Organisms can be divided into two main groups based on fundamental differences in their cell structure. Animals, plants, fungi, and protists are eukaryotes. Bacteria and archaea are prokaryotes. All prokaryotes are unicellular while eukaryotes may be single-celled or multicellular.
The term "prokaryote" refers to single-celled organisms that lack nuclei. The term "eukaryote" refers to organisms that may be single-celled or multicellular, but whose cells are distinguished by nuclei that contain genetic informaiton.
Laws explain what occurs, not why it occurs. This is a law because it states that a limp stalk of celery will become crisp if put into ice water. There is no explanation why or how it occurs, only that it will happen.
