Which of the following present challenges that make gas exchange more difficult for fish than for terrestrial animals?

Question

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Water is denser and more viscous than air, making it more difficult for fish to move it over their gills for gas exchange. Additionally, water contains much less oxygen than air per unit volume, so fish need to extract as much oxygen as possible from the water that passes over their gills. Finally, diffusion occurs more slowly in water than in air, further limiting the efficiency of gas exchange in fish. While gills do have less surface area than lungs, this alone does not make gas exchange more difficult for fish than for terrestrial animals. Unidirectional flow of water may be less efficient than tidal ventilation, but this does not factor into the basic challenge of gas exchange in water.

Which of the Following Present Challenges That Make Gas Exchange