The correct response is:
Plant cells due to the observation of chloroplasts.
This is because the presence of chloroplasts is a defining characteristic of plant cells, as they are responsible for photosynthesis. Mitochondria can be found in both plant and animal cells, while ribosomes are present in all cell types. Prokaryotic cells do not contain a nucleus or chloroplasts. Therefore, the presence of chloroplasts indicates that the cells being observed are from a plant organism.