what is the largest cell structure

Nucleus: The largest organelle in the cell, which contains DNA and other cell's hereditary information. The main role of nucleus in animal cell is it controls all cellular activities. Vacuole: They are the fluid sacs, which are present in less numbers in animal cells compared to plant cells.
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plant cell

The nucleus is the largest cellular organelle in animal cells. In mammalian cells, the average diameter of the nucleus is approximately 6 micrometres (µm), which occupies about 10% of the total cell volume

Nucleus

Nucleus and vacuoles can differ

nucleus

nucleus

Nucleus in animal cell and vacuole in plant cell