Student Misconceptions of Photosynthesis

Photosynthesis Misconceptions
Student Misconceptions of Photosynthesis: How do Plants Eat?
Marissa L. Mullen
California State University, Northridge
Photosynthesis Misconceptions
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
Photosynthesis Misconceptions
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
Photosynthesis Misconceptions
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 threedimensional model of a chloroplast, acting out the photosynthesis reactions as a role-play
Photosynthesis Misconceptions
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.
Photosynthesis Misconceptions
Driver, Rosalind, Squires, Ann, Rushworth, Peter, & Wood-Robinson, Valerie. (1994).
Making Sense of Secondary Science: Research into Children’s Ideas. London:
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