1. Are college students prepared to understand ecosystem carbon cycling?
Why it’s important and how principled reasoning can help.
Laurel Hartley1, Brook Wilke2, Jonathon Schramm3 and Charles W. Anderson3
1Dept. of Biology, University of Colorado, Denver 2Crop and Soil Science, Michigan State University 3Teacher Education, MSU
Introduction
Results
Pre-test
Reasoning about the intersection of social and ecological systems requires an
understanding of the carbon cycle.
We investigated college students’ ability to trace matter and energy through processes that generate, transform and oxidize organic carbon at multiple scales.
Our work builds on current learning progression development for K-12 students’ reasoning about carbon (see other poster in this section; Mohan et al.).
Our work focuses on college student understanding of
Principles: Conservation of Matter and Energy
Processes: Generation, Transformation, and Oxidation of Organic carbon
Scale: Atomic-molecular, Cellular, Organismal, Ecosystem
Carbon-transforming processes are a prominent part of college-level biology curricula, but ideas are typically presented in disconnected ways. We believe that teaching students to explicitly and continuously apply the principles of conservation of matter and energy can lead to a deeper understanding of processes across multiple scales.
Most college student answers were a hybrid of scientific reasoning and informal accounts (Fig. 3).
Students demonstrated similar types of reasoning, both correct and incorrect, across the range of institutions.
Despite the fact that the type & frequency of active instructional interventions used by participating faculty varied, the majority of students saw significant learning gains pre- and post-instruction for both matter- and energy-focused questions (Fig. 3).
Our results both corroborate patterns in student thinking identified in previous studies and lead to further hypotheses about student reasoning (Table 1). A larger range of trends and further questions from this data can be found in our accompanying paper.
Fig. 3. Proportions of students responding with various reasoning strategies for testing on matter and energy before and after instruction. ‘No Data’ primarily means that a student either skipped the question or answered “I don’t know.”
Example Item
Examples
(Informal)
(Scientific)
Trends from Data
For Further Investigation
Matter
Each Spring, farmers plant about 5-10 kg of seed corn per acre for commercial corn production. By the fall, this same acre of corn will yield approximately 4-5 metric tons (4,000 – 5,000 kg) of dry, harvested corn. What percent of the dry biomass of the harvested corn was once in the following substances and locations? Fill in the blanks with approximate percentages; you may use 0% in your response if you feel it is appropriate.
___ % from absorption of mineral substances from the soil via the roots
___ % from absorption of organic substances from the soil via the roots
___ % from incorporation of CO2 gas from the atmosphere into molecules by green leaves
___ % from incorporation of H2O from the soil into molecules by green leaves
___ % from absorption of solar radiation into the leaf
CO2 does add weight but not a lot / as gas and solar energy do not have much mass they do not take up much of the weight
The bulk of the matter ……comes from water absorbed through the roots and carbon dioxide absorbed through the leaves. It also does get a very small amount of potassium, nitrogen, and phosphorus from the soil.
Only 3% (n=40; post: 22%, n=73) of students attributed the bulk of biomass in corn to carbon from the atmosphere, rather than from soil components.
Why do some students think plants get carbon from the soil?
Do students commonly see overly simplified gas-gas and solid-solid cycles?
Do student think atoms can become other atoms?
Why do some students think plants respire and photosynthesize, but only emit O2?
Energy
Consider the three diagrams. They represent three situations in which 100 kg of green plants serve as the original source of food for each of the food chains. In situation II, for example, cattle eat 100 kg of green plants and then people eat the beef that is produced by the cattle as a result of having eaten the plants. In which of the three situations is the most energy available to people?
A) I
B) II
C) III
D) Situations I and II will roughly tie for the
most energy.
E) The same amount of energy will be available
to people in all three situations
A remote island in Lake Superior is uninhabited by humans. The primary mammal populations are white-tailed deer and wolves. The island is left undisturbed for many years. Select the best answer(s) below for what will happen to the average populations of the animals over time.
_____a. On average, there will be more deer than wolves.
_____b. On average, there will more wolves than deer
_____c. On average, the populations of each would be about equal.
_____d. The populations will fluctuate, with sometimes more deer, sometimes more wolves
_____e. None of the above.
Cattle for 100kg provides more calories for less compared to fish and green plants.
[Deer and wolf] populations will fluctuate at times and balance each other out
The sun provides the most energy we use. The plants use the sun so really all energy comes from the sun. Every chain away from the plants is less energy because each animal uses some of the energy provided from the link before them.
Although populations will definitely fluctuate, there will always be more deer than wolves since one wolf must eat many deer over its lifetime to survive.
46% (n=65; post: 74%, n=73) knew that a shorter food chain between producers and humans resulted in more energy for the humans.
89% (n=62; post: 74%, n=73) thought that predator numbers could sustainably be greater than or equal to prey numbers in a closed system.
Do students who can explain how energy and matter are conserved when questions are posed in a standardized way neglect those concepts when questions concern real-world situations or contexts?
Do students think water and nutrients, in addition to sunlight, provide energy for plant growth?
At what scale are students most likely to use energy as a “fudge factor”?
Scale
Once carbon enters a plant, it can …
B) become part of the plant cell walls, protein, fat, and DNA. Circle True or False. Explain
Carbon is essential for life in plants but it isn't found in fat / CO2 could possibly seep into the cell walls of a plant
Then biological processes in the cell turn those simple compounds into all the other compounds that the tree needs to live...proteins, lipids, nucleic acids
60% (n=179; post: 66%, n=91) of students provided no explanation or a vague explanation about how carbon becomes part of the plant.
Do students who can trace matter into and out of an organism often not understand the mechanisms by which matter is used/partitioned once in an organism?
This approach contrasts principled, scientific reasoning with informal or force-dynamic reasoning (Fig. 1).
Objectives:
Look for patterns in student reasoning related to principles, processes, and scales and generate hypotheses for further research.
Examine the effects of instruction on student understanding of carbon related processes.
Fig. 1. Contrasting account frameworks for
reasoning about ecological processes.
Methods
We developed diagnostic question clusters (DQCs) to investigate college students’ reasoning about the carbon cycle. DQCs included 7-10 multiple-choice, true/false and short-answer questions about single processes (e.g. respiration) and multiple processes (e.g respiration and photosynthesis) posed at scales from molecular to ecosystem.
Faculty from 8 institutions (research universities, liberal arts colleges, community colleges) administered 4 DQCs, two focused on carbon cycling and two on energy flow, to students in biology and ecology courses. One carbon and one energy DQC were used as pre tests. Some form of inquiry-based instruction on the topics followed, with details of implementation at the discretion of the faculty. All four DQCs were then administered as post-tests, allowing analysis of differences among students both pre- and post-instruction, as well as between institutions, course types, and pedagogical approaches.
For further details about the DQCs and
particular items, please see our web site at:
At one university, interviews were conducted
to further explore student responses to written questions.
Table 1. A selection of results for each principle from both overall written scores and individual assessments. The last column indicates the type of questions for further study that are emerging from this dataset.
Conclusion
Despite the fact that the principles of matter and energy conservation across multiple scales are fundamental to understanding biology, and particularly ecology, this research indicates that students are not as well-grounded in those principles as faculty often assume. By helping to diagnose this “hidden curriculum” for faculty, DQCs can be an effective tool on which to base further instructional interventions.
Fig. 2. Description of DQC development process.