Transcript Analyzing college students’ learning about carbon

Analyzing college students’
learning about carbontransforming processes
Jonathon Schramm, Jennifer Doherty,
and Charles W. Anderson
Michigan State University
Reasoning in college biology
• Typical college biology courses spend a great
deal of time on carbon-transforming processes
(photosynthesis, respiration, carbon cycling, etc).
• Earlier work (Hartley et al. 2011) had shown that many
college students still struggle to apply
scientifically-principled reasoning in their
explanations.
• Current college bio students, both majors and
non-majors, very likely to effect societal policy
positions and stances over coming decades.
Study Design
• Analyzed written pre/post assessments from
1218 biology students in courses taught by 16
different instructors (9 institutions).
• Students randomly assigned assessments built
around one of key carbon-transforming
processes (cellular respiration, photosynthesis, biosynthesis).
• Instructors implemented a variety of
instructional approaches in period between tests.
Summary of General Findings
• College biology students often struggle in similar ways to younger
students with the fundamental reasoning transition from informal
to scientific. Two important differences:
1)
Wealth of terminology & vocabulary available is generally higher
“Which of the following are energy for plants? Water...sunlight...air...soil nutrients?”
College
Although photosynthesis leads to
the production of ATP (energy...
The source of the energy
responsible for all subsequent
reactions comes from the sun
Light is a form of energy while the
non-energy sources are made of
atoms and are considered
matter...bonds between atoms are
chemical energy
Plants need water to help it grow and
blossom, sunlight for energy to make
food, air to help make glucose, nutrients
to help nourish the plant, and plants do
not make their own energy they get it
from sunlight and us it to make glucose.
Plants use sunlight to make their
own energy. Water, air, and
nutrients in soil help the plant
but they do not give the plant
energy because they make their
own using sunlight.
Water and air have stored energy in
chemical bonds, light is a type of
energy. Nutrients do not have stored
energy. Plants use energy to make
their own food.
They all help the plant grow and make
the food (sugar). By using these materials
the plant then photosynthesizes to make
their food and help to multiply their cells
and grow.
Sunlight, helps them with
photosynthesis, nutrients in the
soil help them grow along with
water, and plants are producers.
plants need the light and the nutrients
and the carbon sources to power
photosynthesis to then generate ATP
through the one other cycle
High (L4)
Sun is the only form of energy and
plants convert energy
Med. (L2)
High School
Low (L1)
Middle School
Summary of General Findings
2.
Rates of improvement following targeted instruction tend to be higher
1
0.5
EAP
0
Principles-first Instruction
-0.5
-1
Status quo
instruction
-1.5
-2
Pre
ES
Post
MS
HS
C-T
C-N
Sample Responses – Cell Respiration
When a person loses weight, what happens to the fat in the person’s body? Circle True (T) or False
(F) for each option.
T
T
T
T
F
F
F
F
Some of
Some of
Some of
Some of
the fat is broken down and leaves the person’s body as water and gas.
the fat is converted into energy.
the fat is used up and disappears.
the fat is broken down and leaves the person’s body as feces and urine.
b. Is weight loss connected to anything going on in the person’s cells?
Low (56% of n = 326)
Medium (43%)
High (1%)
T,T,F,T; Fat cells make up
adipose tissue and weight loss
happens when you get less fat
cells
T,T,F,T; The cells go through
cellular respiration. Which is
just the controlled using of
nutrients
T,F,F,F; The fat is not converted
F,T,F,T; Cells need more
glucose, glucogenesis is
initiated to help that need
F,T,F,T; Weight loss has
everything to do w/ the
molecular level...glucose and
triglycerides are broken down
with the use of ATP
into energy, rather the carbonhydrogen and carbon-carbon
bonds are full of potential energy
that is released when they are
broken
T,F,F,F; When a person loses
weight, their body will break the
chemical bonds in the lipids to fuel
cellular respiration, the products of
which are CO2 and water
Results by Process
• College student performance increased on items
about all processes (photosynthesis [PS], cell respiration
EAP
[CR], biosynthesis [BS] and multi-process)
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
BS
CR
Multi
PS
Pre
Post
Original Biosynthesis Items
• Typically asked about organismal growth in a
way that allowed students to emphasize the
energetic requirements, rather than
transformations of matter.
Ex. “the apple provides glucose that the boy’s body
can then use in the Krebs cycle to generate chemical
energy for growth”
• Pointed to a need for more direct way to probe
thinking about biosynthesis.
Revised Biosynthesis Items
• Focus on asking students to identify materials
and/or molecules that are taken in by organisms
and used for growth (i.e. avoid only use in CR)
• Explicitly asking students to explain catabolic
processes.
“How does tree build chemically complex wood from very
simple precursors like glucose?”
• Attempts to connect knowledge about organ
systems to processes happening at molecular scales.
• Administered to 67 students in three introductory biology courses
(post-test only).
Food Chain Similarities & Differences
Grass
Eaten
by
Rabbit
Dies
and
decays
Decomposing
Bacteria
ID specific molecules found in all 3 groups, as well as any
that would be unique to one group.
Commonalities: ‘carbon,’ carbohydrates, lipids, steroids,
DNA/RNA, proteins, ATP, glucose, phosphorus, sulfur, energy
from respiration, H2O
Idiosyncrasies: cellulose, chlorophyll, hemoglobin, energy from
eating thing before it on chain, prokaryote, CO2 in plants, O2 in
animals, methane (bacteria)
Punchline: ~40% (26 of 67) of students noted basic biological
molecules as common to all three forms of life, but only 12% (8
of 67) of students could name even basic unique molecule types
Biosynthesis in Plants (Tree)
Describe how the tree builds wood in its trunk during
growth. How are leaves and roots involved? How
does the tree build the complex molecules of wood
from simpler ones?
Leaves: are sites of photosynthesis, supply energy, supply glucose, act as the
mouth
Roots: take in water, capture nutrients, provide energy sources, act like veins
Complex from simple? through cell division and growth, things brought in
are converted to complex things, uses a combination of materials from
environment, links the monomers taken in into polymers, genes code for
components of wood, molecules are broken down and recombined in various
ways, cell respiration and photosynthesis
Punchline: ~20% (13 of 67) of students describe very general biosynthetic
pathways, while nearly all revert to very general descriptions for role of leaves
and roots in plant growth
Biosynthesis in Humans
Describe how a child grows larger muscles throughout
their body as they grow. How do their digestive and
circulatory systems help? How does the child build the
muscles, and why does a child need so much excess
food during childhood and youth?
Digestion and Circulation: food broken down into simpler
molecules and transported throughout the body; blood transports
O2 to help cells; glycogen is stored in the muscles; release and
absorb ‘nutrients’
How muscles built? by working out/exercising; eating
nutritious food; molecules from food reassembled in fibrous form;
cell growth/mitosis; tearing during training and regrowing;
proteins building more tissue; from production of ATP
Why so much food? extra energy promotes growth; nutrients
to grow larger; adding mass from carbon in CHOs and fats;
burning more ATP; to get vitamins and minerals; cells multiplying
at a higher rate
Implications for Instruction
• Helping students to see the fundamental
connections between PS, BS and CR is crucial:
1) energy is coupled with organic matter during PS,
stays at relatively constant levels during BS and is
decoupled in CR
2) molecules organized
during PS are the basis for
all other molecules in
living organisms, with
some supplementation
from molecules of water
and micronutrients
Alternative Teaching Strategies
• Trace pathways in a more holistic manner
(connect Calvin and Krebs with fatty acids and
secondary metabolites!)
• Especially for intro courses, shift more emphasis
from details to bigger picture (principles) to help
students keep track of the forest
• Incorporate ecological phenomena into cellfocused courses, and vice versa.
Alternative Strategies –
Alternative Responses
An apple is eaten by a boy and digested in his
body. What happens to the apple when it is
digested? Do you think the apple the boy ate
can help parts of his body (like his fingers) to
grow? If so, how does it work?
Traditional L3
Principled L3
Atoms that make up
the apple are broken
down and transfer as
energy into the boys
body
Chemical energy
released can be
transformed into
mechanical energy and
used to build cells
The apple serves as
energy for the body
and energy helps in
growth and
development
The apple is broken
down and used.
Burned to make energy
or used to build carbs,
fats, proteins
Instruction that scaffolds all new
materials around explicit tracing
of matter (atoms) and energy
units transforms student thinking.
(Rice, Doherty and Anderson, reports
forthcoming)