Final answer:
During organism development, cells differentiate into specialized types with distinct functions, leading to diverse tissues with unique metabolic activities and longevities. The specialization is reflected in the selective expression of DNA, which results in different functional metabolic pathways. Tissues thus remain distinct throughout life due to their specialized roles and metabolic needs.
Step-by-step explanation:
The question "Why do tissues remain different after development in their sets of functional metabolic pathways throughout life?" reflects on the concepts of cellular differentiation and metabolic pathways. During the development of an organism, cells undergo a process of differentiation, wherein they become specialized in structure and function tailored to specific roles within the body. This specialization is due to the selective expression of different parts of an organism's DNA, akin to actors reading from a script, where each cell type reads only the parts relevant to its function.
The longevity of cells in different tissues can be influenced by internal factors, such as their specific metabolic activity and function, and external factors, such as their environmental conditions and the rates of wear and tear they are subject to. For example, muscle and nerve cells tend to have a lifespan that matches the organism's lifetime because they rarely divide and need to provide consistent function throughout life. On the other hand, cells with functions that involve rapid turnover, such as epidermal cells or leukocytes, have much shorter lifespans corresponding to their roles in protection and immunity, respectively.
Tissues are made up of cells that have become permanently committed to these roles, which is why their metabolic pathways remain different throughout life. The differentiation process, which occurs as cells divide and specialize during development, creates a wide variety of cell types with distinct functions necessary for organismal survival. This leads to various tissues with specific longevities and functions that are critical for the organism's overall health and maintenance.