Cell Membrane Transport, Osmosis, and Water Potential

Vocabulary practice flashcards covering cell membrane permeability, passive and active transport mechanisms, bulk transport, tonicity, and water potential equations.

Water Potential

A measure of the ability of water molecules to move freely in solution; more free water molecules result in a higher water potential, and water moves from an area with higher water potential (closer to $0$) to an area with lower water potential (more negative).

Solute Potential ($\Psi_s$)

A component of water potential calculated by the formula $\Psi_s = -iCRT$, representing the reduction of free water molecules due to their clustering around dissolved polar or ionic solutes.

Pressure Potential ($\Psi_p$)

The physical pressure exerted on a solution, which is equal to $0$ in an open container.

Water Potential Formula

$\Psi = Ψ_p + Ψ_s$, where $\Psi$ is total water potential, $\Psi_p$ is pressure potential, and $\Psi_s$ is solute potential.

Ionization Constant ($i$)

The number of particles a solute molecule forms when dissolved in water, which is $1$ for sucrose and $2$ for $\text{NaCl}$.

Channel Proteins

Transport proteins that span the membrane and have a hydrophilic channel allowing specific molecules or ions to pass through.

Aquaporin

A specific channel protein that allows water to move into and out of the cell.

Carrier Proteins

Transport proteins that span the membrane and change shape to allow a specific molecule into or out of the cell.

Diffusion

The movement of molecules from an area of high concentration to an area of lower concentration until equilibrium is reached.

Concentration Gradient

A region along which the concentration of a substance decreases, where one substance's gradient is not affected by the concentration gradient of other substances.

Passive Transport

The movement of materials across a biological membrane without the expenditure of cellular energy.

Osmosis

The passive diffusion of water across a membrane.

Tonicity

The ability of a solution to cause a cell to gain or lose water, based on the concentration of solutes in the solution that cannot move through the membrane.

Isotonic Solution

A solution that has the same concentration of non-penetrating solutes inside and outside the cell, resulting in no net movement of water.

Hypertonic Solution

A solution with a higher concentration of solutes outside the cell than inside, causing water to leave the cell and dehydrate it.

Hypotonic Solution

A solution with a lower concentration of solutes outside the cell than inside, causing water to enter the cell (which can cause cell lysis or bursting).

Osmoregulation

The control of solute concentration and water balance in an organism, such as the use of a contractile vacuole in Paramecium to excrete excess water in hypotonic environments.

Turgor Pressure

The opposing pressure that a plant cell wall exerts on the cell, preventing further water uptake when the cell is placed in a hypotonic solution.

Turgid

The normal, firm state of a plant cell when placed in a hypotonic solution, where the cell wall supports the cell and helps maintain the shape of the organism.

Flaccid

The limp condition of a plant cell and its cell wall when placed in an isotonic solution.

Plasmolysis

The phenomenon occurring in a plant cell placed in a hypertonic solution where water exits, causing the cell membrane to pull away from the cell wall and likely leading to wilting.

Facilitated Diffusion

The passive diffusion of molecules across the cell membrane facilitated by transport proteins.

Ion Channels

Transport proteins that facilitate the passage of ions; some are gated and require a stimulus such as an electrical charge or binding substance to open.

Active Transport

The movement of molecules against their concentration gradient requiring the expenditure of energy (usually $\text{ATP}$).

Ion Pumps

Carrier mechanisms that move ions across a biological membrane using active transport.

Membrane Potential

The voltage across a biological membrane caused by an uneven distribution of ions on opposite sides.

Electrochemical Gradient

The combined drive acting on an ion, composed of its chemical concentration gradient across the membrane and the electrical effect of membrane potential on its movement.

Electrogenic Pump

An ion transport pump that generates a voltage across a membrane by moving ions to establish an electrochemical gradient (e.g., proton pumps that move protons against their concentration gradient using $\text{ATP}$).

Cotransport

A mechanism in which a specialized transport protein couples the downhill movement of one molecule along its concentration gradient with the uphill movement of another molecule against its concentration gradient.

Bulk Transport

A form of active transport involving the movement of large molecules across the membrane using vesicles.

Exocytosis

A type of bulk transport in which vesicles fuse with the cell membrane to discharge their contents out of the cell into the extracellular fluid.

Endocytosis

A bulk transport process where the plasma membrane infolds to capture external substances and enclose them within newly formed vesicles.

Phagocytosis

A form of endocytosis in which a cell engulfs another cell or large particle to form a food vesicle, which later fuses with a lysosome for digestion.

Pinocytosis

A type of endocytosis involving the nonspecific uptake of extracellular fluid droplets, sometimes producing vesicles coated with a fuzzy protein layer.

Receptor-Mediated Endocytosis

A specialized form of endocytosis in which outer membrane receptor proteins bind specific target substances present at low concentrations before vesicle formation occurs.