Navigating this Part of the Pathway
This part of the pathway provides students with experiences that allow them to begin to piece together an answer to the overall driving question: Why are the fish dying in Sunrise Farm Pond? Prior to beginning Part One of the mystery, teachers will have already set up the experiments that require time for growth. Students have recorded daily observations of growth for about three weeks (except for weekends), but will not discuss their observations until instructed to in Part One.
After this preliminary growth period, the pathway starts with students considering which organisms are likely to be in a farm pond. Then students are introduced to the problem with the pond, which they will use as a basis for exploring interdependence in ecosystems. Students make initial models using a cross-sectional pond template to make predictions about what causes the fish in the pond to die. Using the experiments set up in advance of the unit and their observations, students compare growth of algae in jars of pond water with different amounts of nutrients and monitor growth of seedlings in different conditions (or engage with a simulation) to investigate what plants need to grow. Finally, students revisit their cross-sectional models and make revisions using their emerging understanding of how abiotic factors (i.e., non-living factors such as oxygen, water, or nutrients) affect the growth of producers and how producers influence their environments.
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 plant 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.
The energy released [from] food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water).
Plants acquire their material for growth chiefly from air and water.
(NGSS Lead States, 2013)
Connections to Other Pathway Parts
Part One of the pathway lays the foundation for the other two parts, and, much like the relationships that tie together organisms within an ecosystem, this part of the pathway is linked by cause and effect to the other two parts. The three pathway parts together represent the natural sequence of events that occurs when a pond is overloaded with nutrients. Therefore, all pathway parts should be included in instruction and done in order.
Teacher Content Background
- The food of almost any kind of organism can be traced back to producers such as plants and algae.
- Food provides organisms the materials and energy they need to grow and function.
- Producers make their own food inside themselves using energy from the Sun, and matter from air and water.
- Organisms can survive only in environments in which their particular needs are met.
- Environmental conditions include, but are not limited to, light, temperature, moisture, amount of oxygen, nutrient availability, and salinity.
- Natural events and human activity can change the balance or stability of an ecosystem.
- When the balance, or stability, of an ecosystem changes, the opportunities for different types of organisms to meet their needs can increase or decrease.
When humans apply fertilizer containing nitrogen and phosphorus, they alter the balance of the pond ecosystem. These chemical nutrients are not food, but the pond’s producers use them to make components they need to grow. When plants including algae (which are common to many bodies of water, including farm ponds), have plenty of these nutrients, they can better take advantage of sunlight to make their food (i.e., sugar) from water and carbon dioxide. With abundant food, the algae grow much more rapidly and reproduce much faster than before. The increased growth of algae makes the water cloudy, preventing sunlight from reaching the deeper areas of the pond. The lack of sunlight reaching plants below the pond surface prevents them from making enough of their own food to support their growth. These plants can no longer provide their typical steady supply of oxygen to the pond water.
Although producers living in water can look very different from most plants growing on land, they all make their own food and have the same fundamental requirements for this process: sunlight, air (particularly carbon dioxide), and water.
Student Thinking
Students have many misconceptions about producers and their interactions with abiotic factors. For example, students often think that:
- producers take in food from their surroundings (e.g., the soil), as opposed to making food (Adeniyi, 1985; Barman, Stein, McNair, & Barman, 2006; Brody, 1993; Çetin, 2007; Helldén, 1998; Hogan, 1994; Hogan & Fisherkeller, 1996; Leach, Driver, Scott, & Wood-Robinson, 1992; Özkan, Tekkaya, & Geban, 2004; Simpson & Arnold, 1982b; Smith & Anderson, 1984)
- light enhances plant health but is not essential (Smith & Anderson, 1984)
- fertilizer is food for plants (Keeley, 2012; Smith & Anderson, 1984)
- plants do not live in water (Adeniyi, 1985; Brody, 1993, 1994; Brody & Koch, 1990)
- plants exist only to make food for animals that eat plants (Keeley, 2012)
- humans are producers because they prepare their own food
Some students do acknowledge that producers make food for their own growth; however, they tend to have an incomplete understanding of the process, often omitting one or more of the essential components (i.e., light, carbon dioxide, and water) needed to produce food (Barman et al., 2006; Helldén, 1998; Simpson & Arnold, 1982a; Smith & Anderson, 1984). Some may realize that fertilizers are used to help plants grow but not understand that they are non-food chemical nutrients.
In addition, students’ general lack of familiarity with producers growing in water makes it difficult for them to fully understand the needs of such producers. For example, many students think that underwater aquatic plants (e.g., seaweed) do not need light to grow (Brody, 1993, 1994; Brody & Koch, 1990). Some simply do not have any conception of dissolved gases (as opposed to bubbles in liquid), such as oxygen or carbon dioxide, being present in water (Brody, 1994).
Students also often hold incomplete or inaccurate ideas about how humans interact with ecosystems. For example, some think that plants generally need human care to survive. Students may also think that pond organisms (e.g., ducks, fish) depend on humans for food (Demetriou et al., 2009; Leach et al., 1992; Leach, Driver, Scott, & Wood-Robinson, 1996b). Some students may have one of two extreme views of human influence on ecosystems:
- All change in ecosystems is caused by humans and is bad. For example, some think that fertilizers are universally toxic (Gunckel, 1999; Hogan, 2000). Or
- Human activity is separate from ecosystem function.
Finally, some students think that the bigger an organism, the more important it is in an ecosystem. They may have difficulty grasping that small (particularly microscopic) organisms can have important effects (Hogan, 2002).
Student Experiences
Student Experience 1: What lives in a farm pond? (Students collectively draw on existing knowledge to identify pond organisms.)
Student Experience 2: How can we represent what happened at Sunrise Farm Pond? (Students consider the mystery at Sunrise Farm Pond and make an initial model to predict the causes.) 5.LS2.A SEP: Asking Questions SEP: Developing and Using Models CCC: Cause and Effect CCC: Systems and System Models
Student Experience 3: What happens when nutrients are added to pond water? (Students address the effects of fertilizer added to jars of pond water.) 5.LS2.A 5.LS1.C SEP: Analyzing and Interpreting Data CCC: Patterns CCC: Cause and Effect
Student Experience 4: What do plants need to grow? (Students examine plant growth under several conditions to determine what plants need to grow.) 5.LS1.C 5.PS3.D SEP: Constructing Explanations CCC: Patterns
Student Experience 5: How should we revise our pond models? (Students revisit the mystery at Sunrise Farm Pond and revise their models based on new ideas.) 5.LS2.A SEP: Developing and Using Models SEP: Constructing Explanations CCC: Cause and Effect
Student Experience 6: More of the story (Students hear more of the story from the Mystery at Sunrise Farm Pond and discuss how it relates to their pond models.) 5.LS2.A SEP: Developing and Using Models SEP: Engaging in Argument from Evidence SEP: Asking Questions CCC: Cause and Effect CCC: Systems and System Models