The nucleus is a structure found in both plant and animal cells. It's a fundamental part of all eukaryotic cells (cells with a membrane-bound nucleus), which includes plants and animals.

Here's why:

* The nucleus houses the cell's genetic material (DNA). This DNA contains the instructions for building and maintaining the cell, which are essential for all living organisms.

* The nucleus controls the cell's activities. It regulates gene expression, protein synthesis, and cell division, processes crucial for both plant and animal cells.

So, while plant and animal cells have some distinct differences, the nucleus is a common and essential component in both.