This paper investigates Lebanese grade 7 biology teachers' mathematical knowledge and skills, by exploring how they explain a visual representation in an activity depending on the mathematical concept "Function". Twenty Lebanese in-service biology teachers participated in the study, and were interviewed about their explanation for the designed activity. The data analysis reveals that teachers refer to different entities as constituting models, and express different way far away from the mathematical concept "Function". Based on the collected data, the findings could not be generalized to all biology teachers, but it is safe to conclude that it would be enriching for students if biology teachers had a background in mathematics and mathematics education, in order to deal with situations of exploration and analysis of the different constraints that might affect biology activities. In addition, the results highlight the need to review the teachers' preparation programs in a way that considers integrating mathematics into sciences, as well as a need to introduce a reform to the Lebanese Biology curriculum, in order to explicitly include all the mathematical competencies required to build up scientific knowledge.