This paper explores classroom discourse patterns of perceived difficult topics in biology such as classification, mitosis and meiosis at senior secondary level. A collective case study design was used and data were obtained from students and teachers using observation schedules and interview guides. Purposive sampling was used to select the sample from the target population. Data collected were analysed using discourse analysis and thematic analysis. The study found out that three discourse patterns were used during lessons on topics perceived to be difficult .These three discourse patterns include: Pupil to pupil discourse pattern, teacher led discourse pattern and teacher explanation discourse pattern. The choice of discourse patterns by teachers hinged on the following: non availability of teaching aids, desire to cover more content, engagement of pupils in the lesson, need to relate lessons to real life situations, skill in managing groups, pupil participation and need to provide concrete examples. The inappropriate use of the discourse patterns made understanding of stages of cell division and biological names of living organisms difficult to pupils. Some of the recommendations made were that: Teachers should combine the three discourse patterns namely teacher explanation, teacher led and pupil to pupil discourse patterns when teaching biology because these patterns proved effective when used together. Teachers should avoid using one discourse pattern during lessons on topics perceived to be difficult. Workshops and seminars should be organised for teachers to enable them acquire skills of teacher explanation, teacher led and pupil to pupil discourse patterns for teaching biology.