Chloroplasts are the cell structures involved in photosynthesis, with the process commencing at chlorophyll in the thylakoid membranes and the Calvin cycle occurring in the stroma.
The cell structures involved in photosynthesis are chloroplasts. Within chloroplasts, the process begins when chlorophyll, a pigment located in the thylakoid membranes, absorbs light. Thylakoids are stacked into structures known as grana. The space surrounding the grana is called the stroma. Notably, only eukaryotes have chloroplasts.
In contrast, photosynthetic bacteria, such as cyanobacteria, utilize chlorophyll embedded in their plasma membrane rather than in chloroplasts. Furthermore, a component not part of a photosystem, which is essential to the light-dependent reactions in photosynthesis, is ATP synthase. The light-independent reactions, also known as the Calvin cycle, occur in the stroma of the chloroplast.
So, chloroplasts, particularly the thylakoids and stroma within them, are the primary sites of photosynthesis in eukaryotic plant cells. Structures like the nucleus, mitochondria, and ribosomes are not directly involved in the process of photosynthesis.