CTS Guide: Cycling of Matter and Flow of Energy in Ecosystems pp 108-109- Section IV Research Summaries
Food Chains and Food Webs
Çinar (2015): Word association tests were used with pre-service student teachers. When given the term “food chain”, the student teachers referred most often to energy flow. When asked what words they associated with the matter that flows through a food chain, none of the student teachers referred specifically to carbon, though most mentioned carbon dioxide, carbohydrate, oxygen, protein and fat; only one mentioned nitrogen.
DeBoer et al. (2014): Researchers found a lack of distinction between matter and energy when U.S. students were asked to construct food web diagrams. Some students included the sun in a food web diagram that was supposed to show the transfer of matter, while others did not include the sun in an energy flow diagram.
Needham (2014): Food chains and food webs have traditionally been associated with ideas about the flow or transfer of energy through an ecosystem. It is important to be aware that when teaching about food chains and food webs, there is the potential to create or reinforce misunderstandings about energy. For example, teaching that the arrows in a food chain/web diagram represent energy transfers; although correct, could create or reinforce the misunderstanding that energy is a substance. It is important for students to understand that what is transferred between populations when organisms are eaten is biomass, which is matter, and that energy is made available for life processes when some of the consumed biomass is used as a fuel for cellular respiration in the cells of the consumer.
Allen (2010): Interpretation of the arrows in food chains was commonly meant to mean “eats”.
Flow of Energy
·Various studies have shown that students have limited knowledge of how energy flows through a food web and that energy is a challenging concept for understanding fundamental ecological processes. Understanding representations is key to understanding how energy flows (Wernecke et al. 2018).
Beals et al. (2012): Both students and teachers have been found to believe that energy can be recycled (e.g., by decomposers) and reused (e.g., by plants) in an ecosystem. The confounding of energy flow and matter cycles was commonly found in their study.
Gotwals and Songer (2010): Found that, when middle and high school students in the United States, Australia, and Canada considered a food chain or web, they could describe feeding relationships between the organisms but did not realize that the arrows represented energy transfer in the system.
Driver et al. (1994): Some students consider ‘stronger’ organisms such as predators as having more energy which they use to feed on ‘weaker’ organisms which they regard as having less energy. The researchers also found that students tend to use accumulation reasoning to explain what happens to energy as it flows through a foods chain. They believe the energy adds up so that a top predator would have all the energy from the organisms that came before it in the food chain.
Gaylord (1986): A study of 17- and 18-year- old biology students revealed that many students thought that energy flows from place to place and is stored like a material. They thought energy was either created or destroyed in biological processes rather than converted and conserved.
Research reveals three commonly held ideas about energy transfer: 1) some students think that the top predator gets all of the energy from the trophic levels beneath it, 2) energy is cumulative as you move up a food chain or food web., and 3) no energy is lost between trophic levels ( Griffiths and Grant 1985).
Matter and Energy
Because middle and high school students learn that energy is conserved, like matter, they often think it must also be recycled like matter (Anderson and Doherty 2017).
A common middle and high school students’ biological idea of energy is that it is anything that enables life; thus, they often refer to “matter and energy cycles” with energy and matter both cycling through soil nutrients. During decomposition they typically see energy as being recycled in the form of nutrients that are released for plant growth, rather than energy that a decaying plant provides to decomposers. Energy during decomposition is sometimes confused with minerals and nutrients (Jin and Anderson 2012; Rice, Doherty, and Anderson 2014).
Studies have shown that middle and high school students tend to think that matter is converted into energy and energy is converted back into matter. They describe this “cycling” of matter and energy as energy and matter being recycled through soil nutrients. (Jin and Anderson 2012).
Leach et al. (1996): 16-year-old students in England were found to frequently used the terms “energy,” “matter,” “food,” and “nutrients” interchangeably in the context of ecosystems.
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.
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.