Describe the importance of primary producers in maintaining atmospheric oxygen levels.

• A. Photosynthetic producers release oxygen; large-scale photosynthesis maintains atmospheric O2; disruption can affect air quality
• B. Primary producers consume oxygen and release carbon dioxide
• C. They have no impact on oxygen levels
• D. They only affect water oxygen levels

Answer: (A)

Photosynthetic primary producers are the source of most of the oxygen in Earth’s atmosphere. Through photosynthesis, they use sunlight to convert carbon dioxide and water into sugars, releasing oxygen gas in the process. This ongoing production by plants on land and algae in the oceans keeps atmospheric O2 at levels that support aerobic (oxygen-using) life; if photosynthesis drops due to deforestation, climate stress, or pollution, the balance can shift and air quality related to oxygen availability can be affected. While respiration in animals and microbes consumes oxygen, primary producers replenish what is used, so disrupting their large-scale activity changes the overall oxygen in the atmosphere. The idea that producers only consume oxygen and release carbon dioxide, or that they have no impact or only affect water oxygen, doesn’t fit the dominant role of photosynthesis in maintaining atmospheric O2.