Biology 2E Chapter 5: Structure and Function of Plasma Membranes

Vocabulary practice flashcards generated from Biology 2E Chapter 5 lecture notes covering plasma membrane components, fluidity, passive diffusion, active transport pumps, and bulk transport mechanisms.

Plasma Membrane

The selectively permeable boundary that separates the living cell from its surroundings, defines the outer border, and manages what enters and exits.

Fluid Mosaic Model

A model proposed in 1972 by S.J. Singer and G.L. Nicolson describing the plasma membrane as a mosaic of components—phospholipids, cholesterol, proteins, and carbohydrates—that give it a fluid character.

Amphiphilic

Refers to a molecule containing both a hydrophilic (polar) region and a hydrophobic (nonpolar) region, such as a phospholipid.

Phospholipid

The primary component of the plasma membrane, consisting of a glycerol molecule, a polar phosphate head, and two nonpolar fatty acid tails.

Cholesterol

A lipid located within the fatty acid layer of animal cell membranes that acts as a temperature buffer, maintaining appropriate membrane fluidity.

Integral Proteins

Membrane proteins that penetrate through or span across the phospholipid bilayer, having hydrophobic regions aligned with fatty acid tails and hydrophilic regions exposed to water.

Peripheral Proteins

Membrane proteins found exclusively on the inner or outer surfaces of the phospholipid bilayer and not embedded in the central fatty acid layer.

Glycoprotein

A protein attached to a carbohydrate chain on the exterior surface of the plasma membrane, functioning in cell-cell recognition and acting as a receptor.

Glycolipid

A membrane lipid attached to a carbohydrate chain located on the outer surface of the plasma membrane, involved in cell-cell recognition.

Passive Transport

A method of transport across a membrane that requires no expenditure of energy (ATP) by the cell, moving substances down their concentration gradient.

Diffusion

The passive movement of a substance from an area of higher concentration to an area of lower concentration directly across the phospholipid bilayer.

Facilitated Diffusion

Passive transport where substances move down their concentration gradient across a membrane with the aid of transmembrane channel or carrier proteins.

Aquaporin

A specific transmembrane channel protein that is open at all times to allow rapid passage of water molecules across the plasma membrane.

Carrier Proteins

Transmembrane proteins specific to a single substance that bind to that substance, undergo a shape change, and carry it across the membrane.

Osmosis

The diffusion of water across a membrane from an area of higher free water concentration (lower solute concentration) to an area of lower free water concentration (higher solute concentration).

Tonicity

The ability of an extracellular solution to alter the volume of a cell by causing water to enter or leave via osmosis.

Hypertonic Solution

An extracellular solution with a higher solute concentration (osmolarity) relative to the cell cytoplasm, causing water to exit the cell.

Isotonic Solution

An extracellular solution with the same solute concentration (osmolarity) as the cell cytoplasm, resulting in equal movement of water in and out.

Hypotonic Solution

An extracellular solution with a lower solute concentration (osmolarity) relative to the cell cytoplasm, causing water to enter the cell.

Turgor Pressure

The pressure exerted by the plasma membrane against the rigid cell wall in plants when water enters the cell under hypotonic conditions.

Contractile Vacuole

A specialized organelle in freshwater protists (such as paramecia) that collects and pumps excess water out of the cell to maintain osmoregulation.

Active Transport

The movement of ions or molecules across a plasma membrane against a concentration or electrochemical gradient, requiring cellular energy (ATP).

Electrochemical Gradient

A combined gradient of concentration and electrical charge across a biological membrane.

Primary Active Transport

Active transport that directly uses energy from ATP hydrolysis to move ions or molecules against their concentration gradient.

Secondary Active Transport

Active transport that uses the electrochemical gradient created by primary active transport to move a secondary substance against its concentration gradient.

Uniporter

A carrier protein that transports a single specific molecule or ion in one direction across the plasma membrane.

Symporter

A carrier protein that transports two different molecules or ions across the plasma membrane in the same direction.

Antiporter

A carrier protein that transports two different molecules or ions across the plasma membrane in opposite directions.

Sodium-Potassium Pump

An electrogenic antiporter pump that uses energy from 1 ATP molecule to transport 3 $Na^+$ ions out of the cell and 2 $K^+$ ions into the cell.

Bulk Transport

An active transport process that uses energy to move particles or large quantities of molecules across the plasma membrane enclosed within vesicles.

Endocytosis

A form of bulk active transport where the cell takes in external materials by engulfing them within invaginations of the plasma membrane.

Phagocytosis

A targeted type of endocytosis commonly referred to as cellular eating, where the plasma membrane surrounds a large particle or invader and engulfs it into a vacuole.

Pinocytosis

A type of endocytosis known as cellular drinking, where the plasma membrane invaginates to take in fluid and dissolved solutes from the extracellular space.

Receptor-Mediated Endocytosis

A selective form of endocytosis triggered when specific extracellular target molecules bind to complementary receptor proteins on the external membrane surface.

Exocytosis

A bulk transport process where membrane-bound vesicles containing materials fuse with the plasma membrane to release their contents outside the cell.