Here's why:

* Photosynthesis is the process of converting light energy into chemical energy in the form of glucose (sugar). This process requires chloroplasts, which are organelles found only in plant cells.

* Chloroplasts contain chlorophyll, the green pigment that absorbs light energy.

While other functions like respiration, protein synthesis, and cell division occur in both plant and animal cells, photosynthesis is unique to plant cells (and some bacteria).