4. Summary: A Head-to-Head Comparison
This table provides a clear summary of the key distinctions between passive and active transport, making it an excellent study guide.
| Feature | Passive Transport | Active Transport |
| Energy Requirement | Does not require cellular energy (ATP). | Requires cellular energy (ATP). |
| Concentration Gradient | Moves molecules down their gradient (from high to low concentration). | Moves molecules against their electrochemical gradient (from low to high concentration). |
| Key Proteins Involved | Ion Channels and Carrier Proteins (Facilitated Diffusion). | Carrier Proteins only. |
| Example Processes | Simple diffusion of O₂, facilitated diffusion of ions, water movement via aquaporins. | Na⁺-K⁺ pump, Glucose symport, ABC transporters pumping out toxins. |