Tissue structure refers to the organization of cells that work together to perform specific functions in living organisms. There are four main types of tissues in animals: epithelial tissue, connective tissue, muscle tissue, and nervous tissue. Each type has distinct characteristics and roles, such as protecting organs, supporting the body, enabling movement, and transmitting signals. In plants, tissue structure is categorized into meristematic tissue and permanent tissue. Meristematic tissue consists of undifferentiated cells that can divide and form new tissues, while permanent tissue is made up of differentiated cells that have specific functions, such as xylem for water transport and phloem for nutrient distribution.