Which structure is unique to plant cells

There are a few differences between animal cells and plant cells.
Plant cells have cell walls, and animal cells do not.
Plant cells have a large central vacuole and animal cells do not.
But probably the most recognizable (and probably the one your question is asking about) is the chloroplast. The Chloroplast is the home of chlorophyl, a green pigment plants use to make energy.

This is the most closely resembles the model.