Final answer:
Complexity is highest at a high level of integration in biological systems, particularly when endosymbiosis occurs, leading to highly complex eukaryotic cells. Input of energy is required to counteract entropy and maintain biological complexity.
Step-by-step explanation:
The question addresses the concept of integration in the context of biological complexity. Integration can be understood as the degree to which different parts or levels of a biological system work together to form more complex structures and functions. In biology, complexity is highest at a high level of integration. This is because, as systems become more integrated, they exhibit increased complexity due to the interactions between their various components, which can include cells, tissues, organs, and organ systems. When systems reach a high level of integration, such as in the eukaryotic cells where endosymbiosis has occurred, they tend to demonstrate sophisticated structures and functions that are not present in less integrated systems. In the case of endosymbiosis, the integration of formerly independent organisms (like mitochondria and chloroplasts) into a host cell created a highly complex eukaryotic cell with advanced capabilities. As for entropy, which is a measure of disorder, it is counteracted by input of energy. Organized systems, such as living organisms, maintain their complexity by consuming energy to create and maintain order against the natural tendency towards disorder, or entropy.