Cell Membrane & Transport Vocabulary

Vocabulary flashcards covering the structure and transport functions of the plasma membrane.

Plasma Membrane (Cell Membrane)

A phospholipid bilayer that encloses the cytoplasm and controls what enters and exits the cell.

Phospholipid Bilayer

Two layers of phospholipids with hydrophilic phosphate heads facing outward and hydrophobic fatty-acid tails facing inward.

Hydrophobic Tails

Fatty-acid chains of a phospholipid that repel water and face the interior of the bilayer.

Hydrophilic Heads

Phosphate groups of a phospholipid that attract water and face the aqueous environments inside and outside the cell.

Semi-Permeable

Property of the membrane that allows some substances to pass through while blocking others based on size or polarity.

Fluid Mosaic Model

Describes the plasma membrane as a dynamic, flexible structure with a mosaic of proteins embedded in or attached to a fluid lipid bilayer.

Cholesterol (in membranes)

Steroid molecule that modulates membrane fluidity and decreases permeability to small water-soluble molecules.

Protein Receptors

Membrane proteins (often glycoproteins or glycolipids) that bind specific molecules and initiate cellular responses.

Passive Transport

Movement of substances across a membrane without energy input; includes diffusion, osmosis, and facilitated diffusion.

Diffusion

Net movement of particles from high to low concentration down their concentration gradient until equilibrium is reached.

Equilibrium (in diffusion)

State in which there is no net movement of particles because concentrations are equal or nearly equal.

Osmosis

Net movement of water across a semi-permeable membrane from regions of low solute concentration to regions of high solute concentration.

Hypotonic Solution

External solution with lower solute concentration than the cell, causing water to enter the cell.

Hypertonic Solution

External solution with higher solute concentration than the cell, causing water to leave the cell.

Isotonic Solution

Solution with solute concentration equal to that of the cell, resulting in no net water movement.

Active Transport

Energy-requiring (ATP-dependent) process that moves molecules against their concentration gradient.

Concentration Gradient

Difference in the concentration of a substance across a space or membrane that drives diffusion.