Pathways by which Substances Cross Membranes
Diffusion | Mediated transport | |||
| Through lipid bilayer | Through protein channel | Facilitated diffusion | Active transport | |
| Direction of net flux | High conc to low | High conc to low | High conc to low | Low conc to high |
| Use of integral membrane protein | No | Yes | Yes | Yes |
| Saturatable | No | No | Yes | Yes |
| Chemical specificity | No | Yes | Yes | Yes |
| Energy input required | No | No | No | Yes |
| Examples of substances | O2, CO2, fatty acids | Na+, K+, Ca2+ | Glucose | H+, amino acids, glucose, Na+, K+, Ca2+ |
