A key to understanding why a text is difficult to process: Lexical uniqueness of academic English texts

While the register of English language tertiary textbooks has been investigated substantially, moderately little is explored about the register analytical features of secondary textbooks. The purpose of the present pedagogically-driven study is to analyse the register of biology textbooks for secondary students from the point of view of English as a second language (ESL) teaching by describing the lexical uniqueness of the register of the biology corpus (BIOCOR) 10th-grade students need to process during their studies at a bilingual secondary school. The BIOCOR (consisting of 7,021 words) was compared to a reference corpus (REFCOR) of general English texts at a CEFR B2 level (comprising 7,098 words) by exploring its high-value positive and negative keyness lexical items. The results of the investigation disclose that the lack of specialised uniqueness is prevalent in the BIOCOR with regard to academic English and specific biology terminology. The lexical plainness of the biology textbook can be regarded as one of the linguistic features revealing the non-academic but popularizing nature of the secondary textbook register.