Simple tissues are groups of similar cells that perform a specific function in plants and animals. In plants, simple tissues include parenchyma, collenchyma, and sclerenchyma, each serving roles in storage, support, and protection. These tissues are composed of one type of cell, making them distinct from complex tissues, which contain multiple cell types. In animals, simple tissues are categorized into four main types: epithelial, connective, muscle, and nervous tissues. Each type has a unique structure and function, such as covering surfaces, providing support, facilitating movement, and transmitting signals. Simple tissues are essential for the overall functioning of organisms.