The gas that plants absorb for photosynthesis is carbon dioxide (CO2). Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose. This process occurs mainly in the chloroplasts of plant cells, where carbon dioxide from the air enters through tiny openings called stomata. When combined with water and sunlight, carbon dioxide is transformed into glucose and oxygen, the latter being released back into the atmosphere. This process is essential for life on Earth as it contributes to the oxygen we breathe.