Final answer:
Dissolved oxygen is important for aquatic life as organisms need it to survive. The acceptable level of dissolved oxygen for life depends on the species but is generally above 5 mg/L.
Step-by-step explanation:
Organisms that live in water need to obtain oxygen from the water. Oxygen dissolves in water but at a lower concentration than in the atmosphere. Fish and many other aquatic organisms have evolved gills to take up the dissolved oxygen from water. Gills are thin tissue filaments that are highly branched and folded, and they allow the rapid diffusion of oxygen from water into the bloodstream. The acceptable level of dissolved oxygen for aquatic life varies depending on the specific species, but generally, a level above 5 mg/L is considered suitable for most aquatic organisms.