To become scientifically literate, students must learn to proficiently utilise and fluently integrate a suite of specialised and contextualised multimodal literacy practices. While the frequency of explicit reading and writing instruction in the sciences is increasing, the wider range of multimodal practices are often not adequately addressed. We explored the multimodal literacy demands and challenges in a first-year biology microscopy practical, using a teaching case-study approach which included a task analysis, evaluation of student reports, and direct observations of students during the practical. The task analysis indicating a substantive level of component and coordinative complexity which required student to use six different literacy practices, and integrate three different modes, necessitating 12 mode switches. Student observations highlighted challenges with identifying cells under the microscope, while analysis of reports provided evidence of students' difficulties with making estimations, producing biological drawings, and appropriately integrating quantitative and qualitative information into their drawings. Underpinning these challenges was the requirement to integrate multiple modes simultaneously. These findings should inform critical reflection on the teaching of multimodal literacy practices and the need to make these practices explicit to students and provide sufficient opportunity for them to develop individual modal fluency, prior to the requirement for multimodal integration.