1. Gas Exchange: Both humans and fish need to take in oxygen (O2) and release carbon dioxide (CO2) to survive. This process of gas exchange happens across a thin, moist membrane.
2. Diffusion: The movement of oxygen and carbon dioxide across this membrane is driven by diffusion, meaning they move from areas of high concentration to areas of low concentration.
3. Respiratory Pigments: Both humans and fish use respiratory pigments to bind and transport oxygen throughout their bodies. Humans use hemoglobin, while fish use hemoglobin and sometimes hemocyanin (depending on the species).
Beyond these similarities, their systems differ significantly:
Humans:
* Lungs: Humans use lungs, which are internal air sacs, for gas exchange.
* Air Breathing: Humans breathe air and take it into their lungs through their nose and mouth.
* Active Transport: Humans use active transport (muscles and diaphragm) to move air in and out of their lungs.
Fish:
* Gills: Fish use gills, which are external, highly vascularized structures, for gas exchange.
* Water Breathing: Fish breathe dissolved oxygen from water that passes over their gills.
* Passive Transport: Fish rely on the flow of water over their gills for gas exchange, which is largely passive.
In Summary: While the fundamental need for oxygen and the basic mechanisms of gas exchange are similar, the structures and methods of breathing are completely different in humans and fish, reflecting their different environments and adaptations.