The process by which plants release oxygen is called photosynthesis. During photosynthesis, plants absorb carbon dioxide from the atmosphere and water from the soil, using sunlight as an energy source. This process takes place primarily in the chloroplasts of plant cells, where chlorophyll captures sunlight. The energy from sunlight converts carbon dioxide and water into glucose, a form of sugar that serves as energy for the plant, and oxygen, which is released as a byproduct. This process is vital for life on Earth, as it replenishes the atmosphere's oxygen supply and is fundamental to the food chain.