The correct answer is A. Chloroplast.
Chloroplasts are organelles found in plant cells and algae that are responsible for photosynthesis. They contain chlorophyll, a green pigment that absorbs sunlight and uses it to convert carbon dioxide and water into glucose and oxygen.
Centrosomes are organelles found in animal cells that are responsible for cell division. They contain centrioles, which are cylindrical structures that help to organize the microtubules that form the mitotic spindle.
Tonoplasts are the membranes that surround the vacuoles of plant cells. They regulate the movement of water and solutes into and out of the vacuole.
Nematocysts are stinging cells found in cnidarians, such as jellyfish and sea anemones. They are used to capture prey.
Therefore, the only option that plays an important role in photosynthesis is A. Chloroplast.