Topic 13 – The Plasma Membrane: Key Vocabulary

Vocabulary flashcards summarizing major terms and definitions from Topic 13: The Plasma Membrane.

Plasma Membrane

A semipermeable boundary composed primarily of a phospholipid bilayer that separates a cell’s interior from its external environment and regulates material exchange.

Fluid Mosaic Model

Concept that describes the plasma membrane as a fluid phospholipid bilayer with proteins and other molecules embedded like a mosaic; first proposed by Singer and Nicholson (1972).

Phospholipid Bilayer

Two layers of amphipathic phospholipids whose hydrophilic heads face outward toward water and hydrophobic tails face inward, forming the membrane’s core.

Phospholipid

An amphipathic lipid consisting of a hydrophilic phosphate head and two hydrophobic fatty-acid tails; main structural molecule of membranes.

Amphipathic Molecule

A molecule containing both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, e.g., phospholipids.

Hydrophilic

Water-loving; property of molecules or regions that readily interact with water.

Hydrophobic

Water-fearing; property of molecules or regions that repel water and mix with non-polar substances.

Cholesterol

Steroid lipid inserted in animal cell membranes that adds strength and regulates fluidity and permeability, especially at higher temperatures.

Transport Protein

Membrane protein that assists the movement of ions or large/polar molecules across the plasma membrane.

Recognition Protein (Glycoprotein)

Membrane protein, often with attached carbohydrates, that enables a cell to identify and distinguish neighboring cells.

Structural Protein

Membrane-associated protein that anchors the cell to the extracellular matrix or stabilizes other membrane proteins.

Communication Protein

Membrane protein (e.g., receptor) that receives external signals and initiates cellular responses.

Receptor Protein

A communication protein that binds specific signaling molecules (ligands) outside the cell, triggering internal reactions.

Semipermeable

Describes a membrane that allows some substances to cross while restricting others.

Selective Permeability

Characteristic of the plasma membrane to regulate passage of different molecules based on size, charge, and polarity.

Diffusion

Passive movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is achieved.

Concentration Gradient

Difference in the concentration of a substance between two regions; drives diffusion.

Equilibrium

State at which the concentration of a substance is equal throughout a space, resulting in no net diffusion.

Osmosis

Diffusion of water across a semipermeable membrane from an area of higher water (lower solute) concentration to lower water (higher solute) concentration.

Isotonic Solution

Solution with the same solute concentration as another; produces no net movement of water across a membrane.

Hypertonic Solution

Solution with a higher solute concentration than another; draws water out of a cell placed in it.

Hypotonic Solution

Solution with a lower solute concentration than another; causes water to flow into a cell placed in it.

Turgor Pressure

Pressure exerted by water inside a plant cell against the cell wall, providing structural rigidity.

Passive Transport

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

Facilitated Diffusion

Passive transport in which molecules move down their concentration gradient through protein channels or carrier proteins.

Active Transport

Energy-requiring process in which transport proteins move molecules against their concentration gradient using ATP.

Carrier Protein

Transport protein that binds a specific molecule, changes shape, and ferries it across the membrane; can mediate facilitated diffusion or active transport.

Channel Protein

Hydrophilic pore in the membrane that allows specific ions or polar molecules to pass quickly, usually by facilitated diffusion.

ATP (Adenosine Triphosphate)

Cellular energy currency used to power active transport and many other biological processes.

Proton Pump

Active-transport protein that uses ATP to move hydrogen ions (protons) across a membrane, establishing an electrochemical gradient.