Plants is one of six units in the Carbon: Transformations in Matter and Energy (Carbon TIME) curriculum, which was developed through an NSF-funded research collaboration focused on learning progressions to support environmental literacy. These units were developed for middle and high school students. The units are designed in three groups; each group increases in scale from the previous one. Students should first complete the foundational unit, Systems & Scale (http://carbontime.bscs.org/systems-and-scale), which uses the process of combustion to build basic concepts of matter, energy, and organic compounds at the atomic-molecular scale. The Plants unit is one of three units at the organism level, and it is intended that students complete one or more of these three units. These units are intended to be followed by one or both units at the systems level. Each organism scale unit focuses on three questions: (1) Where are molecules moving? (2) How are atoms in molecules being rearranged into different molecules? and (3) What is happening to energy? In the Plants unit, students investigate two phenomena related to plant growth: (1) the change in mass during plant growth over time and (2) gas exchange during plant growth in light and dark conditions. The highly guided sequence of six lessons in the unit helps students identify patterns from their observations, develop a model for plant growth, and then apply that model to explain the growth of radishes and other plants. This model includes photosynthesis, biosynthesis, and cellular respiration. The unit includes the option for a simpler growth protocol that requires a two-week growth period or a more advanced protocol that requires a four-week period. Extensive supporting infomation is provided within each lesson and on the reources page (http://carbontime.bscs.org/resources). The assessment site (http://ibis.colostate.edu/MSP/CTIME/Index.php) includes pre/posttests for each unit and for the overall curriculum. The overview provided here (http://media.bscs.org/carbontime/files/unit_synopses.pdf) provides a helpful orientation to this complex resource.