Systemic assessment questions (SAQs) are novel assessment tools used in the context of the Systemic Approach to Teaching and Learning (SATL) model. The purpose of this model is to enhance students' meaningful understanding of scientific concepts by use of constructivist concept mapping procedures, which emphasize the development of systems thinking. In this study, we preliminarily investigated whether specific SAQs forms are potentially valid and reliable tools for assessing 11th grade Greek high school students' meaningful understanding of organic reactions. Thus, we designed and comparatively tested two "fill-in-the blank" SAQs with specific characteristics, differing in their degree of directedness, their cognitive demands, and their systemic diagrams' complexity. The results indicated that SAQs under study have acceptable validity and reliability as evaluation tools for 11th grade high school students. Additionally, the SAQ form that incorporates a more complex systemic diagram and is "less-directed" and more demanding for the examinees was found to be more appropriate for capturing students' meaningful understanding of organic reactions. (Contains 4 tables and 5 figures.)