We present the results of a qualitative research study designed to explore differences in the types of reasoning triggered by information presented to chemistry students in two different formats. One group of students was asked to analyze a sequence of images designed to represent critical elements in the explanation of a target phenomenon. Another group of students was asked to analyze an illustrated text that introduced core concepts and ideas needed to understand the same phenomenon. Our study revealed major differences but also important similarities in student reasoning under the two conditions. Analyses of images led to more descriptive and limited accounts of the phenomenon than the analyses of text. However, these latter analyses often were plagued by conceptual confusions. Mechanistic explanations built under the two conditions frequently invoked a single causal factor as responsible for the phenomenon. Probabilistic effects were consistently neglected in these explanations.