Kaplan Nursing Entrance Practice Exam

What type of organisms are believed to be the first on Earth?

1. Autotrophs

2. Heterotrophs

3. Phototrophs

4. Decomposers

The correct answer is: Heterotrophs

The belief about the first organisms on Earth is primarily centered around the characteristics of heterotrophs. These are organisms that cannot produce their own food and instead rely on consuming organic materials created by other organisms. Early Earth is thought to have contained a variety of organic compounds that could have supported the survival of simple heterotrophic organisms, such as bacteria. These organisms would have relied on the existing organic matter in their environment for sustenance, which aligns well with what we know about the evolutionary timeline. In contrast, autotrophs, which produce their own food typically through photosynthesis or chemosynthesis, emerged later in Earth's history after heterotrophs. Phototrophs, a subset of autotrophs, specifically utilize light energy to synthesize food. Decomposers play a crucial role in breaking down dead organic material, recycling nutrients in ecosystems, but they too came after the first life forms that fed on naturally occurring organic compounds. Therefore, the characteristics of early forms of life are best captured by heterotrophs, making them the likely candidates for the first organisms on our planet.