Most photosynthetic cells in plants are found in the leaves, specifically within the mesophyll tissues. The chloroplasts that carry out photosynthesis are concentrated in the parenchyma cells of the leaf mesophyll, making leaves the primary sites of photosynthesis in most plants. Key points:

• Chloroplasts are the organelles where photosynthesis happens [source: Britannica on chloroplasts and leaf mesophyll].
• While chloroplasts can be present in green tissues throughout a plant, the highest density is in the leaf mesophyll, which maximizes light capture and gas exchange for photosynthesis.

If you’d like, I can pull specific sources or diagrams to illustrate chloroplast distribution in leaf anatomy.