The other four kingdoms, Protista, Fungi, Plantae, and Animalia, are eukaryotic. Eukaryotic cells have internal membranes that surround the nucleus and other internal structures. In multicellular eukaryotes, cells may specialize for given tasks. Cellular specialization leads to specialization of tissues, organs, and organisms. V. Cells vary in size and number in organisms A. Most cells are small.
Prokaryotes are the smallest cells.
The largest animal cells include ostrich eggs and giraffe nerve cells. All cells must perform certain tasks. The cytoplasm must be separated from its environment so appropriate internal conditions can be maintained. The cell must take in raw materials and expel wastes through the barrier that separates it from its environment. It must take in energy and convert it to a form useful for powering the cellular machinery.