Dealing with students’ conceptions is one of the central elements of student-oriented teaching. In order to be able to organise learning processes efficiently, it is necessary to look at the learners in a differentiated way and to approach their conceptions individually. The first necessary step is the individual diagnosis of each student’s conceptions. This article presents a qualitative study (N=8) that focused on the development of drawing assignments for the diagnosis of conceptions on the topic of plant nutrition. Based on the Cognitive Metaphor Theory (CMT), features were identified that are beneficial for the diagnosis of the conceptions. To achieve this goal, it was crucial to reliably diagnose existing conceptions with valid assignments, which can also be carried out in schools. Research about task design and the proceeding diagnosis of conceptions in the light of the Conceptual Metaphor Theory have received little attention so far. This article therefore deals predominantly with the question about the design of assignments in the context of conceptual change. Based on this, guidelines were derived for the design of assignments for practical use in science education. This study represents the basis for developing a Moodle-based digital learning environment for working with students' conceptions on the topic of plant nutrition in schools.