Summary
Highlights
Respiration is an exothermic reaction that continuously occurs in living cells, transferring energy from glucose by breaking down glucose molecules. Energy is not created but transferred from glucose.
Organisms use energy from respiration for various functions, including building larger molecules from smaller ones (e.g., proteins from amino acids), muscular contraction for movement, and maintaining body temperature.
Aerobic respiration occurs when there is enough oxygen and is the most efficient way to transfer energy from glucose. It happens continuously in plants and animals within mitochondria. The word equation is glucose + oxygen → carbon dioxide + water.
Anaerobic respiration occurs without oxygen, typically in strenuous situations like sprinting. In humans, the word equation is glucose → lactic acid. It's less efficient because glucose is only partially broken down, and it produces toxic lactic acid.
In plants and yeast, anaerobic respiration results in glucose → ethanol + carbon dioxide. This process is called fermentation in yeast and is used industrially to make bread fluffy (due to carbon dioxide) and to produce alcoholic beverages like beer and wine (due to ethanol).