Cell Differentiation and Biological Diversity in Multicellular Organisms

Cell Differentiation and Diversity

Many are unicellular eukaryotic organisms, but the evolution of eukaryotic cells also led to the first multicellular organisms. The development of a multicellular organism is determined by the division, growth, and differentiation of cells.

Every cell in a multicellular organism comes from the splitting of a single initial cell and, therefore, all have the same genetic content. However, despite being genetically identical, not all proteins are equal. All body cells share many proteins, but others are specific to each cell type. This is because the control of protein synthesis is managed by regulating gene expression, which is influenced by various factors, including the modulation exerted by the cellular microenvironment.

Cell differentiation generates different cell types with distinct functions, which implies significant changes in cell morphology. A multicellular organism develops and grows through cell division. However, development control and the regulation of cell numbers throughout a lifespan also require the elimination of cells that are not needed, which is carried out by programmed cell death.

Diversity of Animal Cells

In an animal organism, there are over 200 different cell types that perform a variety of functions. Differentiation and specialization lead to the formation of different tissues:

• Epithelial tissues: Cover and protect internal and external surfaces of the body and perform the exchange of nutrients and secretion of substances.
• Connective tissues: Bind other tissues together to form organs and contain cell types with very different functions.
• Supporting tissues: Provide support and protection to vital organs.
• Blood: Made up of different cell types, such as leukocytes, in charge of defense against infectious agents, or erythrocytes, which transport oxygen to cells.
• Muscle tissues: Composed of elongated cells that have specialized in the role of contraction.
• Nervous tissue: Consists of cells, among which neurons are specialized in the generation and transmission of nerve impulses.

In all these tissues, each cell type adopts a characteristic morphology consistent with the role it will play.