The primary function of chloroplasts in plant cells is to facilitate photosynthesis, a process through which plants convert light energy into chemical energy. Chloroplasts contain the pigment chlorophyll, which captures sunlight and uses it to transform carbon dioxide and water into glucose and oxygen. This process is vital not only for the plant's growth and energy needs but also for the ecosystem, as it produces oxygen essential for most life forms on Earth. In addition, chloroplasts help in regulating carbon cycling, contributing to the overall balance of ecosystems.