How Cells Use Energy



sequence of chemical reactions that constructs or synthesizes molecules from smaller units

ATP synthase

enzyme complex that generates ATP by phosphorylating ADP


organism that can make its own food


sequence of chemical reactions that breaks down or decomposes molecules into smaller units while generating energy

chemical potential energy

energy released during a chemical reaction

citric acid cycle

series of chemical reactions used by all aerobic organisms to release ATP

electron transport chain

series of electron transporters that move electrons from NADH and FADH2 to oxygen molecules. Protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.

endergonic reaction

reaction that takes in energy

enthalpy (H)

measure of the bond energy of a system

entropy (S)

measure of the disorder or predictability of a system


biological molecule that catalyzes a biological reaction


state in which there is no net change through time; state when changes will not occur

exergonic reaction

reaction that releases energy

free energy

capacity of a system to do work


metabolic pathway in which glucose is broken down into pyruvate in the cytoplasm of the cell


organism that obtains energy and carbon from consuming other organisms

kinetic energy

energy an object possesses when in motion


on a molecular level, the biological processes that build or break molecules; on an organismal level, all of the chemical reactions within an organism that provide cells with the capacity to acquire energy and use that energy to carry out different functions

oxidative phosphorylation

production of ATP through chemiosmosis in the mitochondria through an electron transport chain