What is the ultimate source of energy for most ecosystems?

What is the ultimate source of energy for most ecosystems?

• A. Water
• B. Sun
• C. Geothermal energy from Earth's core
• D. Moonlight

Answer: (B)

Sunlight powers photosynthesis, the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in sugars. That chemical energy becomes the fuel for almost every other organism as it moves through food webs—herbivores eat producers, carnivores eat herbivores, and decomposers recycle nutrients. Water is essential for life and for the chemistry of the reactions, but it doesn’t supply energy on its own. Deep-sea hydrothermal-vent communities run on chemical energy from Earth’s interior, but these are rare compared with sun-powered systems. Moonlight is just reflected sunlight and provides negligible energy for metabolic processes. So, sunlight is the starting energy source for the vast majority of ecosystems.