Passive Transport and Cell Membrane Processes in Biology Save Groups

Passive Transport

The movement of molecules across the cell membrane WITHOUT the need of energy, or ATP; examples include diffusion, facilitated diffusion, and osmosis.

Concentration

The amount of solutes per unit volume of a solution; for example, in a sugar solution, it is the number of sugar molecules in a certain volume of water.

Concentration Gradient

The difference in concentration between two points in space or across a cell membrane. When molecules move from high concentration to low concentration, we say they are moving DOWN the concentration gradient. When molecules move from low concentration to high concentration, we say they are moving UP the concentration gradient.

Diffusion (or Simple Diffusion)

The movement of solute molecules from an area of high concentration (many molecules) to an area of low concentration (few molecules); this does not require energy because high/many to low/few movement of molecules is the natural flow - how the molecules want to move.

Facilitated Diffusion

The movement of solutes across the cell membrane from an area of high concentration (many solutes) to an area of low concentration (few solutes) with the help of a protein molecule embedded in the cell membrane; this does not require energy because high solute to low solute movement is the natural flow of molecules (this is how they WANT to move).

Homeostasis

The maintenance of a stable internal environment either in a single cell or in a multicellular organism.

Hypertonic

A solution that is more concentrated (more solute molecules) relative to another solution; in biology this will always refer to a solution OUTSIDE the cell that has a higher solute concentration.

Hypotonic

A solution that is less concentrated (fewer solute molecules) relative to another solution; in biology this will always refer to a solution OUTSIDE the cell that has a lower solute concentration.

Isotonic

Two solutions that have the same number of solute molecules, or the same solute concentration.

Osmosis

The movement of water from an area of low solute concentration to an area of high solute concentration; does not require energy. You can also think of it as the movement of water from high water potential (or where there is more water relative to solute) to low water potential (or where there is less water relative to solute).

Plasmolysis

The loss of water from a plant cell (specifically from the central vacuole of the plant cell) leading to the collapse of the cell membrane as it pulls away from the cell wall.

Lysis

The breakdown or disintegration of a cell due to the rupture of the cell membrane. This occurs when animal cells are placed in a hypotonic solution and the water flows into the cell.

Solute

In a solution, this is the molecule; for example in sugar water, the solute is the sugar molecule.