This unit contains three lesson sets associated with three key organelles: mitochondria, nucleus, and chloroplasts (in plants). Each lesson set engages students in figuring out the function of the organelle under study using evidence. Students either evaluate different alternative models of the organelle’s function or develop a model of the function themselves.

The mitochondria lesson set spans about 2-3 instructional days (assuming 45 min periods). In this lesson students encounter two alternative models for mitochondria function: a) the movement model argues that mitochondria help the cell physically move in its environment, and b) the energy model argues that mitochondria help to generate energy for use by different cell parts. Students work with six pieces of evidence to figure out which model is a better explanation of the mitochondria’s cellular function. Evidence varies from credible scientific studies (high quality) mitochondria in mice tissue samples, to un-credible anecdotal advise from a beautician about mitochondria and skin aging (low quality evidence). Students rate the quality of the evidence pieces and relate each piece to the two models using the MEL matrix. They then use the MEL to support the construction of an evidence-based argument for the better model.

The nucleus lesson set spans about 3-4 instructional days and present students with two alternative models of what the nucleus does: a) control center--the nucleus is the control center of the cell and the DNA in the cells gives orders to other parts of the cell telling them what to do, and b) carries instructions—the nucleus contains DNA which contains instructions for making different chemical structures, these structures do different functions in the cell. While the control center model is compelling it is misleading in that the nucleus does not directly “tell” other parts of the cell what to do (this model may even appear in textbooks). The instructions model, in contrast, does not anthropomorphize the nucleus and provides a mechanism by which genetic instructions can impact cell structures and function. Viewing genes and DNA as instructions is an important steppingstone to understanding more complex ideas about heredity and cellular function. In this lesson set students work with a variety of evidence (e.g. exploring how scientists genetically engineered cats to glow in the dark; using bacteria to make human insulin to treat diabetes) to decide which model better explains the available evidence. Students again use the MEL matrix to support the construction of an evidence-based argument for the better-supported model.

The chloroplast lesson set is approximately 4-5 instructional days. In this lesson set students use evidence to construct and revise a model of chloroplast function. In this lesson set students collect some of the evidence themselves using Elodea plants, and use computers simulations of scientific studies as additional pieces of evidence. Students use four pieces to develop their initial model and then revise this model based on two additional pieces of evidence. To conclude the lesson, students write an evidence-based explanation of their final model.

Download the main lessons of the Cells unit (22 MB)