Question

Deep sea divers carry oxygen cylinders with them why?

Answer 1

Human Beings are adapted for terrestrial habitat and hence their respiratory system can utilize oxygen in gaseous state, in aquatic habitat, organisms utilize oxygen which is in dissolved state in water.
as humans cannot utilize dissolved oxygen deep sea divers have to carry oxygen cylinders.

Answer 2

Deep sea diver carry oxygen cylinder on their back as the depth of sea increase level of oxygen get decrease. just to provide oxygen to the body sea rivers carry oxygen.