IB Marine Science Standard Level (SL) Practice Exam

Light penetration with depth defines ocean zones. The sunlit layer where enough light reaches for photosynthesis is the photic zone. Beneath that, the aphotic zone receives little to no light, so photosynthesis can’t occur and most organisms rely on organic matter produced in upper layers or other energy sources. Sediments like silt and siliceous ooze are not depth zones; they describe deposits on the seafloor, not light levels.