Cell Transport Mechanisms

Vocabulary flashcards covering key terms related to transport across cell membranes.

Phospholipid bilayer

The double layer of phospholipids that forms the fundamental structure of the cell membrane and acts as a selective barrier.

Passive transport

Movement of substances across a membrane without energy expenditure, driven by a concentration gradient.

Active transport

Energy-requiring movement of substances across a membrane against their concentration gradient, typically using ATP.

Simple diffusion

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

Facilitated diffusion

Passive transport in which molecules move down their gradient with the help of membrane proteins such as channels or carriers.

Osmosis

Diffusion of water through a semipermeable membrane from an area of high water (low solute) concentration to low water (high solute) concentration.

Concentration gradient

A difference in the amount of a substance across space or a membrane; drives diffusion processes.

Kinetic energy (of molecules)

Intrinsic molecular motion that allows particles to diffuse passively without cellular energy.

Channel protein

Transmembrane protein that forms a hydrophilic pore allowing specific ions or molecules to pass.

Carrier protein

Membrane protein that binds a substance, changes shape, and transports it across the membrane.

Aquaporin

Channel protein specialized for rapid water transport across cell membranes.

GLUT

A glucose transporter that mediates facilitated diffusion of glucose into cells.

Isotonic solution

An external solution with the same solute concentration as the cell interior; results in no net water movement.

Hypotonic solution

Solution with a lower solute concentration than the cell; water enters the cell, causing it to swell.

Hypertonic solution

Solution with a higher solute concentration than the cell; water leaves the cell, causing it to shrink.

Cytolysis

Destruction of a cell by swelling and bursting in a hypotonic environment.

Plasmolysis

Shrinking of the cytoplasm away from the cell wall when a plant cell is placed in a hypertonic solution.

Sodium-potassium pump

Active transport protein that uses ATP to move 3 Na⁺ out of and 2 K⁺ into the cell, establishing ion gradients.

Membrane potential

Electrical potential difference across the cell membrane created by ion gradients, especially via the Na⁺/K⁺ pump.

Exocytosis

Active transport process in which vesicles fuse with the plasma membrane to release materials outside the cell.

Endocytosis

Active uptake of materials into a cell by forming vesicles from the plasma membrane.

Pinocytosis

"Cell drinking"; endocytosis of dissolved molecules in fluid droplets into small vesicles.

Phagocytosis

"Cell eating"; engulfment of large particles or microorganisms into vesicles.

Receptor-mediated endocytosis

Selective uptake where ligands bind to membrane receptors that trigger vesicle formation.

Semipermeable membrane

Barrier that permits certain molecules (e.g., water) to pass while restricting others.

Solvent

Substance, typically liquid like water, that dissolves solutes to form a solution.

Solute

Substance dissolved in a solvent; its concentration influences osmotic movement.

Equilibrium (diffusion)

State in which concentrations are equal across a membrane, resulting in no net diffusion.

ATP (adenosine triphosphate)

Primary energy currency of the cell, used to power active transport and other processes.

Membrane transport proteins

General term for channel and carrier proteins that facilitate movement of substances across cell membranes.