Biology Regents Practice Exam

How are carbon dioxide and oxygen cycled in ecosystems?

1. They are stored in the tissues of animals.

2. They are recycled through the activity of living and nonliving systems.

3. They are lost due to the activities of decomposers.

4. They are only released through photosynthesis.

The correct answer is: They are recycled through the activity of living and nonliving systems.

In ecosystems, carbon dioxide and oxygen are integral components that are continually recycled through various processes involving both living organisms and nonliving systems. The cycling begins with photosynthesis, where plants utilize carbon dioxide and sunlight to produce glucose and oxygen. This oxygen is then released into the atmosphere. Animals, on the other hand, consume oxygen during cellular respiration to convert glucose into energy, releasing carbon dioxide as a byproduct, which is then available for plants to use again. This back-and-forth exchange exemplifies a cyclical relationship between carbon dioxide and oxygen, influenced by biotic factors like plants and animals, and abiotic factors like the atmosphere and soil. This cyclical nature highlights the importance of both living and nonliving systems in maintaining the balance of gases essential for life on Earth. The processes are interlinked: during respiration, carbon dioxide is released, while during photosynthesis, oxygen is produced, demonstrating the vital role both gases play in sustaining ecosystems.