Food energy is a chemical energy used by humans through the process of cellular respiration. Food contain macromolecules such as lipids, proteins, carbohydrates, water, vitamins, and minerals that are necessary for the human metabolism and they are broken down and used by the series of metabolic steps (glycolysis, Krebs cycle, electront transport chain and oxidative phosphorilation). Digested macromolecules should be used either as a source of energy or as building blocks for the cell.
At the end of catabolic processes within an organism food energy is transformed into energy usable by the cell-ATP.
Wood is a flammable substance. Depending how dry it is will determine its flammability or what temperature it will burst into flame. Burning wood undergoes chemical property changes: the brown hard wood becomes a black pile of ashes.
