The process in living organisms of taking in oxygen from the surroundings and giving out carbon dioxide is external respiration.
The chemical breakdown of complex organic substances, such as carbohydrates and fats, that takes place in the cells and tissues of animals and plants, during which energy is released and carbon dioxide produced is internal respiration.
The respiration which takes place in the presence of oxygen is called aerobic respiration.
The respiration which takes place in the absence of oxygen is called anaerobic respiration.