Multicellular organisms such as plants and animals are composed of millions to a trillion (1,000,000,000,000) cells that work together. The cells that make up different tissues have different shapes and perform different functions for the plant or animal. Even though they have diverse functions, each somatic cell in the organism normally has the same chromosomes and therefore the same genetic makeup. Furthermore, the millions of cells that makeup a mature organism originated from a single cell formed when the male and female gametes from the parents of the organism fused. This single cell established the life of the organism. Understanding multicellular organisms requires an understanding of the lifecycle of the cells that make up the organism.
Development of this lesson was supported in part by Cooperative State Research, Education, & Extension Service, U.S. Dept of Agriculture under Agreement Number 98-EATP-1-0403 administered by Cornell University and the American Distance Education Consortium (ADEC). Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.