The excess of curriculum content is a well-known problem in high school biology. Some strategies to adjust the amount of content to the available classroom time have been proposed, but none has been widely accepted and applied. Furthermore, biology is frequently presented in high school not as an integrated science, but as a collection of unrelated sub-areas, say, zoology, botany, physiology, genetics, and evolution. In this paper, we advance a proposal on how to develop non-arbitrary, clear criteria for selecting conceptual content to be taught and learnt in order to make the biology high school curriculum more integrated and less loaded with content. We argue that we should adopt the idea of structuring concepts for seizing the prominent role some ideas play in biological thinking. We discuss how a hierarchical conceptual framework of biology can help us to identify key concepts as well as connections between these concepts that can allow students understand sub-areas of biology. We also advocate for establishing a balance between the concepts from functional and evolutionary biology, on the one hand, and concepts representing (i) systemic components, (ii) processes, and (iii) descriptive elements, on the other hand. Finally we exemplify how these criteria can be applied by providing a proposal for structuring concepts of biology as a whole and the theory of evolution in particular.