Final answer:
The highest level of structural organization in biology is the organismal level. This represents a complete and functioning living being, including all subsidiary levels such as the cellular, organ and chemical levels.
Step-by-step explanation:
In the hierarchical organization of life, the organismal level is the highest level of organization. This level, option d.), includes entire living things, that are capable of performing all the functions necessary for life. The other options mentioned, such as cellular, organ, and chemical levels, are the sub-levels of structural organization that build up to create an organism as a whole. Each of these levels have their unique roles, but it is the organismal level that comprises all these lower levels and represents a complete, functioning individual. The highest level of structural organization is the organismal level. At this level, all of the systems and organs in an organism work together to maintain its functions and survival. The organismal level includes complex interactions between different organs and organ systems.
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