Final answer:
Air-breathers have an easier time getting rid of CO2 compared to water-breathers due to the difference in density between air and water.
Step-by-step explanation:
In general, air-breathers have an easier time getting rid of CO2 compared to water-breathers. This is because air, being less dense than water, allows for more efficient gas exchange. In air-breathers, CO2 can be expelled quickly and easily through breathing. On the other hand, water-breathers, such as fish, need to extract oxygen from the water and release CO2 into it, which requires more energy and effort.