Here's why:

* Chloroplasts contain the green pigment chlorophyll. Chlorophyll absorbs sunlight energy.

* Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to produce glucose (a sugar) and oxygen. This process happens within the chloroplast.

So, the chloroplast is the powerhouse of the plant cell where sunlight is converted into usable energy in the form of glucose.