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Conceptual Representations for Learning about Complex
Biological Systems:From Expertise to Instruction
Cindy E. Hmelo-SilverRutgers University
Overview• Understanding complex systems• Structure-Behavior-Function (SBF) as a
conceptual representation• Expert-novice differences in complex systems
understanding• Conceptual Representations embodied in
instruction– Hypermedia– NetLogo
• Into the classroom
Why Learn about Complex Systems?
• Ubiquitous in the world– Human systems– Cities– Ecosystems
• Important for understanding many aspects of science
• Potential to integrate across disciplines
Understanding Complex Systems
• Difficult because:– Multiple levels of organization that often depend
on local interactions (Wilensky & Resnick, 1999) – Invisible, dynamic phenomena pose barriers to
understanding– Conflict with learners’ prior experience (Feltovich
et al., 2001)– Indirect causality (Perkins & Grotzer, 2000)
Novice Understanding• Focus on the perceptually available structures
(Hmelo, Holton, & Kolodner, 2000; Wood-Robinson, 1995; Hmelo-Silver & Pfeffer, 2004)
• Favor simple explanations, central control (Jacobson, 2001)
• But can conceptual representations provide organizing frameworks for learning about such systems?– Examples: Emergence, Structure-behavior-function
Structure-Behavior-Function (SBF) theory
• Allows effective reasoning about the functional and causal roles played by structural elements in a system (Goel et al., 1996).
• Structures refer to elements of a system• Fish• Filter
• Behaviors refer to how the structures of a system achieve their purpose or output• Filters remove waste by trapping large particles, absorbing chemicals, and converting ammonia into
harmless chemicals
• “Why” Functions refer to why an element exists within a given (designed) system or the output of the system
• The filter removes byproducts from the aquarium
Studying SBF as a conceptual representation
• Expert-novice study
• Two domains:– Aquariums– Human respiratory system
Participants
Respiratory System Interview:
21 Middle school students20 Pre-service teachers13 Experts (8 respiratory
therapists, 5 pulmonary physicians)
Aquarium Interview:
20 Middle School Students
26 Preservice Teachers
9 Experts (5 hobbyists, 4 biologists)
Coding and Analysis
• Interviews were coded according to SBF coding scheme for the presence or absence of a target concept. – Structure
• “There is sand on the bottom” • “The trachea is divided into two parts”
– Behavior• “Fish hide between the plants” • “The brain sends a signal for the diaphragm to contract downward”
– Function • “A filter filters out organic waste”• “Lungs bring air into your body…”
Results: Respiratory System
Sample Responses: What do the lungs do?
• Expert: The lungs, pretty much are the place of oxygen gas exchange. It’s where oxygen comes into the body. It’s where acid load by carbon dioxide is released from the body. That’s its primary function….The tissue lungs…well you have…ACE-inhibitor break down…you have…you also have I think insulin break down. Also that occurs in the lungs too. You have oxygen exchange. That’s primary purpose…lungs are oxygen exchange, well oxygen gas exchange. I’m sorry let me get that correct, gas exchange because you don’t want to leave the carbon dioxide out, which is just as important, and its also a mechanism for managing acidosis, pH balance, because its one of the most quick, it’s the most rapid management. You can blow off CO2 even if the CO2 is normal to maintain a decent pH, so its one of the quick modes of balance, pH balance.
• Pre Service Teacher: The lungs transfer air, transfer oxygen and carbon dioxide I believe back and forth from the blood stream and the air sacs within the lungs in order to provide it to the blood system.
• Middle School Student: Well, they ah, its where the air goes like it helps you breathe. I don’t want to say pumping, but it um, something like that.
Results: Aquarium Systems
N Structure Behavior Function
Middleschoolstudents
20 12.30 (1.17) 6.60 (2.52) 7.60 (3.31)
Pre-serviceteachers
26 12.15 (1.46) 7.96 (2.20) 7.58 (2.84)
Experts 9 13.00 (0.71) 14.89(2.85) 18.56 (4.07)
Sample responses: What do fish do in an aquarium?
• Expert: Hmm. Um, in an aquarium, fish will do many of the same things that they do in their natural life. They’ll forage for food, they will uh, seek mates and attempt to mate. And many times they will successfully reproduce. Um, they eat, they sleep, they burrow for shelter, and they go through a lot of social aggression, interactions, dominance. They establish dominance and attempt to maintain it over other fishes in the tank. Or uh, go in a submissive mode and spend a lot of time hiding from dominant fishes in the tank. …Specifically, you could list a whole bunch of physiological uh, levels of things that fishes do. Like respire, digest, uh grow, um die.
• Pre service teacher: They swim around…they…that’s where they live…so that’s like where their whole habitat is, that’s where there whole life is…
• Middle School Student: They swim around, cause it’s like, their like, mini-natural habitat. Fish always swim in water, so it’s like a converse size of their habitat.
Qualitative Analyses
• Expert interviews:– Provided more elaborate responses – Demonstrated a more integrated understanding that
cut across the SBF levels.
• Novice interviews:– Mentioned numerous structures
Expert-Expert Analyses• All have rich understanding, ∆ emphases
• Biologists/ Pulmonologists tended to have more global, abstract understanding
• Hobbyists/ Respiratory Therapists more local, situated understanding
Biologist Model of Filter
FILTER
Mimic natural
environment
In nature microbes
utilize waste
produced by animals
Toxic waste are nitrogenous
compounds (e.g. ammonia)
going into nitrates
Permits nitrifying or
denitrifying bacteria to build
up on the charcoal
Attached to
a stone in a
filter
Removes
nitrogenous
wastes
Cleans water from
organic particles (e.g.
dead tissue)
Absorbed
by the
charcoal
Charcoal
needs to be
charged
Use ladies nylon
stockings to re-
activate charcoal
PH
maintenance/
adjustment
Put shells in
the filter
Shells are
made
primarily of
calcium
carbonate
Shells buffer PH differences by
taking up excess hydrogen ions and
dissolving or depositing calcium
carbonate into the water
Bacteria is a
source of
disease
create sores on the fish
and other organisms
Once this starts you have to
break down the whole aquarium
• Focused on properties of filter as substrate for bacterial growth
• Relationship bet pH and filtration
• No discussion of nitty-gritty of behavior
• Somewhat abstract
Hobbyist Model of Filter
FILTER
Moves the water
several times
gallon/hour
Necessary for fish
Filters out particulate
matter like glass wool
or fiber
Removes
impurities (e.g.
chlorine)
If has Zeloite
in it
Filters out/
removes
ammonia
and nitrates
Keeps the water
surface stirred
If use
carbon
Fish like a
current in
the water
Pulls the water
over a series of
substances
Keep the slime
from forming
Keep the
plants happy
charcoal
absorbs gases
Made of plastic so it
doesn't interact with
water
Usually run by magnets, spins a
propeller that pulls the water in
through the siphon
If water level is below
the siphon- it will lose
power
• Talk about multiple functions of filter
• Composition and mechanics– ∆ kinds of materials
and their purposes
• Connects to other elements of system
Pulmonary Physician Modelof Respiratory System
has
controls
include
includeinclude
include
Pull downwards
Pull them outwards
help pull
pulls outwards
pulls downwards
provides feedback
to the brain by
checking for stretch
controls breathing
rate by checking for
acid-CO2 and H+
Control
controlscheck for
oxygenation
stimulates/slows
down breathing
depending on
oxygen need
help create negative
pressure
control
effects rate
checks for oxygen
tension and
regulates
air comes in/moves
out
end in
made of
made of
carry
close to
carries
Oxygen binds to
have
carried in
goes to
carry blood to
release oxygen in
and carries CO2
from
O2 goes to
produces ATP
through
ATP used in
Produce
binds to
in absence of O2
binds to
carried in air that is
breathed through
carried in air when it
is breathed out
through
create negative
pressure by
working together
this pulls in
comes in/ moves out
through
released from
released into
CNS
J receptors
Chemo
ReceptorsCarotid body
via chemo
receptors
Blood
Angiotensin
Receptors
Heart
Lungs
Neck and
abdominal
Muscles
muscles and bones that
control mechanics of
breathing
Immune
regulation
Inter costal
Muscles
Ventral medial
aspect
Larynx,
Pharynx
Alveoli
Medulla
terminal
bronchi
Diaphragm
Nose
Trachea
Ribs
bronchi
Capillaries
RBC
Hemoglobin
Cells
Mitochondria
Electron
Transport
chain
Krebs Cycle
Energy
Oxygen
Carbon
dioxide
Air
• Looks at system from many levels– CNS and control
• Feedback loops
– External Respiration– Internal Respiration
Respiratory Therapist Mental Model
air comes in
through airways
air passage
air passage
air passage
controlled by
have a network of
capillaries surround
carry
flows near
moves out of
moves into
moves into
moves out of
carry oxygenated
blood to
pumps oxygenated
blood to
oxygen used to
providecarries oxygen in
controls
controls
moves down to
create negative
pressure
move outwards to
create negative
pressure and this
pulls in air
protect
work together
work together
LUNGS
Capillary
Trachea
Bronchi
Brain
Energy
Alveoli
RBC Cells
Heart
Larynx,
pharynx
Blood
Nose
Intercostal
muscles
Diaphragm
Carbon
dioxide
Oxygen
Ribs
• Discuss multiple levels but lungs are central
• Focus on functions and behavior that have direct implication for practice
Discussion• Visible structures are best understood. • For the experts, behavioral and functional levels are
deep principles that organize their knowledge of the system.
• Although all experts have deep knowledge, there are interesting differences– Biologists/ Physicians think in global and abstract ways. – Hobbyists/ Respiratory therapists think in local and situated
ways.• Raises issue of what are appropriate target models for
instruction
Implications
• The SBF framework may function as a deep principle that maps on to:– expert ways of understanding complex systems – structure of domain.
• SBF framework offers a way for learners to look behind the scenes at phenomena that are not readily perceptually available.
• Organizing learning around deep principles such as SBF might enable students to understand new complex systems they encounter
Conceptual Representations in Hypermedia
• Organizing text and graphics based on:– Expert understanding– Deep principles of domain
• SBF as conceptual representation
• Proof of concept for emphasizing function
Function-centered Hypermedia
Structure-Centered Hypermedia
Comparing Function-centered vs. Structure-centered hypermedia
• Participants: 52 undergraduates enrolled in Educational Psychology– Random assignment to structure- or function- centered condition
respiratory system hypermedia
• Procedure– Students worked with hypermedia x 40 min– Written post-test on respiratory system understanding
• Scoring– SBF coding scheme for the target concepts.
• Structure– “The trachea is divided into two parts”
• Behavior– “The brain sends a signal for the diaphragm to contract downward”
• Function – “Lungs bring air into your body…”
Results: Visible SBF
• Visible SBF includes macrolevel phenomena involved with external respiration– Organ level such as airways, brain, diaphragm, heart, lungs,
muscles, ribs– No significant differences across conditions
Invisible SBF• Includes microlevel structures and phenomena
related to gas exchange, transport, and internal respiration– e.g. alveoli, blood, capillaries, cellular respiration, red blood
cells
• Rarely mentioned by novices in baseline study
N Invisible Structures
Invisible Behaviors
Invisible Functions
Structure -centered
2 7 3.04 (1.01)
1.00 (1.24)
2.07 (1.35)
Function -centered
2 5 3.96 (1.49)*
2.04 (1.69)*
2.92 (1.58)*
* p<.05
RepTools Aquarium Tools
Function-centered Aquarium Hypermedia System
Simulations and Modeling• Allow learners to experience complex systems
phenomena• Simulations and models help focus learners on
function and behavior• Make invisible phenomena visible and open for
inspection• NetLogo as platform for model development
(Wilensky, 1999)– Agent-based modeling tool– High-threshold, low ceiling– Allow understanding of how local interactions contribute to system
behavior
NetLogo Aquarium Model
Nitrification model
In the Classroom• Providing scaffolding and sequencing that
help establish “why” questions• Mix of hands-on activities, hypermedia
resources, simulations, class discussions• Scaffolding needs to encourage mapping:
– Between real world and virtual world– Between different levels– Considering how models simplify the world
Research Context• Goal to support middle school science
instruction in domain of aquarium ecosystem• Units developed with two collaborating
teachers• 145 middle school students in 2 public schools
for about 2 weeks– 70 7th grade with Teacher A– 75 8th grade with Teacher B
• Both classrooms had physical aquaria and 1-2 laptops for each small group
Teaching Contexts• Both teachers experienced, considered
experts• Teacher A
– Used worksheets with open-ended questions– Expected homogeneous progress for whole class– Focus on content
• Teacher B– Inquiry-oriented norms for classroom– Scaffolded exploration by asking students to
observe and explain, open-ended questioning
Research Design
• Pre and post tests of SBF knowledge (Hmelo et al, 2007)
• Comparisons among classroom
• Qualitative analysis of enactments using Interaction Analysis (Jordan & Henderson, 1995)
Learning OutcomesTeacher Time Structure Behavior Function
A Pretest 8.53 (1.68) 4.11 (1.82) 4.50 (2.24)
Posttest* 9.66 (1.17) 5.69 (2.22) 9.13 (2.46)
B Pretest 9.32 (1.10) 4.91 (1.54) 7.10 (2.58)
Posttest* 9.88 (0.97) 7.11 (2.00) 10.53 (3.14)
Enactments
• Although both teachers showed significant gains, IA showed great differences in enactment
• Two areas– Creating opportunities for inquiry– Interpretation of computer models
Creating Opportunities for Inquiry:Teacher A: Adoption of Student Language
• Concentration on definitions of terms• Posed questions requiring one-word response to
class as whole• Questions aimed at reproducing declarative
knowledge• Adoption of student language to convey behavior of
structures• Results suggest student understanding was
scaffolded by connecting to prior knowledge as a way to explain new concepts
Adopting Student Language
• Teacher A: First of all you understand that certain things are living and certain things aren’t. Right? Is ammonia a living creature?
• Class: No!• Teacher A: It doesn’t grow, it doesn’t reproduce, it
doesn’t respond. How do I get more ammonia in the tank?
• Class: Pee• Teacher A: Pee. It’s not like its reproducing and
making more. You want more. You want more, you get more fish and more fish do what?
• Class: Pee!
Creating Opportunities for InquiryTeacher B:
Scientific Terminology and Inquiry Orientation
• Open-ended questions requiring explanations
• Promoted argumentation in student discourse
• Incorporation of new scientific terminology
Scientific Terminology and Process Inquiry
• Alexis: What would happen [if there were no fish]?• Courtney: Well first of all, uh, snails wouldn’t have anything to eat.• Ron: We’re not talking about snails.• Alexis: We’re talking about fish.• Courtney: But they need to have… they wouldn’t make the water dirty. So
then the fish wouldn’t have…• Ron: Alright, so they wouldn’t produce waste. We’re not talking about the
snails.• Alexis: I just think that there would be no point. What are we going to have
a plant farm in water?• Courtney; Basically, nothing would be able to work because the bacteria…• Jenn: Everything lives on fish.• Courtney: The fish produce ammonia, which bacteria makes less harmful
and snails keep the water clean by cleaning the waste and the algae. • Ron: OK, so fish are the basis of all this… ecosystem.
Interpretation of Computer Models:Teacher A: Technology for Instruction
• NetLogo as a teaching aid – Reinforce content knowledge
• Concern with student understanding of computer model as end in itself
• Homogeneous understanding
Technology Use to Provide Instruction
Teacher A: Let’s go over the key. Did you figure out what this is? Class: Yeah.Teacher A: What is it?Class: Plants.Teacher A: Brilliant, that’s a plant, you got that one. [Writes it on board] Did
you get the red dots?Class: Yeah.Teacher A: What’s that?Class: Ammonia.Teacher A: Very good. OK now I’m going to make it a little harder. White
dots?Class: Nitrite.Teacher A: Because what appeared first?Class: Ammonia.Teacher A: Red dots. And what appeared second?Class: White dots.
Interpretation of Computer Models:Teacher B: Technology as a Cognitive Tool
• Technology as cognitive tool– Affords inquiry– Science as a model building activity– Groups notice different aspects of model– Stimulate cognitive engagement
• Use of RepTools to foster deep understanding • Promotion of scientific inquiry• Co-construction of knowledge among group
members
Technology as a Cognitive Tool
Teacher B: …how are you going to know whether the blue boxes are snails, bacteria, what’s the other stuff you said, algae, stuff like that?
Courtney: I don’t think it’s bacteria because the red is ammonia and it’s not eating, it’s not getting rid of it.
Teacher B: How do you know that?Courtney: Because, um well, you can see the ammonia on top of it and it’s
not doing anything to it.Teacher B: Well it’s paused right now.Courtney: Well also because the ammonia is increasing and while these
things are increasing too it’s not decreasing the amount of ammonia. Teacher B: It’s not?Courtney: No, well that’s what I observed. Am I wrong?Teacher B: No, no.Ron: Say that again, Courtney…Courtney: I said, I think that the blue can’t be bacteria because bacteria eats
ammonia and while the blue is increasing the ammonia is still increasing too so if the blue was bacteria…
Discussion• A tale of two classrooms
– Different cultures– Different beliefs about learning and inquiry– Appropriation of tools consistent with beliefs
• Both teachers– Considered expert– Willing to take risks
• Despite differences, similar outcomes – Additional analysis to understand differences
Future Directions• Need to better understand learning processes
– Fine grained analysis of discourse (Liu, 2008)– Effects of teacher guidance (Marathe, in progress)
• More explicit guidance in SBF thinking– ACT (Aquarium Construction Tool) with colleagues
at Georgia Institute of Technology
Challenges for Supporting Learning about Complex Systems
• Cognitive Challenges– Prior knowledge– Developmental level– Reasoning Strategies– Inquiry skills
• Metacognitive Challenges– Planning, monitoring, and evaluating one’s understanding
• Self-regulatory and motivational strategies may be lacking (Azevedo et a., 2005)
• Need for open-ended learning environments WITH scaffolding to help learners deal with complexity
