CTS Guide: Cycling of Matter in Ecosystems pp 110-111- Section IV Research Summaries
Carbon Cycling and Transformation
Brown and Schwartz (2009): Studies have shown that high school and undergraduate students often struggle to understand the cycling and transformation of carbon. They cannot always account for the movement of carbon between photosynthesis and respiration, and some students think that photosynthesis requires human input of carbon dioxide.
Students have a difficult time imagining plants as chemical systems. In particular, middle school students think organisms and materials in the environment are very different types of matter. For example, some students think plants are made of leaves, stems, and roots and the nonliving environment is made of water, soil, and air. Students see these substances as fundamentally different and not transformable into each other (AAAS 2009).
In a study of 759 15-year-old students who had studied photosynthesis, only 8% could relate photosynthesis to plant growth by describing how a tree makes tissue from the things it takes in from the environment. Only 3 students out of 759 said that tree tissue is made from carbon dioxide and water using light energy to make food. Other studies have also found that students have a difficult time accepting that weight increase and growth in plants is attributed to the incorporation of matter from a gas in the air (Driver et al. 1994).
Barker and Carr (1989) found that many children regarded sunlight as one of the reactants in photosynthesis, along with carbon dioxide and water. Some students consider light to be made of molecules, thus contributing to the matter that makes up a plant.
Cyclical Process
Some middle school students recognize recycling of material through soil minerals but fail to incorporate water, oxygen, and carbon dioxide into matter cycles. Even after specially designed instruction, students cling to the misinterpretation that materials are recycled primarily through soil in the form of minerals (AAAS 2009).
Driver et al. (1994): Many children think that dead things simply disappear when they decay and their matter is not cycled back into the environment.
Smith and Anderson (1986): A study of 12-year-old students found they were aware that there are cyclical processes in ecosystems. However, most of the students thought in terms of sequences of cause-and-effect events where matter was either created or destroyed and then the sequence repeated. They failed to recognize oxygen and carbon dioxide cycles or processes involving food. Their understanding of matter cycling was fragmented.
Conserving Matter
Leach et al. (1992): Found that some students fail to recognize that matter is conserved in the processes of photosynthesis, assimilation of food, decay, and respiration. Students also had difficulty distinguishing between food, matter, and energy.