Selective Permeability and Membrane Transport

Vocabulary flashcards covering the selective permeability of the plasma membrane, factors influencing permeability, active transport mechanisms, and forms of passive transport.

Selectively Permeable Barrier

A feature of the cell membrane meaning it allows some substances to pass through it freely, while restricting the passage of other substances.

Lipid Solubility

A factor affecting membrane permeability wherein lipid-soluble substances, such as oxygen and carbon dioxide, can easily pass through the phospholipid bilayer, whereas non-lipid-soluble substances have a harder time crossing.

Size of Molecules

A factor affecting membrane permeability wherein smaller molecules, such as water and urea, can pass through the membrane more easily than larger molecules.

Charge of Molecules

A factor affecting membrane permeability wherein charged molecules, like ions, struggle to pass through the nonpolar interior of the membrane unless specialized transport proteins are present.

Transport Proteins

Specialized proteins embedded in the membrane that enable the cell to actively pump certain molecules in or out against their concentration gradients.

Sodium-Potassium ($Na^+/K^+$) Pump

A specialized membrane transport protein mechanism that utilizes energy from $ATP$ (yielding $ADP$ and phosphate) to actively transport $Na^+$ and $K^+$ ions across the plasma membrane against their concentration gradients.

Passive Transport

The movement of substances across the cell membrane without the cell having to use any of its own energy, moving materials along a concentration gradient from high to low concentration.

Concentration Gradient

A difference in concentration across space or a membrane along which materials move in passive transport, flowing from an area of high concentration to an area of low concentration.

Diffusion

An example of passive transport in which substances move across the cell membrane along a concentration gradient without the expenditure of cellular energy.

Osmosis

An example of passive transport involving the movement of substances across the cell membrane along a concentration gradient without requiring cellular energy.

Facilitated Diffusion

An example of passive transport that moves materials across the cell membrane along their concentration gradient without the use of cellular energy.

Filtration

An example of passive transport in which materials move along a concentration gradient across the cell membrane without the cell needing to expend energy.