Exercise 2 solution

(a) 50 m: epipelagic (sunlight zone). Sunlight reaches it.
(b) 600 m: mesopelagic (twilight zone). Only faint light reaches it, too little for photosynthesis.
(c) 2,500 m: bathypelagic (midnight zone). No sunlight.
(d) 8,000 m: hadal zone, found only in the deepest trenches. No sunlight.

Boundaries vary slightly between textbooks, so a depth close to an edge may be placed differently.