Why was the evolution of photosynthesizing bacteria important to most modern organisms?

• A. They directly provided glucose to all multicellular organisms.
• B. They released oxygen into the atmosphere, enabling aerobic respiration.
• C. They increased the amount of carbon dioxide in the atmosphere.
• D. They caused the extinction of all anaerobic organisms.

Answer: (B)

Verified step by step guidance

1. Understand the role of photosynthesizing bacteria in Earth's history: Photosynthesizing bacteria, such as cyanobacteria, were among the first organisms to perform photosynthesis, a process that converts light energy into chemical energy while releasing oxygen as a byproduct.
2. Recognize the significance of oxygen release: Photosynthesizing bacteria released oxygen into the atmosphere, which was previously low in oxygen. This process, known as the Great Oxygenation Event, transformed Earth's atmosphere and made it suitable for aerobic organisms.
3. Connect oxygen release to aerobic respiration: Aerobic respiration is a process used by most modern organisms to efficiently produce energy (ATP) using oxygen. The oxygen released by photosynthesizing bacteria enabled the evolution of aerobic organisms, which rely on oxygen for survival.
4. Clarify why glucose is not directly provided: Photosynthesizing bacteria produce glucose for their own use during photosynthesis, but they do not directly provide glucose to multicellular organisms. Instead, they contribute to the ecosystem by producing oxygen and serving as a food source for other organisms.
5. Address the extinction of anaerobic organisms: While the increase in atmospheric oxygen caused some anaerobic organisms to decline, many anaerobic organisms adapted to survive in low-oxygen environments. Photosynthesizing bacteria did not cause the extinction of all anaerobic organisms.