This study investigates how preservice elementary teachers (PSTs) engage and reflect on two science disciplinary practices: engaging with representations and engaging in evidence-based arguments. In the context of elementary science, teachers blend multiple practices across curricular topics and instruction. However, studies of teachers' use of various practices often examine them independently. Contrastingly, here we examine the blending of these two practices with a focus on PSTs' myriad ways of sensemaking about these practices, referred to as "knowledge resources." Data involve audio recordings of PSTs discussing arguments and representations while engaged in small group activities centered on carefully designed teaching cases where the PSTs were tasked to imagine that they are the teacher in an elementary classroom. Analyses reveal that the PSTs used a variety of knowledge resources for analyzing existing representations, generating new representations, and evaluating and generating both existing and new arguments. We also found that PSTs' knowledge resources about arguments and representations were brought together in two ways: generating arguments based on given representations to enhance their understanding and generating representations in response to student arguments to enhance student understanding. These findings are important for teacher education, how PSTs are taught to engage with these practices, and how they conceptualize different instructional strategies for supporting elementary students' understanding and use of these practices.