🧫 Membrane Permeability Explorer

✓
Small Nonpolar
O₂, N₂, CO₂, Steroids
Freely cross
~
Small Polar
H₂O, NH₃
Limited passage
✗
Ions & Large Polar
Na⁺, K⁺, Glucose
Need channels

The nonpolar hydrocarbon tails of phospholipids prevent ions and polar molecules from crossing. Hydrophilic substances require embedded channels and transport proteins. Passive transport moves molecules from high to low concentration without energy input.

PEEBEDU

Membrane Permeability Explorer

Molecules

Transport Channels

Temperature

(Higher = faster & more permeable)

Concentrations
Extracellular | Cytosol
O₂: 0 | 0
N₂: 0 | 0
CO₂: 0 | 0
Steroid: 0 | 0
Water: 0 | 0
Glucose: 0 | 0
Na⁺: 0 | 0
K⁺: 0 | 0
Protein: 0 | 0
Channels: None active
Key:
O₂ (Sm, NP)
N₂ (Sm, NP)
CO₂ (Sm, NP)
Steroid (Sm, NP)
Water (Sm, P)
Glucose (Lg, P)
Na⁺ (Ion)
K⁺ (Ion)
Protein (VLg, P)

Test Your Understanding

1. Which type of molecule can pass through the phospholipid bilayer most easily?
2. Which property of the phospholipid bilayer makes it selectively permeable?
3. Why do ions like Na⁺ and K⁺ require channel proteins to cross the membrane?
4. How do large polar molecules like glucose typically cross the cell membrane?