Hi. It's Mr. Andersen and this
is AP Biology Science Practice 4. It's on
data collection strategies. When I was young
I was inspired by Michael Jordan. So I had
posters of him everywhere. Today I am more
inspired by the academics rather than the
athletic achievements and so this poster might
be on my wall today. We've got the biologists
that jump out, like Darwin, Mendel. Here's
Louis Pasteur. We've got E.O. Wilson and Jane
Goodall. But we also have physicists, chemists
on here. But what ties together all of these
great scientists is their ability to ask questions
and then gather data to answer those questions.
And that's what science is. It's this belief
that we have this objective shared reality.
It's not subjective. It's governed by natural
laws. And then we can discover these natural
laws through observation and experimentation.
A lot of people think that the only thing
scientists do is the scientific method. Now
that's a powerful tool and it's a part of
science, but we also have observational science.
We also have historical science where we look
through the work of others. And we look through
data that was collected through time. And
so it's just one part of it. But when you're
coming up with a controlled experiment, there
are really two parts to that. So let's say
I ask you to develop an inquiry lab where
you're going to measure how the temperature
effects the enzymes activity. And let's say
I frame it a little bit by saying that I want
you to use catalase, which is an enzyme that
breaks down hydrogen peroxide into water and
oxygen. Now this is a lab that we do. We use
chads of filter paper. We dip them in different
concentrations of enzyme and see how long
it takes to float in a beaker filled with
hydrogen peroxide. But if we're changing it
to temperature, now we're going to have to
vary the temperature. So what's our independent
variable? It's going to be the temperature
of the enzyme. And then what's going to be
our dependent variable? Well it's going to
be how fast it acts. And so those first to,
this idea of what are we going to change and
what are we going to measure is only part
of the experiment. The more difficult part
is actually controlling all of the other variables.
We have to make sure, for example, that the
pH stays the same. That the concentration
of the solution stays the same. That we're
getting new hydrogen peroxide each time. And
so in my class I have kids come up with about
ten control variables. And once they do that,
then they're going to be able to collect data
that's pretty valid. So in College Board what
they want you to do is be able to collect
data or understand the collection of data
in each of the four areas. Or the four big
ideas. So in evolution a great example could
be evolution in the stickleback. So the stickleback
fish, remember is a fish found in these glacial
lakes of Alaska. They're quickly adapting
to their local environment. And so we could
measure that by collecting for example, collecting
data on their pelvis length over time. And
as they move from an area where there's a
lot of fish that prey upon them to no fish,
we're going to see quick evolution. If we
look at free energy, it could be data related
to the nutrients cycling. In this case looking
at the amount of nitrogen. If we're looking
at information, we could even go back and
look at historical data. And so Fredrick Griffith
did this famous experiment where he was looking
at different types of bacteria, virulent - nonvirulent,
and then measuring how transformation takes
place. Or if we're looking at systems, we
could be looking at enzymes. And measuring
how lowering that activation energy can increase
the action of the enzymes. And so you have
to be good at understanding how to collect
data. And then see when good data is collected.
And so what kind of questions are you going
to get asked? Well, you're going to get asked
question in four areas. The first one is in
your ability to justify data collection strategies.
And so here is the formula for photosynthesis.
That should jump out to you right away. In
this question they're saying if the input
water is labelled with a radioactive isotope
for oxygen, oxygen 18, then the oxygen gas
released as the reaction proceeds is also
labelled with oxygen 18. Which of the following
is the most likely explanation for that? And
this is a real common type question where
they want to make sure you understand where
all of the atoms are going in that formula.
And so they're going to label one. So which
of the following, this would be like a multiple
choice question, which of the following is
going to be correct? Well let me show you
how I would go at this question. I know that
water is going to be split in the light reaction.
So I immediately could rule out C & D. And
now I have to, I'm kind of down to A & B.
In this one they're saying during the light
reaction hydrogen atoms combine with carbon
dioxide. I know the carbon dioxide doesn't
come in until the Calvin Cycle. And so I would
circle B as the right answer. And so in this
case you're looking at the data that was collected
and then you're justifying the use of that
data. Let's go to the next one. They want
you to be able to design a plan for collecting
data of your own. And so this is an essay
type question that was asked a few years ago.
They're giving you data on the kangaroo rat.
Try to pull yourself away from how cute the
kangaroo rat is to look at the data for a
second. We've got the mean annual precipitation
down on the bottom. And then we have the average
mass on the side. And you can see that there's
an increase in average mass when we have this
kind of a sweet spot here of around 40 millimeters
of annual precipitation. And so they want
you to do two thing. Number one, develop a
hypothesis that would explain the data. And
then number two, design an experiment that
would test the hypothesis. And so the first
part is going to be easy because you can come
up with a lot of ideas. Maybe the parasites
are going to do better at those different
amounts of water. But probably a better guess
is to look at, what is the kangaroo rat eating?
What is it's food supply? And maybe this is
like the perfect food supply. Or in other
words the perfect amount of water for the
food supply, maybe the seeds that are being
produced by grasses to do well. So it doesn't
matter what your hypothesis is. On that first
one you just have to choose one. And after
you've done that we have to design an experiment.
Now when you see design an experiment, I mean
light bulbs should go off. And you could say,
really start thinking about how many points
am I going to get on this essay question.
So I'm going to identify what's my independent
variable, what's my dependent variable. I'm
briefly going to talk about the procedure.
I'm going to talk about statistical analysis
and lots of trials and each of those are going
to get you a point. And so remember you don't
have to do the experiment, you just have to
formulate how you would do the experiment.
And so really shoot for the moon. Let's go
to the next one. You have to be able to collect
data to answer a specific question. And so
in this one this is a practice test. They're
saying that we've got a population of plant
species that are found growing in the mountains.
And then another species that have been found
in the same mountains at lower altitude. So
what they're asking you to do is to describe
two types of data that could be collected
to answer the question, Do these growing above
and below represent a single species? And
so again they're kind of opening it up for
you. And so what would be one thing that starts
for me would be looking, okay what is a species?
How am I going to compare these two? If they
can interbreed and produce fertile offspring,
in other words, I would start pollinating
them, cross-pollinating them and see if I
could produce viable seeds. And so if I can
then that would suggest they're a single species.
Maybe I could start looking at hybrids between
the two groups. Or maybe I could look at the
DNA. That would be another type of data that
I could collect. I could look at the nucleotide
sequences and then see how similar they are
by comparing them. Like using blast analysis.
Or I could look at their chromosome number.
There's lots of ways. And so you really have
to start, this is an open ended question where
you're looking at what kind of data would
I collect? And then finally you have to be
able to evaluate data that they're giving.
And so this is the famous Hershey-Chase experiment.
Remember they were looking at bacteriophages.
Injecting their DNA into bacteria. And so
what they're asking in this essay is why were
radioactive sulfur and phosphorus used in
the Hershey-Chase experiment? And so why are
those great choices? Remember it's because
the phosphorus is dying the phosphate that's
found in the DNA. And we don't have sulfur
in our DNA. Likewise the sulfur is going to
make those, especially disulfide bonds in
the protein, but we're not going to have the
phosphorus inside that. So they were able
to choose properly which atoms they should
use to answer the question that they were
looking at. Which was, what is the transforming
factor? And that's how they discovered that
it was DNA. And so really what makes science
science is our ability to again ask questions
and then gather data. And we have to do that
over and over and over. And a great example
of that would be Mendel. Mendel's ability
to figure out how genetics works just through
experimentation and on peas. Over and over
and over again. And so again, when you get
stuck, look back on that controlled experiment.
What things are required to do that. And I
hope that was helpful.
