AP Biology Unit 2: Cell Structure and Function - Passive Transport and Osmoregulation

Vocabulary flashcards covering core transport mechanisms, osmosis, solution tonicity, water potential, and osmoregulation from the AP Biology Unit 2 study guide.

Passive Transport

The movement of substances across a cell membrane down their concentration gradient without the expenditure of cellular energy.

Simple Diffusion

The passive movement of small, nonpolar molecules (such as $CO_2$, $O_2$, and $N_2$) directly through the phospholipid bilayer from an area of higher concentration to lower concentration.

Facilitated Diffusion

A type of passive transport that moves molecules down their concentration gradient across the membrane using specific transmembrane proteins, such as ion channels and carrier proteins.

Ion Channels

Transmembrane proteins that provide specialized pores or passages allowing specific charged ions to move across the cell membrane during facilitated diffusion.

Carrier Proteins

Membrane proteins that bind specific solute molecules and alter their shape to shuttle the solute across the cell membrane during facilitated diffusion.

Osmosis

The net diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

Salinity

The dissolved salt content of a solution, which influences osmotic balance and the movement of water across membranes.

Osmotic Concentration

The total concentration of all solute particles in a solution, determining its tendency to take in water by osmosis.

Molarity

A standard unit of solute concentration used in cell concentration graphs (typically plotted on the x-axis) to assess changes in cell mass.

Osmoregulation

The active cellular and physiological control of internal solute concentrations and water balance within an organism.

Hypotonic Solution

A solution that has a lower solute concentration than the cytoplasm of a cell, causing water to move into animal cells (often causing lysis) and plant cells (maintaining turgor).

Hypertonic Solution

A solution that has a higher solute concentration than the cytoplasm of a cell, causing net water movement out of the cell, leading to shriveling in animal cells and plasmolysis in plant cells.

Isotonic Solution

A solution whose solute concentration is equal to that of the cell interior, resulting in dynamic equilibrium with no net movement of water.

Contractile Vacuole

A specialized organelle found in freshwater protists that accumulates and periodically expels excess water to prevent cell swelling and lysis in hypotonic environments.

Water Potential

The physical property that predicts the direction of water movement; water always flows spontaneously from regions of higher (more positive/less negative) water potential to regions of lower (more negative) water potential.

Transpiration

The process by which water is transported through a plant and evaporates from aerial parts such as leaves, governed by gradients in water potential between the soil, plant tissues, and the atmosphere.