Diffusion

The spontaneous movement of a substance down its concentration gradient from where it is more concentrated to where it is less concentrated

Passive transport

The diffusion of a substance across a biological membrane, with no expenditure of energy

Osmosis

The diffusion of water across a selectively permeable membrane

Facilitated diffusion

The passage of substance through a specific transport protein across a biological membrane down to its concentration gradient

Active transport

The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring an input of energy (often as ATP)

Concentration gradient

A region along which the density of a chemical substance increases or decreases. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, substances tend to move from where they are more concentrated to where they are less concentrated

Hypotonic

Referring to a solution that, when surrounding a cell, will cause the cell to take up water

Hypertonic

Referring to a solution that, when surrounding a cell, will cause the cell to lose water

Isotonic

Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell

Aquaporin

A transport protein in the plasma membrane of some plant or animal cells that facilitates the diffusion of water across the membrane (osmosis)

Exocytosis

The movement of materials out of the cytoplasm of a cell by the fusion of vesicles with the plasma membrane

Endocytosis

Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane

Phagocytosis

Cellular "eating"; a type of endocytosis in which a cell engulfs macromolecules, other cells, or particles into its cytoplasm

Pinocytosis

Cellular "drinking"; a type of endocytosis in which the cell takes fluid and dissolved solutes into small membraneous vesicles

Receptor-mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles, which contain proteins with receptor sites specific to the molecules being taken in

Enzyme

A macromolecule, usually a protein, that serves as a biological catalyst, changing the rate of a chemical reaction without being consumed bt the reaction

Substrate

(1)A specific substance (reactant) on which an enzyme acts. Each enzyme recognizes substrate or substrates of the reaction it catalyzes (2) A surface in or on which an organism

Active site

The part of an enzyme molecule where a substrate molecule attaches (by means of weak chemical bonds); typically, a pocket or groove on the enzyme's surface.

Induced fit

The change of shape of an active site of an enzyme, caused by the entry of the substrate, so that it binds more snugly to the substrate

Cofactor

A non protein molecule or ion that is required for the proper functioning of an enzyme

Coenzyme

An organic molecule serving as a cofactor. Most vitamins functions as a coenzymes in important metabolic reactions

Competitive inhibitor

A substance that reduces the activity of an enzyme by binding to the enzyme's active site in place of the substrate. A competitive inhibitor's structure mimics that of the enzyme's substrate.

Non-competivie inhibitor

A substance that reduces the activity of an enzyme without entering an active site. By binding elsewhere on the enzyme, a noncompetitive inhibitor changes the shape of the enzyme so that the active site no longer effectively catalyzes the conversion of substrate to product

Allosteric site

A site that allows molecules to either activate or inhibit (or turn off) enzyme activity

Kinetic energy

The energy of motion

Potential energy

The energy that matter possesses because of its location or arrangement.

Entropy

A measure of disorder

Exergonic

An energy-releasing chemical reaction in which the reactants contain more potential energy than the products.

Endogonic

An energy-requiring chemical reaction, which yields more potential energy in the products than the reactants.

Aerobic

A process that requires the presence of oxygen or air as opposed to an anaerobic process that does not require it

Anarobic

Any organism that does not require molecular oxygen for growth

1st Law of Thermodynamics

Energy can neither be created nor destroyed

2nd Law of Thermodynamics

For a spontaneous process, the entropy of the universe increases