Final answer:
The growth of a fungus in an aquarium can disrupt the energy flow by blocking sunlight from reaching photosynthetic organisms, leading to a decrease in oxygen production and nutrient availability in the ecosystem.
Step-by-step explanation:
The growth of a fungus that covers the walls and sides of an aquarium can disrupt the energy flow in the ecosystem of the aquarium. The disruption occurs because the fungus competes with photosynthetic organisms, like algae, for resources such as sunlight and nutrients. As the fungus covers the walls of the aquarium, it blocks sunlight from reaching the photosynthetic organisms, preventing them from carrying out photosynthesis and producing energy. This can lead to a decrease in oxygen production and nutrient availability in the ecosystem, affecting the overall energy flow and the organisms that depend on it.