Which zone is the twilight layer of the ocean where there is some light but not enough for photosynthesis?

• A. Aphotic Zone
• B. Photic Zone
• C. Disphotic Zone
• D. Biomass

Answer: (C)

Light fades quickly with depth, creating distinct ocean layers based on how much light is available. The surface layer receives enough light for photosynthesis, supporting phytoplankton. A step below, there’s a zone that still has some light reaching it but not enough to drive photosynthesis reliably—this is the twilight zone, the disphotic zone. That limited light means photosynthesis can’t sustain most plants there, so organisms adapt to low-light conditions and often rely on other energy sources or bioluminescence. Deeper still is the aphotic zone, where little to no light penetrates. Biomass isn’t a depth region, so it doesn’t describe a zone.