Here's why:

* Chlorophyll is a pigment found in plants and some algae. It's the key component in photosynthesis, the process by which these organisms use sunlight to convert carbon dioxide and water into glucose (sugar) for energy.

* Animal cells are heterotrophic, meaning they obtain their energy by consuming other organisms (plants, animals, or their byproducts). They do not have the necessary structures (chloroplasts) or pigments (chlorophyll) to perform photosynthesis.

* Mitochondria are the powerhouses of animal cells. They break down food molecules (glucose) through cellular respiration, releasing energy in the form of ATP.

So, while plants use chlorophyll for energy production, animal cells rely on a different process to fuel their activities.