Reasons:

* Size: Eukaryotic cells are significantly larger than prokaryotic cells. The average eukaryotic cell is about 10-100 micrometers in diameter, while the average prokaryotic cell is about 0.1-10 micrometers in diameter. This difference in size leads to a greater volume and thus a greater weight for eukaryotic cells.

* Organelles: Eukaryotic cells have a complex internal structure with numerous membrane-bound organelles, such as mitochondria, Golgi apparatus, endoplasmic reticulum, and nucleus. These organelles add significantly to the overall mass of the cell. Prokaryotic cells lack these membrane-bound organelles.

* Cytoplasm: The cytoplasm of eukaryotic cells is more complex and contains a greater number of proteins and other macromolecules, contributing to its weight.

* Cell Wall: Some eukaryotic cells, like plants and fungi, have thick cell walls made of cellulose or chitin, respectively, which adds to their weight. Prokaryotic cells have a simpler cell wall made of peptidoglycan, which is less massive.

In summary: The presence of organelles, a more complex cytoplasm, and sometimes a thicker cell wall make eukaryotic cells heavier than prokaryotic cells.