Membrane Transport Vocabulary

A set of 50 vocabulary flashcards covering membrane transport, permeability, diffusion rates, osmosis, and transport protein mechanisms based on lecture notes.

Phospholipid Bilayer

The basic planar, two-layer structure of a membrane composed of hydrophilic heads facing outward and hydrophobic tails facing inward.

Hydrophilic Head

The water-attracting, polar portion of a membrane phospholipid molecule.

Hydrophobic Tail

The water-repelling, nonpolar portion of a membrane phospholipid molecule.

Selectively Permeable Membrane

A membrane structure that allows small uncharged molecules to cross easily, while ions and large molecules cross very slowly or not at all.

Relative Membrane Permeability Hierarchy

The relative ease with which solutes cross a membrane, ordered as: small nonpolar molecules $\rightarrow$ small uncharged polar molecules $\rightarrow$ large uncharged polar molecules $\rightarrow$ small ions.

Membrane Fluidity

A physical state of the lipid bilayer that increases as temperature increases, leading to an increase in membrane permeability.

Diffusion

A type of passive transport characterized by the spontaneous, random movement of molecules and ions in all directions without energy input.

Solute Concentration Gradient

A state that exists when there is a difference in solute concentrations across space.

Net Solute Movement

The overall directional shift of solutes away from regions of high concentration, occurring even though individual solutes move randomly and spontaneously.

Electrochemical Gradient

The combined force of an electrical charge gradient (net positive and negative charges across a membrane) and a solute concentration gradient influencing ion movement.

Cellular Equilibrium

A state in which solute molecules are randomly distributed equally throughout a solution, resulting in equal movement in both directions and no net movement.

Diffusion Rate Formula

The mathematical expression $F = k A \frac{\Delta c}{d}$ used to calculate the rate at which solutes move across a membrane.

Diffusion Variable $F$

The variable in the diffusion equation representing the overall rate of diffusion.

Diffusion Constant $k$

A constant in the diffusion rate equation that depends on the specific solute, membrane properties, and temperature.

Surface Area Variable $A$

The variable in the diffusion rate equation representing the total membrane surface area available for diffusion.

Concentration Difference $\Delta c$

The variable in the diffusion rate equation representing the change in solute concentration across space.

Diffusion Distance $d$

The variable in the diffusion rate equation representing the distance across which solutes must diffuse.

Surface Area to Volume Ratio ($SA/V$)

A ratio that decreases as cell size increases, causing the diffusion distance to increase and the overall rate of diffusion to lower.

Plant Vacuole Function

An organelle strategy that reduces the internal volume of the protoplast, helping overcome the problem of a decreased surface area to volume ratio in larger plant cells.

Surface Complexity Adaptations

Cellular structures such as hairs or microvilli that increase total surface area to enhance diffusion rates.

Elongated and Flattened Cell Shapes

Morphological adaptations (such as thin tubes or flat cells) that keep diffusion distances small to maintain efficient transport rates.

Osmosis

The diffusion of water across a semi-permeable membrane that allows water to pass but restricts some or all solute molecules.

Bound Water

Water molecules tied to solute molecules by hydrogen bonds, preventing them from crossing a semi-permeable membrane when the solute cannot cross.

Free Water

Unbound water molecules involved in osmosis that move from regions of low solute concentration (high free water concentration) to regions of high solute concentration (low free water concentration).

Hypertonic Solution

A solution having a higher solute concentration relative to another solution.

Hypotonic Solution

A solution categorized relative to another solution based on solute concentration comparison.

Isotonic Solution

A solution having the same solute concentration relative to another solution.

Water Cohesion

The property of water molecules sticking to other water molecules due to hydrogen bonding.

Water Adhesion

The property of water molecules sticking to xylem walls due to hydrogen bonding.

Passive Transport

The movement of substances across a plasma membrane along an electrochemical gradient without requiring an outside energy source.

Active Transport

The directed movement of substances across a plasma membrane against an electrochemical gradient using an outside energy source and pumps.

Facilitated Diffusion

Passive transport of hydrophilic, polar, and charged solutes across a membrane using channel or carrier proteins.

Channel Proteins

Selective membrane proteins that form pores allowing specific ions or molecules to pass through the membrane.

Carrier Proteins

Membrane proteins that undergo a conformational change (change in shape) to move a specific molecule across the membrane.

Aquaporins

Selective channel proteins that allow water molecules to move across membranes while excluding other molecules and ions.

Gated Channels

Channel proteins that open or close in response to a specific signal.

Conformational Change

A change in shape experienced by a carrier protein when carrying a molecule across a membrane.

Membrane Pump

A membrane protein that carries out active transport using $ATP$ to move protons ($H^+$) or ions across membranes, affecting $pH$ and establishing gradients.

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

An active transport membrane pump that uses $ATP$ to move $Na^+$ and $K^+$ against their concentration gradients.

Sodium Binding in $Na^+/K^+$ Pump

The step where $3\,Na^+$ bind to the unbound pump protein, causing a conformational change that closes the entrance and opens an exit on the other side of the wall to release $Na^+$.

Potassium Binding in $Na^+/K^+$ Pump

The step where $2\,K^+$ bind to the unbound pump protein, causing a conformational change that closes the entrance and opens an exit inside the cell to release $K^+$.

Secondary Active Transport

A transport mechanism that couples the down-gradient movement of one solute with the against-gradient movement of another solute, using an electrochemical gradient established by primary active transport.

Cotransporters

Membrane proteins (such as symporters and antiporters) involved in secondary active transport that move two solutes simultaneously.

Symporter

A cotransporter that transports a solute against its concentration gradient using energy released by another molecule moving in the same direction down its concentration gradient.

Antiporter

A cotransporter that transports a solute against its concentration gradient using energy released by another molecule moving in the opposite direction down its concentration gradient.

Temperature Effect on Membranes

An environmental factor that increases membrane fluidity and affects the diffusion constant $k$.

Xylem Water Transport

The movement of water through plant vascular tissue driven by properties like cohesion between water molecules and adhesion to xylem walls.

Protoplast

The living cellular content of a plant cell whose effective internal volume is reduced by the vacuole to enhance diffusion efficiency.

Proton Pump ($H^+$ Movement)

A active transport pump that consumes $ATP$ to move protons ($H^+$) across a membrane to build electrochemical gradients and adjust $pH$.

$ATP$ Usage in Active Transport

The outside energy source utilized by membrane pumps to transport ions or molecules against their concentration or electrochemical gradients.