This study concerns text, language, and learning in a linguistically heterogeneous upper secondary class in Sweden where students aged 16 to 17 are studying biology. One starting point for the dissertation is the importance of language in all school subjects. Another premise is that language as a resource for learning and communication is a high challenge for students who are studying through their second language. The perspectives adopted in the dissertation are those of language and second-language didactics, and of multimodality. The dissertation is based on field notes, audio recordings, collected texts, and interviews. A major question is the extent to which the students are given the potential for coherent meaning making. Another crucial question is how different student groups succeed in the subject of biology, and their potential to move towards the use of more academic language. In the foreground of the study are text analyses in which the notions of intertextuality and recontextualization are an important foundation for understanding, and where textbook, teaching, and student texts are related to each other. The study shows, among other things, the importance of visualization of taxonomic relations, through which connections within a subject can be made explicit. The results also hint at the potential of different visual representations to bridge the gap between everyday and more scientific modes of expression. Mobility between and within discourses can thus be viewed as multimodal. The dissertation also uses the notion of text activities, which can be compared to the Sydney School`s concept of genre. The findings reveal relatively large differences between different chapters in the biology textbook, with regard to text activities, linguistic features, and the degree of multimodality. Differences thus arise in the degree to which these texts are a challenge to the reader. The findings show, moreover, that different images can be regarded as visual text activities and can thus be analysed on the level of text structure. The discrepancy between different student groups in the class is relatively large. The second-language students rarely achieve high grade levels. Lower grades, in turn, mean that standards are set relatively low for written work, and there is also strong teacher mediation at this level. Higher grade levels, on the other hand, require more advanced text activities and more independent reflexive writing and reading. The latter indicates a need for explicit metadiscursive discussions in the classroom. The results also suggest a need for broader language and text production, especially for second-language students.