AP Biology: Cell Transport, Facilitated Diffusion, and Osmoregulation

Vocabulary flashcards covering Topics 2.5, 2.6, and 2.7 of AP Biology Unit 2, including passive and active transport mechanisms, facilitated diffusion, and osmoregulation concepts.

Selective Permeability

The ability of cell membranes to act as selective barriers, allowing the formation of solute concentration gradients across the membrane to maintain internal homeostasis.

Passive Transport

The net movement of molecules from regions of high concentration to low concentration across a membrane without the direct input of metabolic energy ($\text{ATP}$).

Simple Diffusion

The passive movement of small, nonpolar molecules, such as oxygen ($\text{O}_2$) and carbon dioxide ($\text{CO}_2$), down their concentration gradient directly through the lipid bilayer.

Facilitated Diffusion

A passive transport process where polar or charged molecules move down their concentration gradient across the membrane with the assistance of specialized transport proteins.

Active Transport

The transport mechanism requiring direct input of metabolic energy ($\text{ATP}$) to move molecules against their concentration gradient (from low to high concentration).

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

An active transport protein that uses $\text{ATP}$ to pump $3$\ sodium ions ($\text{Na}^+$) out of the cell and $2$\ potassium ions ($\text{K}^+$) into the cell, creating an electrochemical gradient.

Endocytosis

A cellular process where the cell takes in large molecules or materials by folding the plasma membrane inward to form new vesicles.

Phagocytosis

A specific form of endocytosis commonly referred to as 'cell eating,' in which the cell engulfs solid particulate matter.

Pinocytosis

A specific form of endocytosis commonly referred to as 'cell drinking,' in which the cell takes in extracellular fluids and solutes.

Exocytosis

A bulk transport process where internal vesicles fuse with the plasma membrane to release materials out of the cell.

Fluid Mosaic Model

A model describing the membrane as a dynamic structure composed of proteins, cholesterol, and carbohydrates drifting in a fluid phospholipid bilayer.

Channel Proteins

Transport proteins that provide hydrophilic tunnels across the membrane for specific molecules or ions, often opening only in response to a stimulus.

Carrier Proteins

Transport proteins that undergo a conformational shape change to shuttle a specific bound molecule across the cell membrane.

Membrane Potential

An electrical gradient or voltage across a membrane created by the unequal distribution and movement of ions.

GLUT Transporters

Specific carrier proteins required to facilitate the entry of large polar glucose molecules across cell membranes.

Aquaporins

Specialized channel proteins that facilitate the rapid transport of large quantities of water molecules across biological membranes.

Saturation (V-max)

The condition in facilitated diffusion where the rate of transport reaches its maximum because all available transport protein binding sites are occupied.

CFTR Channel Protein

A transport protein that, when mutated in Cystic Fibrosis, fails to move chloride ions ($\text{Cl}^-$) out of cells, leading to osmotic disruption and thick mucus accumulation.

Antidiuretic Hormone (ADH)

A hormone that signals kidney cells to insert additional aquaporins into their membranes to reclaim water; failure in ADH signaling leads to Diabetes Insipidus.

Isotonic Environment

An environment where the solute concentration is equal inside and outside the cell, resulting in no net movement of water.

Hypertonic Environment

An environment with a higher solute concentration compared to the cell's interior, causing net movement of water out of the cell.

Hypotonic Environment

An environment with a lower solute concentration compared to the cell's interior, causing net movement of water into the cell.

Plasmolysis

The process in plant cells placed in a hypertonic environment where the cytoplasm shrivels and the plasma membrane pulls away from the cell wall.

Crenation

The shriveling of an animal cell when exposed to a hypertonic environment.

Lysis

The bursting of an animal cell due to excessive water intake when placed in a hypotonic environment.

Turgor Pressure

The outward physical pressure exerted against the plant cell wall by water stored inside the large central vacuole.

Water Potential ($\Psi$)

A measurement of the tendency of water to move from one area to another, where pure water has a potential of $0$, and water flows from high to low water potential.

Total Water Potential Equation

The formula $\Psi = \Psi_p + \Psi_s$, where total water potential ($\Psi$) is the sum of pressure potential ($\Psi_p$) and solute potential ($\Psi_s$).

Solute Potential Formula

The equation $\Psi_s = -iCRT$, used to calculate the effect of solute concentration on water potential.

Ionization Constant ($i$)

The factor in the solute potential formula representing the number of particles a solute forms in solution (e.g., $1.0$ for sucrose, $2.0$ for $\text{NaCl}$).

Pressure Constant ($R$)

The constant value used in calculating solute potential, equal to $0.0831\,\frac{\text{L}\cdot\text{bars}}{\text{mol}\cdot\text{K}}$.

Contractile Vacuole

A specialized organelle in freshwater protists like Paramecium that collects excess water and pumps it out of the cell to prevent lysis.

Osmoregulation

The process by which organisms regulate their internal water balance and solute concentrations to maintain dynamic homeostasis.