A scientist was observing an unknown slide under an electron microsocope; he found a cell without a well-defined nucleus but with a thick cell wall and ribosomes. What type of cell could it be?

Prokaryotic

Eukaryotic plant cell

Eukaryotic animal cell

The difference between eukaryotic cells and prokaryotic cells is that Eukaryotic cells have a "true" nucleus containing their DNA, whereas prokaryotic cells do not have a nucleus.

Animal cell have defined cell wall. so according to above explanation,

Prokaryotic, is the right answer.