Concept:In a sealed aquarium, light energy drives the oxygen–carbon dioxide cycle needed for survival.
Explanation:The aquarium is air-tight, so gases cannot enter or escape from the outside.
Plants inside require light energy to perform photosynthesis and produce
O2.
Animals then use this
O2 for respiration and release
CO2, which plants need.
Without sufficient light, photosynthesis stops,
O2 becomes depleted, and all organisms are threatened.
Therefore, light energy is the most important external factor for maintaining the ecosystem inside.
Answer:A. light energy
