Here's why:

* Chloroplasts are the organelles within plant cells that contain chlorophyll. Chlorophyll is the pigment that absorbs sunlight, which is the energy source for photosynthesis.

* Photosynthesis is the process where plants use sunlight, water, and carbon dioxide to produce their own food (glucose) and release oxygen.

* Animal cells do not have chloroplasts and therefore cannot perform photosynthesis.

Let me know if you have any more questions!