Lab 8: Diffusion and Osmosis

Passive Transport

The movement of substances across a biological membrane without the expenditure of cellular energy (ATP).

Active Transport

The movement of substances across a biological membrane against a concentration gradient, requiring cellular energy (ATP).

Concentration Gradient

A gradual difference in the concentration of a solute in a solution between two regions.

Simple Diffusion

The passive movement of solute particles from an area of higher concentration to lower concentration until equilibrium is reached.

Facilitated Diffusion

The passive transport of molecules across a membrane with the assistance of transport proteins (channels or carriers).

Osmosis

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

Primary Active Transport

Direct use of ATP energy to transport molecules across a cell membrane against their concentration gradient (e.g., Sodium-Potassium Pump).

Secondary Active Transport

Movement of a molecule against its gradient coupled to the downhill movement of another molecule, using energy from electrochemical gradients.

Sodium-Potassium Pump

An active transport protein that uses ATP to pump 3 Na+ ions out of a cell and 2 K+ ions into a cell.

Endocytosis

An active transport process where a cell engulfs external material into vesicles formed from the plasma membrane.

Exocytosis

An active transport process where vesicles fuse with the plasma membrane to release contents outside the cell.

Phagocytosis

A type of endocytosis where a cell engulfs large solid particles or whole cells ("cell eating").

Pinocytosis

A type of endocytosis where a cell takes in extracellular fluid and dissolved solutes ("cell drinking").

Receptor-Mediated Endocytosis

Specific endocytosis triggered when extracellular ligands bind to specific cell-surface receptors.

Equilibrium

A state in which solute concentration is uniform throughout a space and net movement of molecules ceases.

Solution

A homogeneous mixture composed of two or more substances (solute dissolved in a solvent).

Solvent

The substance in a solution that dissolves the solute (typically present in the largest amount, like water).

Solute

The substance that is dissolved in a solvent to form a solution.

Hypertonic Solution

A solution with a higher concentration of solutes compared to the inside of a cell.

Hypotonic Solution

A solution with a lower concentration of solutes compared to the inside of a cell.

Isotonic Solution

A solution with an equal concentration of solutes compared to the inside of a cell.

Cytolysis

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

Plasmolysis

The shrinkage of the cytoplasm away from the cell wall in a plant cell placed in a hypertonic solution.

Turgor Pressure

The pressure exerted by fluid pushing the cell membrane against the plant cell wall when in a hypotonic environment.

Crenation

The shrinking and spiky appearance of animal red blood cells when placed in a hypertonic solution.