Final answer:
Living organisms release carbon dioxide through respiration, while photosynthesis removes carbon dioxide from the atmosphere. Burning organic material and geological processes also add carbon dioxide to the air.
Step-by-step explanation:
Carbon dioxide is added to the air through various processes. Living organisms release carbon dioxide as a byproduct of cellular respiration, while photosynthesis removes carbon dioxide from the atmosphere. Additionally, burning organic material, such as fossil fuels, releases carbon dioxide into the air. Volcanic eruptions and the heating of limestone during cement production also contribute to the release of carbon dioxide.