What is a Promise Ring. A promise ring, sometimes known as a pre-engagement ring, is a simple piece of jewelry that is given as a symbol of a committed, monogamous relationship. In some cases, the promise ring symbolizes purity and a decision to remain celibate until marriage.
Noun. 1. external respiration-the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation. breathing, respiration, ventilation. artificial respiration-an emergency procedure whereby breathing is maintained artificially.
Anaerobic respiration is respiration that uses electron acceptors  other than oxygen. Anaerobic respiration can be found in protozoans  and bacteria. Anaerobic respiration is a type of cellular respiration. It occurs  when oxygen is not available or is available in very low  quantities. It is also a respiration in the absence of oxygen. Oxygen is not used as the final electron acceptor.