[1]
Navigating this Part of the Pathway
This part of the pathway provides students with experiences that allow them to come up with a final answer to the overall driving question: Why are the fish dying in Sunrise Farm Pond? First, students consider and illustrate ways in which the organisms in a farm pond are important to each other. Next, using their emerging understanding of the importance of abiotic factors and their knowledge of organisms’ needs for survival, students examine the interconnectedness of these components using a food web model. Finally, students refine their cross-sectional pond models to reflect their improved understanding of what is causing the fish in the pond to die.
The food of almost any kind of animal can be traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants. Some organisms, such as fungi and bacteria, break down dead organisms (both plants or plants parts and animals) and therefore operate as “decomposers.” Decomposition eventually restores (recycles) some materials back to the soil. Organisms can survive only in environments in which their particular needs are met. A healthy ecosystem is one in which multiple species of different types are each able to meet their needs in a relatively stable web of life. Newly introduced species can damage the balance of an ecosystem.
Connections to Other Pathway Parts
Part Three of the pathway builds on the ideas discussed in Part Two and serves to connect the initial disturbance (i.e. fertilizer runoff) with the outcome (i.e., fish dying). The three pathway parts together represent the natural sequence of events that occurs when a pond is overloaded with nutrients. Therefore, all parts should be included in instruction and done in order.
Teacher Content Background
Because decomposers use oxygen as they consume dead organisms, the levels of oxygen in the pond decrease as the decomposers consume dead algae. In addition, algae block sunlight from reaching underwater producers [3], which makes it harder for the producers to make oxygen. For both reasons, oxygen levels in the pond go down, and other organisms are not able to survive. Initially, some organisms (e.g., perch) may move to other areas of the pond with more oxygen; however, their food sources (e.g., mayfly larvae, minnows) will also decrease because they have less oxygen. With limited food sources, some perch will die.
Student Thinking:
- Upper elementary students often hold many misconceptions related to the feeding behavior of organisms in an ecosystem.
- Students often view organisms as dependent on humans (Demetriou et al., 2009; Leach et al., 1992, 1996b). The idea that organisms rely on humans may result from students’ everyday experiences, particularly those in a garden, home, or zoo setting, which may reinforce this notion that organisms could not survive without human intervention.
- Students also tend to believe that organisms consume all others below them in a food web (Grotzer, 2009; Hogan, 2000; Özkan et al., 2004). A top-level consumer, for example, would be seen as having all other organisms in the ecosystem as a food source. Relatedly, students think that organisms choose from among many options in selecting their prey or easily change their diet based on food availability (Grotzer, 2009; Hogan, 2002; Leach et al., 1992; Tsoi, 2011). It is possible that these ideas arise from students’ own experiences of selecting food at a grocery store or restaurant.
- Students conceptualize food web relationships at the individual level (e.g., a single predator animal and a single prey animal), as opposed to the population level (Bell-Basca, Grotzer, Donis, & Shaw, 2000; Grotzer, Basca, & Donis, 2011; Leach et al., 1996b). For example, students may envision a relationship as one perch consuming one minnow, as opposed to the perch population feeding on the minnow population.
- Students also appear to hold naïve conceptions related to abiotic factors. These factors include, but are not limited to, light, temperature, moisture, amount of oxygen, nutrient availability, and salinity.
- Students often do not recognize non-living factors as part of an ecosystem (Brody, 1993, 1994; Magntorn & Helldén, 2007; Özkan et al., 2004).
- Students commonly believe that organisms are not affected by abiotic factors (Adeniyi, 1985; Brody, 1994; Leach, Driver, Scott, & Wood-Robinson, 1996a).
- Some students may suggest that abiotic factors affect all organisms equally (Hogan, 2000).
- Students may not recognize natural, biodegradable, or non-visible entities as pollutants (Brody, 1994).
- Students may view abiotic factors as unchanging (Brody, 1993). For example, they may overlook seasonal differences (e.g., changes in water temperature throughout the year).
- Students often appear uncertain about the range of connections existing in food webs.
- Trying to understand “underlying causal patterns” can be difficult for elementary-age students (Grotzer & Basca, 2003; Grotzer, Basca, & Donis, 2011). Students think populations are affected only by those directly linked in a food web (Bell-Basca et al., 2000; Grotzer, 2009; Grotzer, Basca, & Donis, 2011; Hogan, 2000, 2002; Hogan & Fisherkeller, 1996; Magntorn & Helldén, 2007b; Özkan et al., 2004; Tsoi, 2011).
- Similarly, students tend to overlook indirect effects of abiotic factors on organisms and their feeding relationships, such as the extended impacts of pollutants on an ecosystem (Hogan, 2000).
- Students’ understandings also appear somewhat limited when examining the direction of effects (Gotwals & Songer, 2010; Hogan, 2002; Leach et al., 1996b). For example, students are more likely to trace effects up through a food web rather than down.
- Students view ecosystems as universally fragile, believing that a food web disturbance would affect all populations similarly (Grotzer, 2009; Özkan et al., 2004).
Student Experiences
Student Experience 1: Who consumes who in Sunrise Farm pond? [4] (Students collectively draw on existing knowledge to identify trophic relationships among pond organisms.) 5.LS2.A [2]
Student Experience 2: What happens if organisms’ needs aren’t being met? [5] (Students revisit concepts from Part One and Part Two to identify organisms’ needs in order to determine how a disturbance will impact various organisms.) 5.LS2.A [2] CCC: Cause and Effect [6]
Student Experience 3: In what ways are organisms being affected in Sunrise Farm pond? [7] (Students take on the roles of populations within Sunrise Farm pond and illustrate these connections using a string web. Students then use this model to simulate the effects of a disturbance to an ecosystem.) 5.LS2.A [2] SEP: Developing and Using Models [8] CCC: Cause and Effect [6]
Student Experience 4: How should we revise our pond model? [9] (Students revisit the mystery at the Sunrise Farm pond and revise their models based on new ideas.) 5.LS2.A [2] SEP: Developing and Using Models [8] SEP: Constructing Explanations [10] CCC: Cause and Effect [6]
Student Experience 5: The whole story [11] (Students hear the last part of the story of the Mystery at Sunrise Farm Pond and discuss how it relates to their pond models.) 5.LS2.A [2] SEP: Developing and Using Models [8] SEP: Constructing Explanations [10] SEP: Asking Questions [12] CCC: Cause and Effect [6] CCC: Stability and Change [13] CCC: Systems and Systems Models [14]