Final answer:
Photosynthesis occurs in the chloroplast, which contains the pigment chlorophyll within its thylakoid membranes. These chloroplasts are found in the mesophyll of plant cells.
Step-by-step explanation:
The cell organelle where photosynthesis takes place is called a chloroplast. In all autotrophic eukaryotes, photosynthesis occurs inside the chloroplast, which can be found in the mesophyll of plant cells. Chloroplasts are composed of a double membrane envelope, including an outer and inner membrane, and contain disc-shaped structures known as thylakoids, where the pigment chlorophyll is embedded. Chlorophyll is essential for capturing light energy, which initiates the process of photosynthesis. Thylakoids are arranged in stacks referred to as grana and are surrounded by a fluid called stroma within the chloroplast.