Cell movement: refers to all movements shown by cells, such as flagellar movement of bacteria; Deformation movement of amoeba and leucocyte; Ciliary movement of paramecium; Flagella movement of euglena and sperm; The protoplasm flow of plant cells and myxomycetes; Contraction of smooth muscle and striated muscle; Chromosome movement and cytoplasmic depression during cell division.
System classification
According to the classification of microstructure and types of contractile proteins, cell movement can be divided into the following three categories:
Flagellin system
The flagellum of bacteria is a spiral thin tube with a diameter of 12-21 nm, which is composed of flagellum protein of spherical protein. It does not contain ATPase;
Tubulin system
Except bacteria, flagella and cilia of animal and plant cells basically have the same structure. Microtubules with a diameter of 20-25 nanometers, which are composed of globular protein tubulins, are regularly arranged. Tannin egg white with ATPase activity is also attached to these microtubules
Actin
Myosin System: Actin and myosin are involved in the movement of amoeba, leucocyte, myxomycetes, smooth muscle and striated muscle. Actin is widely distributed in these cells in the form of microfilaments with a diameter of about 8 nanometers. In striated muscle, actin exists in band I in the form of filaments, but in other cells, actin exists in the surface of protoplasm in bundles composed of dozens to hundreds of fibers. It is generally believed that myosin with ATPase activity exists in the A-band in striated muscle in the form of thick filaments with a diameter of about 15 nanometers, but in other cells, it exists in the form of smaller polymers. 
