The present study examined how students’ conceptions on photosynthesis had changed after learning with analogy and model. It was expected that students would bring their ideas about raw materials needed, energy used, and the products of cooking food to understand photosynthesis as chemical reaction which composes of the reactants (carbon dioxide and water) and the products (glucose and oxygen). The result revealed that a great number of students (more than 80%) chose carbon dioxide and water as the reactants and glucose and oxygen as the products of photosynthesis after the instruction, even though most of them chose the distracters
presenting alternative conceptions before the instruction. One explanation for this result is that analogy acts as a sense maker, making a new concept intelligible for the students and also a memory aid, when the physical objects or processes are used to explain biological processes (Venville & Treagust, 1996). Students are familiar with cooking food in which they need to use energy to make food from raw materials. This idea can be transferred to understand photosynthesis, since it also needs energy to transform the reactants to the products. Interestingly, students’ understanding about the role of chlorophyll was improved in that chlorophyll is neither the reactants nor the products of photosynthesis. However, there were a number of students who changed their conceptions about the role of chlorophyll to be the alternative one. Some students thought that chlorophyll is irrelevant, because it was neither included in the photosynthesis equation (the target concept) nor cooking food process (analog). From this result, we realized that the students should be cleared not only about the similarity and difference between the analog and the target, but also the concepts related to the target concept.