Pre-engagement: Perhaps the most common meaning of a promise ring is the commitment to a relationship that is headed toward engagement. When you feel that your partner is the right one for you but you arenât quite ready for marriage, a promise ring is also known as a pre-engagement ring.
There is a big difference between external and internal respiration. External respiration is basically the transfer of gas between respiratory organs such as lungs and the outer environment. It takes place prior to internal respiration.Internal respiration is the transfer of gas between the blood and cells. External respiration also known as breathing refers to a process of inhaling oxygen from the air into the lungs and expelling carbon dioxide from the lungs to the air.Exchange of gases both in and out of the blood occurs simultaneously.here is a big difference between external and internal respiration. External respiration is basically the transfer of gas between respiratory organs such as lungs and the outer environment. It takes place prior to internal respiration.
(The processes of internal respiration concern the exchange of gases in the lungs with those in the tissues and is described on the next page). The processes of breathing or  respiration  are often described in two parts: External Respiration and Internal Respiration.