What Keeps a Drowning Man From Breathing the Oxygen in the Water?

The biological design of a fish and a human differ significantly, especially their respiratory systems. The respiratory system of a fish is specifically designed to absorb oxygen from water, while the human respiratory system is made to breathe oxygen from air.

  1. Human Respiratory System

    • The main organs of the human respiratory system are the lungs. Inside the lungs are tubes called bronchi. Bronchi branch into even smaller tubes that have tiny bubbles, or sacs, at the ends. These sacs are called alveoli. The alveoli are in charge of passing oxygen from the lungs into the bloodstream.

    Fish Respiratory System

    • Unlike humans, fish don't have lungs. They have gills, which help them obtain oxygen from water. These gills - located on the sides of the fish, just behind the mouth - are especially designed to extract oxygen from water. When a fish allows water to enter its body, the water passes through the gills and the gill rakers, which filter the water and provide oxygen to fish cells.

    Why Can't Humans Breathe Oxygen From Water?

    • The answer is simple: because humans don't have gills. Gills are what allow this extraction of oxygen from water. Marine mammals, such as whales and dolphins, don't have gills. Although they live in water, they don't use water's oxygen to breathe. Rather, they hold their breath for long periods of time, and eventually come up to the surface to take a new breath.