3B. Passive transport

Passive Transport

The movement of molecules across a membrane without requiring energy (ATP), driven by a concentration gradient. Includes diffusion, osmosis, and facilitated diffusion.

Active Transport

The movement of molecules against their concentration gradient (low to high concentration) using energy (ATP) and membrane proteins. Example: Sodium-potassium pump.

Diffusion

The passive movement of molecules from an area of higher concentration to an area of lower concentration, driven by kinetic energy, until equilibrium is reached.

Facilitated Diffusion

A type of passive transport where molecules move down their concentration gradient through a membrane protein, without requiring energy. Example: Glucose transport.

Protein Channel

A transmembrane protein that forms a pore, allowing specific molecules or ions to move across the plasma membrane via facilitated diffusion.

Carrier Protein

A membrane protein that binds to a specific molecule and undergoes a conformational change to transport it across the plasma membrane. Used in facilitated diffusion and active transport.

Conformational Change

A structural change in a protein’s shape, allowing it to perform its function, such as carrier proteins transporting substances across a membrane.

Concentration Gradient

The difference in the concentration of a substance between two areas, driving passive and active transport across membranes.

Kinetic Energy

The energy of motion, responsible for the random movement of molecules that drives diffusion and osmosis.

Solute

A substance that dissolves in a solvent to form a solution. Example: Salt in water.

Solvent

The liquid in which a solute dissolves to form a solution. Example: Water in saltwater.

Solution

A homogeneous mixture of a solute dissolved in a solvent. Example: Saltwater.

Tonicity

The ability of a solution to affect a cell’s water movement due to differences in solute concentration. Includes hypertonic, isotonic, and hypotonic solutions.

Hypertonic

A solution with a higher solute concentration than the inside of the cell, causing water to move out of the cell by osmosis, leading to shrinking (crenation in animal cells, plasmolysis in plant cells).

Hypotonic

A solution with a lower solute concentration than the inside of the cell, causing water to move into the cell by osmosis, leading to swelling and possibly lysis in animal cells. Plant cells become turgid.

Isotonic

A solution where the solute concentration is equal inside and outside the cell, resulting in no net movement of water. The cell remains in equilibrium.

Osmosis

The passive movement of water molecules across a selectively permeable membrane, from an area of lower solute concentration to an area of higher solute concentration, until equilibrium is reached.

Haemolysis

The rupture of red blood cells due to excessive water intake in a hypotonic solution, causing them to swell and burst.

Lysis

The breaking or bursting of a cell membrane, often due to excessive water intake in a hypotonic solution. In red blood cells, this is called haemolysis.

Plasmolysis

The shrinking of the cytoplasm in a plant cell due to water loss in a hypertonic solution, causing the plasma membrane to pull away from the cell wall.

Turgid

A plant cell in a hypotonic solution, where water enters by osmosis, making the cell swollen and firm. The cell wall prevents bursting.

Flaccid

A plant cell in an isotonic solution, where no net water movement occurs. The cell becomes limp, leading to reduced structural support in plant tissues.

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