Here's why:

* Chloroplasts are organelles found within plant cells (and some algae).

* They contain chlorophyll, a green pigment that absorbs light energy, primarily in the red and blue wavelengths.

* This absorbed light energy is used to power the chemical reactions of photosynthesis, which convert carbon dioxide and water into glucose (sugar) and oxygen.

So, while the entire plant cell participates in photosynthesis, it's the chloroplast that specifically captures the light energy to make it happen.