Why yellow leaf does not make food?

Yellow leaves often indicate a lack of chlorophyll, the green pigment essential for photosynthesis. When leaves turn yellow, it can result from nutrient deficiencies, such as nitrogen, or environmental stressors like overwatering or poor light conditions. Without sufficient chlorophyll, the leaf's ability to absorb sunlight and convert carbon dioxide and water into food (glucose) is severely impaired. Consequently, yellow leaves may not effectively contribute to the plant's energy production.