Biology CLEP Prep Practice Exam

What is the main source of energy on Earth?

1. Fossil fuels

2. Nuclear reactions

3. Photosynthesis

4. Wind power

The correct answer is: Photosynthesis

Photosynthesis is the process through which plants convert light energy from the sun into chemical energy, which is then used by other organisms as a source of food and ultimately becomes the main energy source for the planet. Fossil fuels, nuclear reactions, and wind power are all sources of energy that depend ultimately on the energy from the sun and are not the main source of energy on Earth. Fossil fuels are formed from decayed organic matter, nuclear reactions also rely on the decay of radioactive elements, and wind power is heavily influenced by the sun's energy patterns. Photosynthesis stands as the primary source of energy on Earth because it transforms light energy from the sun into a usable energy form for living organisms.