Cell Membranes and Transport Vocabulary

50 vocabulary flashcards covering key terms from Topic 4 Cell Membranes and Transport.

Fluid mosaic model

Concept describing the membrane as a dynamic, fluid phospholipid bilayer with embedded, mobile proteins creating a patchwork appearance.

Phospholipid bilayer

Two layers of phospholipids with hydrophobic tails inward and hydrophilic heads outward forming the basic membrane barrier.

Hydrophobic tail

Non-polar fatty-acid end of a phospholipid that repels water and creates the membrane’s non-polar interior.

Hydrophilic head

Polar phosphate–glycerol portion of a phospholipid that interacts with aqueous environments inside and outside the cell.

Cholesterol

Small lipid with a hydrophilic OH head and hydrophobic ring tail that regulates membrane fluidity and stability.

Glycolipid

Membrane lipid covalently bonded to a carbohydrate; functions in cell recognition, self-antigen activity, and membrane stability.

Glycoprotein

Protein with attached carbohydrate chain involved in cell recognition, signalling, adhesion, and as receptors.

Channel protein

Hydrophilic pore within the membrane that allows specific ions or polar molecules to diffuse down their gradient.

Carrier protein

Membrane protein that binds a molecule, changes shape, and transports it across the membrane in facilitated diffusion or active transport.

Cell signalling

Process where cells release ligands that travel to and bind receptors on target cells to trigger specific responses.

Cell recognition

Ability of a cell to identify other cells via surface antigens such as glycoproteins and glycolipids.

Unsaturated fatty acid

Fatty acid containing one or more C=C double bonds; bent shape increases membrane fluidity.

Saturated fatty acid

Fatty acid with no double bonds; straight chains pack tightly, decreasing membrane fluidity.

Membrane fluidity

Measure of how easily lipid and protein molecules move laterally within the membrane.

Membrane stability

Resistance of the membrane to disruption, influenced by cholesterol content, fatty-acid saturation, and temperature.

Passive transport

Movement of substances across membranes without energy input, e.g., diffusion and osmosis.

Simple diffusion

Net movement of molecules from high to low concentration directly through the phospholipid bilayer.

Facilitated diffusion

Passive movement of polar or charged particles across membranes via channel or carrier proteins.

Osmosis

Diffusion of water through a selectively permeable membrane down a water potential gradient.

Water potential

Potential energy of water; tendency for water to move, highest (0) in pure water and lowered by solutes or tension.

Solute potential (ψs)

Component of water potential due to dissolved solutes; always negative except in pure water.

Pressure potential (ψp)

Component of water potential created by physical pressure on a solution; positive when pressure is applied.

Active transport

Energy-requiring movement of molecules against their concentration gradient via carrier proteins and ATP hydrolysis.

Sodium-potassium pump

ATP-driven carrier that exports 3 Na⁺ and imports 2 K⁺ per cycle, maintaining ionic gradients in animal cells.

Endocytosis

Bulk uptake of materials into a cell by invagination of the plasma membrane to form vesicles.

Exocytosis

Bulk export of materials when vesicles fuse with the plasma membrane and release contents outside the cell.

Phagocytosis

Form of endocytosis where large solid particles or cells are engulfed into phagocytic vacuoles.

Pinocytosis

Form of endocytosis involving ingestion of extracellular fluid and dissolved solutes; often called “cell drinking.”

Surface area to volume ratio

Relationship that decreases as objects grow larger, limiting diffusion efficiency in bigger cells.

Second messenger

Intracellular signalling molecule (e.g., cAMP) produced after receptor activation to amplify the signal inside the cell.

G protein

Membrane-associated protein activated by receptors; triggers enzymes that generate second messengers.

Steroid hormone

Hydrophobic hormone derived from cholesterol that crosses membranes and directly alters gene expression in the nucleus.

Nonsteroid hormone

Hydrophilic hormone (protein, peptide, or modified amino acid) that binds membrane receptors and uses second messengers.

Turgid

State of a plant cell with a full vacuole and positive pressure potential; protoplast presses firmly against the cell wall. Full with water

Flaccid

Condition of a plant cell that has lost turgor pressure but has not undergone plasmolysis. Water moves out of cell

Protoplast

The living part of a plant cell—including plasma membrane, cytoplasm, and nucleus—excluding the cell wall.

Gated channel

Channel protein that opens or closes in response to stimuli such as voltage or ligand binding, controlling ion flow.

Cell surface receptor

Membrane protein with a specific binding site that detects extracellular ligands and initiates signalling pathways.

Hydrophobic interior

Non-polar core of the phospholipid bilayer that blocks passage of water-soluble substances.

Phospholipid tail length effect

Longer fatty-acid chains pack tightly and decrease membrane fluidity, whereas shorter chains increase fluidity.