Topic 13: The Plasma Membrane

Vocabulary flashcards covering the structure of the plasma membrane, its components, and the types of transport across it.

Plasma membrane

Semipermeable boundary that separates the inside of the cell from the outside environment and regulates what enters and leaves the cell.

Fluid mosaic model

Model describing the membrane as a mosaic of proteins floating in a fluid phospholipid bilayer; components can move laterally.

Phospholipid bilayer

Two layers of phospholipids forming the core of the membrane with hydrophilic heads facing outward and hydrophobic tails inward.

Amphipathic

Property of having both hydrophilic (polar) and hydrophobic (nonpolar) regions; characteristic of phospholipids.

Hydrophilic head

The polar, water-attracting part of a phospholipid (glycerol + phosphate + often a nitrogen group).

Hydrophobic tail

Nonpolar fatty acid tails of a phospholipid that avoid water and interact to form the bilayer’s core.

Cholesterol (membrane)

Steroid lipid that strengthens membrane, reduces permeability, and helps maintain fluidity, especially at varying temperatures.

Glycoprotein

Protein with attached carbohydrate groups; acts as a recognition molecule to distinguish neighboring cells.

Transport protein

Protein that regulates movement of large, hydrophilic, or ionic molecules across the membrane; includes channels and carriers.

Channel protein

Hydrophilic pore in the membrane that allows specific molecules to pass through quickly.

Carrier protein

Protein that binds a molecule on one side of the membrane and ferries it to the other side; can enable facilitated diffusion or active transport.

Transport proteins categories

Main categories include channel proteins and carrier proteins that aid molecule passage.

Receptor protein

Communication protein activated by external signals to initiate a response inside the cell.

Structural protein

Protein that helps anchor the membrane to the cytoskeleton or extracellular matrix.

Diffusion

Movement of molecules from high to low concentration until equilibrium is reached; no energy required.

Osmosis

Diffusion of water across a semipermeable membrane from higher water concentration to lower.

Isotonic

Solution with equal solute concentration on both sides of a membrane; water movement is balanced.

Hypertonic

Solution with higher solute concentration; water tends to move out of the cell.

Hypotonic

Solution with lower solute concentration; water tends to move into the cell.

Concentration gradient

Difference in solute concentration across space that drives diffusion and osmosis.

Simple diffusion

Diffusion of small, nonpolar molecules directly through the phospholipid bilayer without transport proteins.

Facilitated diffusion

Passive transport that uses transport proteins (channels or carriers) to move molecules down their gradient.

Active transport

Transport of molecules against their concentration gradient, requiring energy (ATP).

ATP

Adenosine triphosphate; energy currency used by cells for active transport.

Turgor pressure

Pressure generated when plant cells swell in hypotonic solutions, pressing the plasma membrane against the cell wall.