Photosynthesis Misconceptions 1
Student Misconceptions of Photosynthesis: How do Plants Eat?
Marissa L. Mullen
California State University, Northridge
Student Misconceptions of Photosynthesis: How do Plants Eat?
Photosynthesis is an essential concept in biology; it is the key biochemical process that produces energy for life on Earth. Both autotrophic and heterotrophic organisms rely on this chemical process for nutrients. However, this complex chemical reaction that occurs inside the chloroplasts of plants is very difficult for most students to understand. Therefore, there are numerous misconceptions that students have about the process of photosynthesis. One of the most common misconceptions is that plants obtain their nutrients, or “food,” from the soil instead of manufacturing organic compounds through the process of photosynthesis.
Photosynthesis Misconception
Beginning early in education, children are taught that in order to grow, plants need sunlight, water, and soil. Photosynthesis is such a complicated chemical process, and so it is often left out of the education of small children. This simplification of a plant’s life cycle leads to student misconceptions, thinking that “plants get their food from the soil … that ‘food’ for plants is anything taken in from the environment” (Driver, Squires, Rushworth, & Wood-Robinson, 1994, p.60).
Additionally, it is difficult for most students to comprehend the idea of manufacturing food instead; “many children associate the word ‘food’ only with what they identify as being edible” (Driver et al., 1994, p.60). Because humans are heterotrophic organisms, obtaining energy from food that they eat, many students assume that all organisms behave in this manner. A study conducted by Panagiota Marmaroti and Dia Galanopoulou of 290 13-year old Greek students showed that even if students were aware that plants are able to produce food by themselves, these same students also stated that “plants receive all their nutrients from the environment” (2006, p.395). In this study, 80% of students were able to correctly answer the question “Why are plants called autotroph?” but they were unable to relate their explanation to the understanding that photosynthesis produces the organic compounds that plants use for food (2006, p.395).
Origin of Photosynthesis Misconception
The misconception that plants obtain their “food” from the soil is a naïve idea that originates mainly from observation and interaction with the natural world. In fact, it can be traced far back in history. In the 1600s, a Belgian physician named Jan van Helmont sought to determine whether or not plants grew by taking material from the soil. His experiment led to the conclusion that as the plant’s mass increased, the mass of the soil remained unchanged, which shows that plants are not obtaining their “food” from the soil (Miller & Levine, 2007, p.204).
Nevertheless, as children observe the world that surrounds them, they are not aware of the complex reactions of photosynthesis or the results of van Helmont’s experiments. This naiveté leads to misconceptions that “have developed from previous learning experiences which may be personal in nature … and can be very stable and highly resistant to change” (Ross, Tronson & Ritchie, 2005, p.84). In the previously mentioned study by Marmaroti and Galanopoulou, 20% of their students held onto the misconception about how plants are fed, insisting that while plants can produce their own food, plants also receive all their nutrients from their environment (2006, p.401).
Teaching Techniques to Overcome Photosynthesis Misconception
Because students come into school with so many misconceptions, teachers must spend a great deal of time to convince students to change their perspectives. Numerous studies have shown that “students’ naïve conceptions are very resistant to change;” educator’s acknowledgement and understanding of student misconceptions can improve instruction to change these incorrect ideas (Ozay & Ostas, 2003, p.70). Teaching photosynthesis can be complicated, as it is as process with components that cannot directly be observed. To address the misconception that plants obtain their nutrients from the soil, a teacher may want to have his or her students repeat van Helmont’s experiment, growing plants and measuring the mass of the soil and the mass of the plants. Students will be able to observe the increase in the plants’ mass and the consistency of the mass of the soil.
Additionally, there are many laboratory exercises that display parts of the photosynthesis reaction, such as the observation of bubbles being produced on leaf surfaces, showing leaves’ production of oxygen; covering part of a leaf to block it from light absorption; and other similar activities. However, many educators have wondered about the effectiveness of these activities in encouraging understanding, attempting to “relate a macroscopic response … with an abstract, submicroscopic explanation” (Ross et al., 2005, p.84). Science educators have found that when teaching complex concepts, such as photosynthesis, “incorporation of a range of different modalities of learning may help students develop a deeper understanding” (Ross et al., 2005, p.85).
In their paper titled “Modeling Photosynthesis to Increase Conceptual Understanding,” Pauline Ross, Deidre Tronson, and Raymond J. Ritchie describe a very interactive method of teaching photosynthesis. While their photosynthesis instruction began with traditional lecture, they follow up with activities such as making a three-dimensional model of a chloroplast, acting out the photosynthesis reactions as a role-play activity, and small-group discussion to create analogies (p.85-86). Ross, Tronson, and Ritchie found that hands-on, interactive activities “increased [students’] level of enjoyment in this difficult conceptual area” (p.87). Because the production of glucose, the “food” product of photosynthesis, cannot be directly observed, the incorporation of learning strategies that engage students and encourage them to “build conceptual bridges through constructing physical analogies, or models” (p.87) can increase student understanding of this complex scientific process.
References
Driver, Rosalind, Squires, Ann, Rushworth, Peter, & Wood-Robinson, Valerie. (1994). Making Sense of Secondary Science: Research into Children’s Ideas. London: Routledge.
Marmaroti, Panagiota & Galanopoulou, Dia. (2006). Pupils’ Understanding of Photosynthesis: A questionnaire for the simultaneous assessment of all aspects. International Journal of Science Education, March 383-403.
Ozay, Esra & Oztas, Haydar. (2003). Secondary students’ interpretations of photosynthesis and plant nutrition. Journal of Biological Education, 37 68-70.
Ross, Pauline, Tronson, Deidre, & Ritchie, Raymond J. (2005). Modeling Photosynthesis to Increase Conceptual Understanding. Journal of Biological Education, Spring 84-88.