BC Biology 12: Section 3.5 - The Permeability of the Plasma Membrane

Comprehensive vocabulary flashcards covering Section 3.5: The Permeability of the Plasma Membrane, detailing passive and active transport, osmosis, tonicity, and bulk transport mechanisms.

Selectively Permeable

The property of the plasma membrane that allows the passage of only certain molecules into and out of the cell.

Concentration Gradient

A difference in the concentration of a substance across a distance or membrane; movement "down" is from high to low concentration, whereas movement "up" or "against" is from low to high concentration.

Diffusion

The passive movement of molecules down their concentration gradient (from higher to lower concentration) without requiring chemical energy (ATP), influenced by temperature, pressure, and molecule size.

Solute

A substance that is dissolved in a solvent to form a solution.

Solvent

The liquid medium or dissolving agent (such as water) that dissolves a solute to form a solution.

Osmosis

The diffusion of water molecules across a selectively permeable membrane toward an area of lower water concentration (higher solute concentration).

Tonicity

A term referring to the osmotic pressure of a solution relative to that inside a cell.

Osmotic Pressure

The pressure that develops across a selectively permeable membrane as a result of differences in tonicity between solutions.

Isotonic Solution

A solution that has the same concentration of solute and solvent as the fluid inside the cell, resulting in no net movement of water.

Hypotonic Solution

A solution that has a lower concentration of solute (higher water concentration) than the inside of the cell, causing water to enter the cell.

Hypertonic Solution

A solution that has a higher concentration of solute (lower water concentration) than the inside of the cell, causing water to leave the cell.

Lysis

The bursting of an animal cell that occurs when water enters the cell in a hypotonic solution.

Crenation

The shriveling of an animal cell that occurs when water leaves the cell in a hypertonic solution.

Turgor Pressure

The internal hydrostatic pressure that develops against the cell wall when a plant cell's central vacuole fills with water in a hypotonic solution.

Plasmolysis

The shrinking of cytoplasm away from the cell wall in a plant cell as the central vacuole loses water in a hypertonic solution.

Carrier Proteins

Membrane-spanning proteins that specifically bind to and transport particular molecules across the plasma membrane during facilitated transport and active transport.

Facilitated Transport

The passive transport of specific molecules down their concentration gradient using carrier proteins or channels, requiring no ATP.

Active Transport

The movement of substances across the plasma membrane against their concentration gradient using carrier proteins (pumps), requiring chemical energy in the form of ATP.

Sodium-Potassium Pump

A carrier protein pump that uses ATP to transport three sodium ions ($3\,\text{Na}^+$) to the outside of the cell and two potassium ions ($2\,\text{K}^+$) to the inside of the cell, maintaining a negative charge inside relative to outside.

Bulk Transport

Energy-dependent, membrane-assisted transport in which macromolecules are moved into or out of a cell by vesicle formation.

Exocytosis

A form of bulk transport in which an intracellular vesicle fuses with the plasma membrane to secrete substances (such as neurotransmitters, hormones, or digestive enzymes) outside the cell.

Endocytosis

A form of bulk transport in which the cell takes in substances by folding the plasma membrane inward and pinching it off to form an intracellular vesicle.

Phagocytosis

A type of endocytosis ("cell eating") in which the material being taken in is large, such as a food particle or another cell, forming a vacuole that fuses with a lysosome.

Pinocytosis

A type of endocytosis ("cell drinking") in which the plasma membrane forms vesicles around liquids or very small particles such as polypeptides.

Receptor-Mediated Endocytosis

A selective type of pinocytosis that uses receptor proteins embedded in coated pits to bind specific molecules, which then pinch off into coated vesicles.