In biomedical/biological research fields, some semantic data (experiments, evidence, annotation, etc.) can be classified into different levels (from the DNA/RNA level to higher levels such as cells, tissues, organs, and biological systems) based on different degrees of abstraction. Hence, it is important to represent and integrate them across different levels. The purpose of this paper is to address the characteristics of biological data and develop a multi-level conceptual model. Our approach facilitates more accurate modeling of biomedical ontologies, and a better understanding of the data stored in various biological data sources. Furthermore, we propose intra-level and inter-level relationships and give formal definitions illustrated with examples in order to precisely describe relation/behavior among concepts at multiple levels. Our work can be used as the building block for biomedical data or ontologies integration.