Tissue is a group of similar cells that work together to perform a specific function in an organism. In animals, there are four main types of tissue: epithelial, connective, muscle, and nervous. Each type has unique roles, such as protecting organs, supporting structures, enabling movement, and transmitting signals. In plants, tissue is categorized into two main types: meristematic and permanent. Meristematic tissue is responsible for growth, while permanent tissue provides support and transport of nutrients and water. Together, these tissues are essential for the overall function and health of both animals and plants.