The primary gas that plants absorb during photosynthesis is carbon dioxide (CO2). This process occurs in the chloroplasts of plant cells, where light energy is converted into chemical energy. During photosynthesis, plants take in carbon dioxide from the air through small openings called stomata. Using sunlight and water, they convert the carbon dioxide into glucose, a sugar that serves as energy for growth and development. Oxygen is released as a byproduct of this process, which is essential for the respiration of most living organisms. Therefore, carbon dioxide plays a vital role in the plant life cycle and the earth's ecosystem.