How did cyanobacteria, oxygen, and ozone impact the evolution of eukaryotic cells?

Question

What will be an ideal response?

Answer 1

Answer: The first phototrophs on Earth were anoxygenic bacteria, meaning that oxygen was NOT produced during photosynthesis. Eventually the Cyanobacteria evolved and oxygenic photosynthesis began to produce oxygen-the first major source of oxygen on Earth. As the oxygen was produced, it first reacted with all of the reduced chemicals found on early Earth, but eventually it began to accumulate in the atmosphere. As the oxygen gas accumulated, UV light converted the oxygen into ozone. Ozone absorbs UV irradiation and the formation of the ozone layer protected the Earth's surface from strong UV irradiation. Because UV irradiation damages DNA and other biomolecules, before the ozone layer life could only exist in protected environments, such as deep in the ocean or in the subsurface. The production of oxygen by Cyanobacteria thus did two very important things that may have helped eukaryotic and multicellular organisms evolve. The oxygen was a powerful oxidant and excellent source of energy (excellent electron acceptor for respiration) and the large majority of eukaryotic cells use aerobic respiration to generate large amounts of energy for cellular growth. All of this energy may have fueled the growth and diversity of multicellular organisms. In addition, the protection of the ozone layer allowed life to expand into new environments.