The gas that plants primarily absorb during photosynthesis is carbon dioxide (CO2). This process occurs in the chloroplasts of plant cells, where light energy is harnessed by chlorophyll to convert carbon dioxide and water into glucose and oxygen. The absorbed carbon dioxide is taken from the atmosphere through small openings in the leaves called stomata. Photosynthesis is crucial for life on Earth, as it produces the oxygen we breathe and serves as the foundation for the food chain, with plants converting solar energy into chemical energy stored in carbohydrates. This biological process underscores the importance of plants in regulating atmospheric CO2 levels.