Flagella

Flagella are long protusions on the back of a cell such as the tail of the sperm cell. They can propel a cell through liquid or fluid mediums via their undulation and fluctation. Eukaryotic flagella are enlongated versions of cilia whereas bacterial flagella are completely different both in structure and mechansims . 

Bacterial flagella are made entirely of protein and have a diameter of around 12-30nm. Several thousand protein subunit molecules of Flagellin make up one bacterial flagellum, of these molecules there are two types. Three types of flagella arrangement are understood to occur: monotrichous, peritrichous and lophotrichous. Monotrichous flagellum are single and Polar, a peritrichous arrangement occurs with flagella over the entire cell surface, whilst lophotrichous arrangements occur when there are many polar flagellum .