Topic 13 – Plasma Membrane & Transport

Vocabulary flashcards covering major terms related to the plasma membrane structure, components, and transport mechanisms.

Plasma Membrane

Selectively permeable boundary of the cell that controls substance movement and enables cell-to-cell communication.

Selective Permeability

Ability of a membrane to allow some molecules to cross more easily than others while blocking the rest.

Phospholipid

Lipid with a phosphate head and two fatty acid tails; principal building block of cell and organelle membranes.

Amphipathic

Describes a molecule possessing both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Hydrophilic Head

Polar glycerol-phosphate portion of a phospholipid that interacts with aqueous environments.

Hydrophobic Tail

Non-polar fatty acid chains of a phospholipid that avoid water and face inward in membranes.

Phospholipid Bilayer

Two layers of phospholipids with heads out and tails in, forming the core of biological membranes.

Fluid Mosaic Model

Concept that membranes are fluid, dynamic structures containing a mosaic of lipids, proteins, and other molecules.

Membrane Fluidity

Lateral movement of phospholipids and proteins within the bilayer; regulated by fatty acid saturation and cholesterol.

Cholesterol

Hydrophobic sterol inserted between phospholipids in animal membranes to stiffen, reduce permeability, and modulate fluidity.

Transport Protein

Membrane protein that facilitates movement of specific molecules across the membrane.

Channel Protein

Transport protein forming a hydrophilic tunnel through which certain ions or small molecules pass.

Carrier Protein

Transport protein that binds a specific molecule, changes shape, and moves it across the membrane.

Recognition Protein (Glycoprotein)

Membrane protein with attached sugars that allows cells to identify and interact with one another.

Receptor

Membrane protein that binds external signals and initiates cellular responses.

Concentration Gradient

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

Simple Diffusion

Passive movement of small, non-polar molecules directly through the bilayer from high to low concentration.

Passive Transport

Energy-free movement of substances across membranes; includes simple diffusion, osmosis, and facilitated diffusion.

Osmosis

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

Isotonic Solution

Two solutions with equal solute concentration; results in no net water movement.

Hypotonic Solution

Solution with lower solute concentration relative to another; water enters the cell placed in it.

Hypertonic Solution

Solution with higher solute concentration relative to another; water exits the cell placed in it.

Turgid

Firm, swollen state of a plant cell in a hypotonic environment due to water uptake.

Flaccid

Limp state of a plant cell in a hypertonic environment after losing water.

Lyse

To burst; what can happen to an animal cell placed in an extremely hypotonic solution.

Facilitated Diffusion

Passive transport of large, polar, or charged molecules through channel or carrier proteins down their gradient.

Active Transport

ATP-powered movement of substances through transport proteins against their concentration gradient.

ATP (Adenosine Triphosphate)

Cellular energy molecule hydrolyzed to drive active transport and other energy-requiring processes.

Equilibrium

State reached when concentrations of a substance are uniform, resulting in no net diffusion.

Saturated vs. Unsaturated Fatty Acids

Straight-chained (no double bonds) tails vs. kinked (double bonds) tails; unsaturated tails increase membrane fluidity.