Cellular Transport Mechanisms, Membrane Dynamics, and Compartmentalization

Comprehensive vocabulary flashcards covering passive and active transport, membrane potentials, osmosis, tonicity, water potential equations, and cellular compartmentalization as presented in the lecture.

Passive Diffusion

The movement of small, nonpolar molecules directly through the lipid bilayer without the assistance of transport proteins or cellular energy.

Facilitated Diffusion

A form of passive transport aided by membrane proteins, allowing molecules that cannot directly cross the lipid bilayer (such as small charged molecules or larger volumes of water) to move down their concentration gradient without energy.

Aquaporins

Specialized channel proteins that facilitate the rapid transport of water across the cell membrane.

Active Transport

The energy-requiring movement of molecules against their concentration gradient (from low to high concentration), typically involving ATP and specific membrane transport proteins.

Membrane Potential

The voltage or electrical potential difference across a cell membrane that acts like a battery to influence the movement of charged substances.

Resting Potential

The electrical potential across the membrane of an unstimulated cell, typically around $-70\,\text{mV}$ in many cells.

Electrochemical Gradient

The combined concentration gradient and electrical voltage difference that drives the diffusion of ions across a cell membrane.

Gated Ion Channels

Membrane ion channels that open or close in response to specific stimuli, altering the membrane potential by permitting ion flow.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

An active transport pump that consumes ATP to set resting membrane potential by pumping three $\text{Na}^+$ ions out of the cell for every two $\text{K}^+$ ions pumped inside.

Electrogenic Pumps

Transport proteins that generate voltage across the membrane, such as the sodium-potassium pump and the proton pump.

Proton Pump

An electrogenic transport protein that actively pumps hydrogen ions ($\text{H}^+$) out of the cell.

Cotransport

A transport process in which the energy stored in the concentration gradient of one substance (such as $\text{H}^+$) is used to drive the transport of another substance (such as sucrose) against its own concentration gradient.

Osmosis

The passive transport of water across a selectively permeable membrane from an area of higher free water concentration (lower solute concentration) to an area of lower free water concentration (higher solute concentration).

Tonicity

The ability of an extracellular solution to cause a cell to gain or lose water, determined primarily by the relative concentration of nonpenetrating solutes.

Isotonic Environment

A solution condition in which the solute concentration is equal inside and outside the cell, resulting in balanced water exchange and cell stability.

Hypertonic Environment

An environment where the external solute concentration is higher than inside the cell, causing net water loss that can result in cell shrinkage or crenation.

Hypotonic Environment

An environment where the external solute concentration is lower than inside the cell, causing water to enter the cell and leading animal cells to swell or burst.

Turgid

The firm, healthy structural state of a plant cell resulting from water uptake when placed in a hypotonic solution.

Flaccid

The limp physical state of a plant cell that occurs when water is lost from the cell.

Plasmolysed

The state of a plant cell in which the plasma membrane pulls away from the cell wall due to severe water loss, causing the plant to wilt.

Water Potential

A physical property incorporating solute concentration and physical pressure that predicts the direction of water flow from regions of higher potential to lower potential.

Solute Potential ($\Psi_s$)

A component of water potential that is always zero or negative, calculated using $\Psi_s = -iCRT$, where pure water has a value of $0$.

Exocytosis

A bulk transport mechanism where intracellular vesicles fuse with the plasma membrane to secrete materials outside the cell.

Endocytosis

The process of taking large quantities of materials into the cell by engulfing them in inward-budding membrane vesicles.

Prokaryotic Cells

Cells lacking membrane-bound organelles that existed on Earth for approximately $1\text{ billion}$ years before the appearance of eukaryotic cells.

Eukaryotic Cells

Cells defined by the presence of a nucleus and membrane-bound organelles that divide the internal space into discrete functional compartments.

Compartmentalization

The division of cellular space into distinct organelle environments by internal membranes, optimizing enzymatic reactions and preventing interfering chemical processes.

Endosymbiont Theory

The theory stating that mitochondria and chloroplasts originated when an ancestral eukaryotic cell engulfed an oxygen-using, non-photosynthetic prokaryotic cell that became an integrated organelle.