#AP Biology: Membrane Transport - Your Ultimate Review 🚀

Hey there, future AP Bio superstar! Let's break down membrane transport, making sure you're totally confident for the exam. We'll cover facilitated diffusion, active transport, and everything in between. Let's get started!

#Passive Transport: Moving with the Flow 🌊

#What is Passive Transport?

Passive transport is all about moving molecules down their concentration gradient – from an area of high concentration to an area of low concentration. Think of it like rolling a ball downhill; it doesn't require any extra energy input.

Key Concept

Passive transport doesn't require the cell to expend any energy (ATP). It's driven by the natural tendency of molecules to spread out.

#Facilitated Diffusion: When Help is Needed 🤝

Sometimes, molecules can't pass through the phospholipid bilayer on their own, especially if they're charged or polar. That's where facilitated diffusion comes in! It's still passive transport (no ATP needed), but it uses membrane proteins to help molecules cross.

Quick Fact

Facilitated diffusion is still passive transport because molecules move down their concentration gradient. The proteins just make the process easier.

#Why Facilitated Diffusion?

Charged Ions: Like Na+, K+, and Cl- can't pass through the hydrophobic core of the membrane.
Polar Molecules: Molecules like water (H2O) and glucose need help getting through.

#Types of Membrane Proteins

There are two main types of proteins that help with facilitated diffusion:

Channel Proteins:
- Form a hydrophilic channel through the membrane.
- Allow specific molecules or ions to pass through.
- Example: Aquaporins for water transport. 💧
- Gated Ion Channels: Open or close in response to a stimulus (like an electrical signal). Crucial in nerve and muscle cells.
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Facilitated Diffusion