction to Cell Membranes and Homeostasis00:00:08

All cells contain genetic material, cytoplasm, and ribosomes, but eukaryote cells also have membrane-bound organelles. Cells need to control what goes in and out to maintain a stable internal environment (homeostasis), a crucial function of the cell membrane.

The Cell Membrane and Simple Diffusion00:01:05

The cell membrane is a phospholipid bilayer with polar heads and nonpolar tails. Small non-polar molecules like oxygen and carbon dioxide can pass directly through it via simple diffusion. This is a form of passive transport, moving molecules from high to low concentration without energy.

Facilitated Diffusion with Transport Proteins00:02:32

The cell membrane also contains transport proteins that facilitate the movement of larger or polar molecules. These proteins can act as channels or change shape to help molecules like charged ions, glucose, and water (through aquaporins) pass. This is facilitated diffusion, another type of passive transport moving with the concentration gradient without energy.

Active Transport and ATP00:03:57

Active transport moves molecules against their concentration gradient (from low to high concentration), which requires energy, typically from ATP. ATP, adenosine triphosphate, releases a lot of energy when its last phosphate bond is broken, powering transport proteins. The sodium-potassium pump is a key example of active transport.

Endocytosis: Bringing Substances In00:05:12

Endocytosis is a type of active transport where the cell membrane engulfs large molecules, forming vesicles to bring them inside. There are different types: phagocytosis (like amoebas engulfing food), receptor-mediated endocytosis (selective intake), and pinocytosis (taking in fluids).