Cell Membrane Transport Overview

Overview

This lecture covers how substances move across the cell membrane, focusing on the differences between passive and active transport.

Substances cross the cell membrane using either passive transport (no energy required) or active transport (energy required).
The main distinction is that active transport uses cellular energy, often in the form of ATP, while passive transport does not.

Passive transport relies on the kinetic energy of molecules and does not require extra energy input.
Diffusion is the process by which molecules move from an area of high concentration to low concentration.
Temperature reflects the kinetic energy of molecules; higher temperatures mean more kinetic energy and movement.
Concentration is the amount of solute particles in a given volume of solution.
Molarity measures concentration as moles of solute per liter of solution.
Molecules move naturally down their concentration gradient (from high to low concentration) during diffusion.

Simple diffusion: Molecules like O₂ and CO₂ move directly through the cell membrane without help.
Facilitated diffusion: Molecules move down their concentration gradient via a protein helper, either through channels or carriers.
Channels and carriers assist substances that cannot cross the membrane unassisted.

Active transport moves substances against their concentration gradient, requiring energy input.
Always uses a carrier protein to transport substances.
Types include primary active transport and secondary active transport (detailed in a future section).
Vesicular transport (endocytosis and exocytosis) is another form of active transport that also requires energy but is not carrier-based.

Passive Transport — Movement of substances across the membrane without energy input.
Active Transport — Movement of substances against a concentration gradient, requiring energy.
Diffusion — Movement of particles from high to low concentration.
Concentration Gradient — Difference in concentration between two areas.
Molarity — Moles of solute per liter of solution.
Simple Diffusion — Direct movement of molecules through the membrane.
Facilitated Diffusion — Movement through membrane proteins (channels or carriers).
Carrier Protein — Protein that transports specific substances across the membrane.
Vesicular Transport — Movement into or out of the cell by vesicles (endocytosis/exocytosis).