Ascientist is observing a eukarotic cell and a prokaryotic cell. which structure could she only observe in the eukaryotic cell?

The correct answer would be the nucleus.

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.

some fungi obtain their nutrients from a living host (plant or animal) and are called most biotrophic fungi have fairly narrow host ranges—they are specialized on a limited called rhizomorphs that allow the fungus to grow from one tree to another. ascospores are formed inside a sac-like structure called an ascus. so your answer is a