Photic Zone: Which layer is sunlit for photosynthesis?

Photic Zone: Which layer is sunlit for photosynthesis?

• A. Photic zone
• B. Thermocline
• C. Aphotic zone
• D. Benthic zone

Answer: (A)

Light that can drive photosynthesis is confined to the upper part of the ocean where sunlight penetrates the water. This sunlit region is the photic zone, where phytoplankton and some algae use light to convert CO2 into organic matter. Deeper down, light fades quickly and photosynthesis becomes negligible, which defines the aphotic zone. The thermocline isn’t a light boundary—it’s a layer where temperature changes rapidly with depth. The benthic zone refers to the ocean bottom; it can be sunlit in very shallow areas, but in most of the water column the bottom is dark. So the layer where photosynthesis can occur due to light is the photic zone.

Light that can drive photosynthesis is confined to the upper part of the ocean where sunlight penetrates the water. This sunlit region is the photic zone, where phytoplankton and some algae use light to convert CO2 into organic matter. Deeper down, light fades quickly and photosynthesis becomes negligible, which defines the aphotic zone. The thermocline isn’t a light boundary—it’s a layer where temperature changes rapidly with depth. The benthic zone refers to the ocean bottom; it can be sunlit in very shallow areas, but in most of the water column the bottom is dark. So the layer where photosynthesis can occur due to light is the photic zone.