Rank the rate of transmembrane diffusion of the following...

Key Concepts

Charge and Ionization

The presence of a charge on a molecule, or its ionization state, greatly affects its ability to diffuse through the membrane. Charged and polar molecules interact unfavorably with the hydrophobic lipid core, resulting in slower diffusion rates compared to non-polar molecules.

Molecular Size

The size of a molecule significantly affects its diffusion rate across membranes; smaller molecules generally diffuse faster because they encounter less resistance when passing through the lipid bilayer. Larger molecules may require transport proteins or channels due to their inability to passively diffuse through the membrane.

Concentration Gradient

The concentration gradient is the difference in the concentration of a substance between two regions. A steeper gradient increases the driving force for diffusion, resulting in a higher rate of movement across the membrane according to the principles described by Fick's law.

Passive Diffusion

Passive diffusion is the movement of substances across a membrane without the aid of transport proteins, driven by the concentration gradient. This process relies on the inherent permeability of the membrane to the substance and does not require cellular energy, meaning that substances naturally move from an area of higher concentration to one of lower concentration.

Lipid Solubility

Lipid solubility is a critical factor influencing membrane permeability because the plasma membrane is primarily composed of a lipid bilayer. Compounds that are more lipid-soluble can more easily partition into the hydrophobic core of the membrane, thereby diffusing more rapidly compared to compounds that are hydrophilic.

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