The primary purpose of chloroplasts in plant cells is to conduct photosynthesis, a process that converts light energy into chemical energy stored as glucose. Chloroplasts contain the pigment chlorophyll, which captures sunlight and initiates the conversion of carbon dioxide and water into sugars and oxygen. This not only fuels plant growth but also serves as the foundation for energy flow in ecosystems, as it provides energy for herbivores and, subsequently, carnivores.