The purpose of this study is to investigate the effects of the Engagement, Exploration, Explanation, Extension, and Evaluation (5E) learning cycle, conceptual change texts, and traditional instructions on 8th grade students' understanding of photosynthesis and respiration in plants. Students' understanding of photosynthesis and respiration in plants was measured using the test developed by Haslam and Treagust (F. Haslam, D. F. Treagust (1987) Diagnosing secondary students' misconceptions of photosynthesis and respiration in plants using a two-tier multiple choice instrument, J. Biol. Educ. 21, 203-211). The test was administered as pre-test and post-test to a total of 101 8th-grade students in three intact classes of the same school located in an urban area. The classes were randomly assigned as control and experimental groups. Students in the first experimental group (n ؍ 33) received 5E learning cycle instruction, students in the second experimental group (n ؍ 34) received conceptual change text instruction, and students in the control group (n ؍ 34) received traditional instruction. Attitudes toward science and pre-test scores were used as covariates. A quasi-experimental design utilizing the analysis of covariance showed a statistically significant difference between the experimental and control groups in the favor of experimental groups after treatment. However, no statistically significant difference between two experimental groups (5E versus conceptual change text instruction) was found.Keywords: 5E learning cycle, conceptual change text, photosynthesis, misconceptions.Research on students' understanding of scientific concepts in the past few decades has revealed that students possess several ideas that are at variance with scientifically accepted knowledge. To date, several studies in many countries have investigated students' understanding of different science concepts. Many of these studies have focused on photosynthesis and respiration in plants [1][2][3][4][5][6][7][8]. Briefly, these studies revealed that the majority of students at all grade levels hold misconceptions about plant nutrition, the role of water in plants, the role of leaves in plants, gas exchange, autotrophy, the definition and importance of photosynthesis, the role of light in photosynthesis, the role of chlorophyll in photosynthesis, the relationship between food and energy, and the nature of respiration and energy transformation. For example, Stavy et al.[4] found a well known confusion between photosynthesis and respiration in plants in Israeli students (aged 13-15). More than 60% of their sample regarded photosynthesis as a type of respiration. They believed that plants respired at night in a similar way to animals and also believed, however, that during the day, the process was reversed. The rest of the sample (40%) did not know that plants respire at all. Haslam and Treagust [3] examined 441 Australian students' (grades 8 -12) understanding of photosynthesis and respiration in plants. The results of their study indicated...