Plant and animal cells are eukaryotic cells. Each one has a cell membrane, cytoplasm and genetic material that is enclosed in a nucleus. The word eukaryote refers to this nucleus.
Bacterial cells are prokaryotic cells. They are much smaller than plant and animal cells. A bacterial cell has cytoplasm and a cell membrane, surrounded by a cell wall. Its genetic material is not enclosed in a nucleus. It is a single DNA loop lying in the cytoplasm, and there may also be one or more small rings of DNA called plasmids.
Cells are tiny, so we use small units. 1 millimetre (mm) is one thousandth of a metre. 1 micrometre (µm) is one thousandth of a millimetre, so 1 µm = 1 × 10-6 m. A typical animal cell is about 10 µm across and a typical bacterium is about 1 µm across. The animal cell is therefore about 10 times wider, which is one order of magnitude (one power of ten) bigger.
