South Africa has eleven official languages, a multilingual nation in which English is the Language of Learning and Teaching (LoLT) to the majority of learners nationwide. However, the South African education system, continues with teaching and assessing learners in English except for English and Afrikaans speaking learners who are taught and assessed in their mother tongue. The issue of monolingual education in multilingual realities exists in South African classrooms, contributing to high failure rate in the sciences and also restricts learners’ choice of subjects. In a quest of decolonising the curriculum, translanguaging, code-switching and code-mixing form part of the support for learners whose language of instruction is different from their home language by helping them gain a deeper understanding of Life Sciences content knowledge. Teachers from three schools from disadvantaged backgrounds in the Eastern Cape in South African were purposively selected to use code-switching and translanguaging when teaching some topics in Life Sciences to grade 12 learners. Constructivist theory has been chosen as a lens to view the effect of language of learning and teaching in Life Sciences classrooms. Not only did learners improve their understanding of Life Sciences vocabulary but teachers used code-switching effectively to scaffold learners who were unable to grasp the meaning of content knowledge they needed to acquire as a tool to ameliorate their understanding due to language barriers. Furthermore, multilingual glossaries were used to describe concepts from English to the IsiXhosa language which also improved learners’ participation in class and consequently improved the content that was taught. These findings concur with studies reviewed in this study that recommend the mother tongue use for improving learners’ performance in the STEM subjects. Language directly or indirectly affects how knowledge packaged in the curriculum can be taught effectively to English Second Language speakers.The argument contributes to addressing the issue of access to quality education which is one of the UNESCO’s Sustainable Development Goals (SDGs).

Keywords: Language of Learning and Teaching (LoLT), Life Sciences, Translanguaging, Code-switching, Code-mixing, SDGs.