Semi-permeability

The property of membranes that restricts the movement of hydrophilic molecules due to the non-polar lipid bilayer.

Selectivity

The ability of integral membrane proteins to regulate the transport of hydrophilic molecules by adopting 'open' or 'closed' conformations.

Passive Transport

Movement of molecules across the membrane along a concentration gradient without the expenditure of energy (ATP).

Active Transport

Movement of molecules against a concentration gradient that requires energy (ATP) and transport proteins.

Simple Diffusion

The net movement of small, lipophilic molecules across a membrane from high to low concentration until equilibrium is reached.

Facilitated Diffusion

Transport of large or charged molecules across a membrane with the assistance of membrane proteins.

Osmosis

The net movement of free water molecules across a semi-permeable membrane from low solute concentration to high solute concentration.

Hypertonic Solution

A solution with a relatively higher solute concentration that causes a cell to lose water via osmosis (resulting in crenation).

Hypotonic Solution

A solution with a relatively lower solute concentration that causes a cell to gain water via osmosis (resulting in cell swelling or lysis).

Isotonic Solution

A solution with the same solute concentration that maintains a constant water level in cells.

Aquaporins

Integral proteins in multicellular organisms that serve as selective water channels, facilitating faster water transport in response to solute concentration changes.

Contractile Vacuoles

Organelles in unicellular organisms that expel excess water to regulate water levels.

Diffusion

The process by which molecules spread from areas of high concentration to areas of low concentration.

Concentration Gradient

The difference in the concentration of a substance between two areas; molecules move from high to low concentration.

Endocytosis

The process by which cells engulf materials from their environment by folding the cell membrane around them.

Exocytosis

The process by which cells expel materials to the outside by vesicles fusing with the cell membrane.

Dynamic Equilibrium

A state in which there is continuous movement but no overall change in concentration of substances.

Membrane Potential

The voltage difference across a cellular membrane that is critical for the function of neurons and muscle cells.

Ion Channels

Protein structures that allow the selective passage of ions across the cellular membrane.

Crenation

The process where cells lose water in a hypertonic solution, causing them to shrink.

Plasmolysis

The contraction of the cell membrane away from the cell wall in plant cells due to loss of water in a hypertonic solution.

Turgor Pressure

Pressure from the fluid inside the central vacuole of plant cells that helps maintain cell shape.