Other scientists concluded that all living things are made of cells and that living cells arise only from preexisting cells. Non scientists like Leeuwenhoek made important contributions. The most fundamental differences in the living world are differences between prokaryotic and eukaryotic cells. The Kingdom Monera includes prokaryotes. 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.