Cell Membrane Structure, Passive Transport, and Active Transport

Vocabulary practice flashcards covering cell membrane composition, passive transport mechanisms (diffusion, facilitated diffusion, osmosis), and active transport mechanisms (protein pumps, endocytosis, exocytosis).

Phospholipid Bilayer

A two-layered biological membrane composed of phospholipids where hydrophilic polar heads face outward toward aqueous environments inside and outside the cell, while hydrophobic non-polar tails orient inward together away from water.

Integral Protein

A membrane protein embedded within the cell membrane that spans completely through both layers of the phospholipid bilayer.

Peripheral Protein

A membrane protein located on only one side/surface of the phospholipid bilayer rather than spanning across it.

Hydrophilic Head

The polar, "water-loving" portion of a phospholipid molecule containing a phosphate group that interacts directly with the cell's internal and external aqueous environments.

Hydrophobic Tail

The non-polar, "water-fearing" fatty acid chains of a phospholipid that cluster together in the interior of the bilayer away from water.

Semi-Permeability

A property of the phospholipid bilayer caused by its hydrophobic interior, allowing small, non-polar molecules like $CO_2$ and $O_2$ to pass through freely, while preventing large, charged, or polar molecules from crossing without an integral protein.

Passive Transport

The movement of substances across a cell membrane that requires no cellular energy, relying on a concentration gradient where molecules move constantly, randomly, and away from each other down/with the gradient.

Concentration Gradient

The measurable difference in the concentration of a substance between two adjacent areas.

Diffusion

The net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached and the concentration gradient is eliminated.

Simple Diffusion

The unassisted passive movement of small, non-polar molecules such as $O_2$ and $CO_2$ directly across the phospholipid bilayer.

Facilitated Diffusion

The passive transport of large, charged, or polar molecules down their concentration gradient through specific channel or carrier proteins embedded in the membrane without the use of energy.

Channel Protein

A specific membrane protein that is permanently open, allowing particular polar or charged molecules to pass through the lipid bilayer.

Carrier Protein

A specific membrane protein that binds a substance and changes shape to transport that substance across the membrane.

Osmosis

The net diffusion of water molecules across a semi-permeable membrane.

Active Transport

The cellular process of moving molecules from an area of lower concentration to an area of higher concentration against their concentration gradient, requiring cellular energy in the form of ATP and membrane protein pumps.

Protein Pump

An integral membrane transport protein that utilizes ATP energy to move solutes across the membrane against their concentration gradient, creating or maintaining a concentration difference.

Vesicular Transport

A type of transport using small membrane-bound bubbles (vesicles) to carry large molecules or large groups of molecules into or out of the cell while ensuring the cell membrane remains intact.

Endocytosis

A three-step vesicular transport process that brings substances into the cell: first, the cell engulfs material; second, the membrane seals around it; third, the vesicle pinches off inside the cytoplasm.

Exocytosis

A three-step vesicular transport process that expels materials from the cell: first, a vesicle fuses with the cell membrane; second, a pore opens to the outside; third, the material is released into the external environment.

Equilibrium

The balanced state attained when molecules are uniformly distributed across two regions, completely eliminating the concentration gradient.