The document compares plant and animal cell structures under a microscope. It notes that one substance observed was prokaryotic (the Elodea plant cell), as it lacked a nucleus, while the single-celled organism was eukaryotic as it contained a nucleus. Both cell types contain organelles like the cytoplasm, cell membrane, vacuole and mitochondria. The plant cell was better suited for study due to its large size and visible cytoplasmic streaming.