"Living things are either plants or animals"
Long time, scientists believed that this subdivision were sufficient. Although, as you discover many new secrets of nature, the harder it is that beings that are not animals to be classified as plants. Meanwhile they gave up this system. Creatures are divided into three groups, so-called domains: bacteria, alkenes and eukaryote. The first two groups include beings that live without proper cell nucleus, whose cell development shows structural differences. Eukaryote, by contrast, sums up all living things with cell nucleus and inner or outer skeleton.