1. When we go deep into the sea, the oxygen level decreases. Oxygen is in dissolved state in water.
2. Humans are adapted for utilizing oxygen in gaseous state. They cannot use dissolved oxygen for breathing.
3. Only aquatic animals like fish can utilize the dissolved oxygen for breathing using gills.
4. Human beings have lungs for respiration. Therefore, sea divers have to carry oxygen cylinders in their back so as to receive oxygen.
5. If they do not carry them, they do not get oxygen and there is a chance even to die.
