The significance of chloroplasts in green plants lies in their role in photosynthesis. Chloroplasts are organelles that contain the pigment chlorophyll, which captures sunlight to convert carbon dioxide and water into glucose and oxygen. This process not only provides energy for the plant but also produces oxygen as a by-product, essential for the survival of aerobic organisms. Chloroplasts thus help in sustaining life on Earth by contributing to energy flow within ecosystems and playing a critical role in the carbon cycle.