Multicellular

Multicellular describes organisms that are composed of more than one cell that cooperate, differentiate, and remain integrated through cell communication and adhesion. In multicellular systems, cells organize into tissues and organs with specialized functions, whereas unicellular organisms perform all life processes within a single cell. Multicellularity has evolved independently in several lineages, including animals, plants, fungi, and certain algae and protists.

Key features of multicellular life include cellular differentiation, tissue formation, and the presence of an extracellular matrix that supports structural integrity and signaling. Intercellular communication, via chemical signals and, in some groups, electrical signaling, coordinates growth, development, and responses to the environment. Multicellular organisms typically develop from a single cell, such as a fertilized egg, through tightly regulated gene expression, cell division, and sometimes programmed cell death to shape tissues and organs.

The origin of multicellularity is a major topic in evolutionary biology. It is believed to have arisen more than a billion years ago in multiple lineages, possibly through communities of cooperating cells that later evolved mechanisms for adhesion, communication, and developmental coordination. Cadherin and integrin proteins, among others, are examples of molecular tools that enable cell adhesion and signaling in many multicellular groups.

Advantages of multicellularity include increased size, division of labor among specialized cell types, and the ability to exploit new ecological niches. These benefits are balanced by the need for complex regulatory networks to coordinate growth, nutrient distribution, reproduction, and regeneration.