Conceptual Representations
for Learning about Complex
Biological Systems:
From Expertise to Instruction
Cindy E. Hmelo-Silver
Rutgers University
cindy.hmelo-silver@gse.rutgers.edu
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 students
20 Pre-service teachers
13 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
Middle
school
students
Preservice
teachers
Experts
N
Structure
Behavior
Function
20
12.30 (1.17) 6.60 (2.52)
7.60 (3.31)
26
12.15 (1.46) 7.96 (2.20)
7.58 (2.84)
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, mininatural 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
Once this starts you have to
break down the whole aquarium
Toxic waste are nitrogenous
compounds (e.g. ammonia)
going into nitrates
Removes
nitrogenous
wastes
create sores on the fish
and other organisms
Bacteria is a
source of
disease
In nature microbes
utilize waste
produced by animals
Attached to
a stone in a
filter
Permits nitrifying or
denitrifying bacteria to build
up on the charcoal
Mimic natural
environment
FILTER
Cleans water from
organic particles (e.g.
dead tissue)
Absorbed
by the
charcoal
Charcoal
needs to be
charged
Use ladies nylon
stockings to reactivate 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
• Focused on properties
of filter as substrate for
bacterial growth
• Relationship bet pH and
filtration
• No discussion of nittygritty of behavior
• Somewhat abstract
Hobbyist Model of Filter
Keep the
plants happy
Fish like a
current in
the w ater
Keeps the w ater
surface stirred
Necessary for fish
Removes
impurities (e.g.
chlorine)
Filters out particulate
matter like glass w ool
or fiber
Keep the slime
from forming
Pulls the w ater
over a series of
substances
Moves the w ater
several times
gallon/hour
Filters out/
removes
ammonia
and nitrates
If use
carbon
If has Zeloite
in it
charcoal
absorbs gases
• Talk about multiple
functions of filter
• Composition and
mechanics
– ∆ kinds of materials
and their purposes
FILTER
• Connects to other
elements of system
Made of plastic so it
doesn't interact w ith
w ater
Usually run by magnets, spins a
propeller that pulls the w ater in
through the siphon
If w ater level is below
the siphon- it w ill lose
pow er
Pulmonary Physician Model
of Respiratory System
CNS
Carotid body
via chemo
receptors
Angiotensin
Receptors
Chemo
Receptors
Medulla
J receptors
• Looks at system
from many levels
Immune
regulation
controls
Ventral medial
aspect
provides feedback
to the brain by
checking for stretch
Control
checks for oxygen
tension and
regulates
control
controls
controls breathing
rate by checking for
acid-CO2 and H+
has
– CNS and control
check for
oxygenation
• Feedback loops
Heart
Lungs
stimulates/slows
down breathing
depending on
oxygen need
muscles and bones that
control mechanics of
breathing
effects rate
made of
Blood
made of
air comes in/moves
pulls outwards out
carry
help create negative
pressure
include
include
include
Capillaries
terminal
bronchi
pulls downwards
include
carries
close to
end in
goes to
Alveoli
carry blood to
Inter costal
Muscles
Pull them outwards
carried in
Ribs
Oxygen binds to
help pull
Neck and
abdominal
Muscles
bronchi
have
Cells
release oxygen in
and carries CO2
from
Pull downwards
Hemoglobin
O2 goes to
Diaphragm
Trachea
released from
in absence of O2
binds to
released into
Mitochondria
binds to
Carbon
dioxide
create negative
pressure by
working together
this pulls in
carried in air when it
is breathed out
through
Air
produces ATP
through
Larynx,
Pharynx
carried in air that is
breathed through
comes in/ moves out
through
Electron
Transport
chain
Oxygen
ATP used in
Krebs Cycle
Nose
Produce
Energy
RBC
– External Respiration
– Internal Respiration
Respiratory Therapist
Mental Model
Larynx,
phary nx
air passage
Nose
air passage
Trachea
Brain
air passage
controls
Bronchi
work together
controls
controlled by
Diaphragm
moves down to
create negative
pressure
air comes in
through airways
Heart
move outwards to
create negative
pressure and this
pulls in air
Intercostal
muscles
LUNGS
carry oxygenated
blood to
have a network of
capillaries surround
Capillary
work together
carry
protect
Blood
flows nearpumps oxy genated
blood to
Alveoli
Ribs
• Discuss multiple
levels but lungs are
central
• Focus on functions
and behavior that
have direct
implication for
practice
moves out of
Energy
moves into
moves into
moves out of
Carbon
dioxide
Oxy gen
oxy gen used to
provide
carries oxy gen in
RBC
Cells
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
Structure- 27 3.04
centered
(1.01)
Function- 25 3.96
centered
(1.49)*
* p<.05
Invisible
Behaviors
1.00
(1.24)
2.04
(1.69)*
Invisible
Functions
2.07
(1.35)
2.92
(1.58)*
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 12 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 Outcomes
Teacher Time
A
B
Structure
Behavior
Function
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)
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 Inquiry
Teacher 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
For More Information:
cindy.hmelo-silver@gse.rutgers.edu
RepTools software available at:
reptools.rutgers.edu
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