A nucleus is a membrane-bound cell organelle only found in eukaryotic cells.
The membrane of the nucleus is termed as nuclear membrane and the gel-like content inside the nucleus is termed as nucleoplasm.
The nucleus is the controlling center of the cell as it contains DNA or genetic material of the cell.
In contrast, prokaryotic cells are primitive cells which lack membrane-bound organelles like the nucleus, mitochondria, Golgi body et cetera. The DNA of a prokaryotic cell remains suspended in the cytoplasm.
The fossil shows evidence of how animals lived on Earth in the past and shows history about animals that may be extinct now or have evolved since then, which would show development in the animal in the fossil.
