Organization of Tissues
Unicellular organisms, like bacteria and protozoans though made of single cells act as a site for diverse life activities such as digestion, respiration, excretion and reproduction. On the other hand, multicellular organisms, like higher plants and animals, are composed of millions of different types of cells that are grouped into different levels of organization. Multicellular organisms have specialized cells, tissues, organs and organ systems that perform specific functions. In this chapter, you will learn different types of plant and animal tissues and how they are modified to coordinate life activities.
Multicellular organisms usually develop from the zygote. Each zygote divides by the process of mitotic cell division. Repeated cell divisions produce large number of cells which undergo cellular differentiation. The process of cell division and cell differentiation lead to the development of specific organs consisting of specific groups of cells to perform specific functions in the body. Group of cells positioned and designed to perform a particular function is called a tissue. An organ is a structure made up of a collection of tissues that carry out specialized functions for example in plants the root, stem and leaves are organs; wherein tissues of leaves include epidermis, palisade tissue, spongy tissue, xylem and phloem. Similarly in animals stomach for example, is an organ that consists of tissues made of epithelial cells, gland cells and muscle cells.