AP Biology Unit 2 - Cellular Transport and Water Potential

Vocabulary practice flashcards covering cell transport mechanisms, tonicity, osmosis, and water potential calculations for AP Biology Unit 2.

Passive Transport

The movement of molecules across a cell membrane without requiring cellular energy ($\text{ATP}$), as molecules move along or down their concentration gradient.

Active Transport

The movement of molecules across a cell membrane against their concentration gradient, requiring energy input such as the hydrolysis of $\text{ATP}$.

Endocytosis

A cellular transport process in which substances are brought into the cell by engulfing them in a membrane-bound vesicle.

Exocytosis

A cellular transport process by which materials are expelled outside the cell through the fusion of a vesicle membrane with the plasma membrane.

Sodium-Potassium Pump

A membrane protein pump that uses energy from hydrolyzing $\text{ATP}$ to $\text{ADP} + \text{P}_i$ to actively transport $\text{Na}^+$ ions out of the cytoplasm and $\text{K}^+$ ions into the cell.

Aquaporin

A specialized channel protein in the cell membrane designed to facilitate the rapid transport of water molecules across the membrane.

Hypertonic Solution

A solution that has a higher solute concentration compared to the inside of a cell, causing a net flow of water out of the cell.

Hypotonic Solution

A solution that has a lower solute concentration compared to the inside of a cell, causing a net flow of water into the cell.

Isotonic Solution

A solution that has an equal solute concentration compared to the inside of a cell, resulting in no net movement of water.

Osmosis

The passive diffusion of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential.

Water Potential ($\Psi$)

The measure of the potential energy in water that determines the direction of water movement, calculated as $\text{water potential} = \text{pressure potential} + \text{solute potential}$ or $\bar{\boldsymbol{\nabla}} = \bar{\boldsymbol{\nabla}}_P + \bar{\boldsymbol{\nabla}}_S$; pure water has a water potential of $0\,\text{MPa}$.

Pressure Potential ($\Psi_P$)

The component of water potential that accounts for physical pressure exerted on a solution, which can be positive (such as turgor pressure) or negative.

Solute Potential ($\Psi_S$)

The component of water potential that is proportional to the concentration of dissolved solutes, calculated using the formula $\Psi_S = -iCRT$, and is always negative for a solution.

Pressure Constant ($R$)

The molar gas constant value used in calculating solute potential, equal to $0.0831\,\frac{\text{liter bar}}{\text{mole }^\circ\text{K}}$.

Ionization Constant ($i$)

The number of particles a solute molecule produces when dissolved in water (for example, $i = 2.0$ for $\text{NaCl}$).

Temperature in Kelvin ($T$)

The absolute temperature used in the solute potential equation, calculated by adding $273$ to the temperature in degrees Celsius ($273 + ^\circ\text{C}$).

Sucrose Molarity vs. Mass Change Relationship

In potato core osmolarity experiments, increasing the molarity of sucrose in a beaker from $0.0\,M$ to $1.0\,M$ changes the mass change percentage from positive ($+18.0\%$) to increasingly negative ($-24.0\%$).