Breathing is when a gill converts from oxygen in water into oxygen in blood, and many people confuse breathing with respiration, but breathing is just the first step of respiration. Given these facts, what is it when a gill converts from oxygen in water into oxygen in blood among the following options:
- fertilization occurs
 - prolactin release
 - preventing heat transfer
 - first step of respiration
 - last step of digestion
 - flow of electrons
 - death
 - fish


 

    first step of respiration     