Final answer:
The complexity of multicellular organisms follows a hierarchical structure from atoms to organisms. Specialization and organization into tissues, organs, and systems are crucial for the organism's survival and function. The order from simplest to most complex is cells, tissues, organs, organ systems, and the organism.
Step-by-step explanation:
The order of parts in a multicellular organism, from simplest to most complex, is: cells, tissues, organs, organ systems, and organisms.
Multicellular organisms are an assembly of cells that are differentiated and specialized to perform various complex functions. The fundamental unit of life, the cell, is where the hierarchy begins. Within each cell, atoms come together to form molecules, which in turn form cell components called organelles. These organelles carry out specific functions necessary for cell survival.
When individual cells come together, they form tissues. Tissues are groups of similar cells performing a collective function. These tissues then organize into organs, each of which plays a specific role within the body, such as pumping blood or absorbing nutrients. Organs do not operate in isolation; they form part of an organ system. Examples include the respiratory system, which manages gas exchange, and the nervous system, which controls and coordinates the body's activities.
The highest level of organization is the organism itself, which is the culmination of all the lower levels functioning together holistically. This level of organization is essential for survival, allowing the organism to interact with the environment, reproduce, and perform all necessary life processes. The development of multicellular organisms from a single fertilized egg involves complex processes that regulate cell division, differentiation, and development into a structured and functional organism.