Hi. It's Mr. Andersen and welcome
to the AP Biology Lab 5 walkthrough. This
is on cellular respiration. And in order to
do that in eukaryotic cells we need this which
is the mitochondria. Basically what goes on
in cellular respiration, I'm not going to
go into too big of depth, but what we're doing
is we're taking a sugar like glucose. And
in the presence of oxygen we're breaking that
down into carbon dioxide and water. We're
producing energy in the form of ATP. Remember
there are three different steps. We have glycolysis
which is going to occur outside of the mitochondria.
We have the Krebs cycle with occurs inside
the mitochondria. We're going to give off
carbon dioxide. And we're going to produce
NADH and FADH. And then finally we have the
electron transport chain. Where we're going
to use the energy in NADH and FADH to make
ATP. Or to generate ATP. But in this lab what
we're really trying to do is measure the rate
of respiration. The rate of cellular respiration.
And we do that by measuring the rate at which
oxygen is being consumed. And so in this lab
set up we're going to use two different things.
We're going to use worms. And then we're going
to use peas. Now you might think peas, well
they don't respire. Of course they do. In
other words plants grow and they use photosynthesis
to produce sugars. But then they breakdown
that sugar to produce ATP and energy. And
they're doing that so they can grow. And so
since this pea is going to be underneath the
soil, it need energy to grow. And it can do
that through cellular respiration. Okay. So
what do we use to measure this? We're using
something called a respirometer. Respirometer
has important parts to it. It's got a glass
jar here on the bottom. Usually I'll put weights
on the bottom so it's going to sink. And I'll
get to that in just a second. On the bottom
we're going to have some cotton. And that
cotton is going to have this chemical in it.
It's called potassium hydroxide. Potassium
hydroxide will be a the bottom of in this
absorbent cotton down at the bottom. Basically
what potassium hydroxide does is if it ever
in the presence of carbon dioxide, it will
convert that into a solid. In other words
if we were to put peas inside here they would
take in oxygen. But they would produce an
equal amount of carbon dioxide. And so that
volume wouldn't change in here. But since
we have the potassium hydroxide it's going
to convert any carbon dioxide that's produced
into this solid. So we really don't have to
worry about its volume. Some other things
that we'll use in this lab. We'll use beads
to make sure that we can account for temperature
changes or fluctuations. And also to keep
the volume the same. And then we'll use an
equilibration period. So basically how do
you build it? At the bottom you're going to
put some KOH. A little bit of cotton. Then
you're going to put your pea seeds over the
top of it. And you're going to seal it. And
we're going to have a little pipette like
this. Now the three different types that AP
suggests, oops let me go back for just a second.
Okay. Now the three jars that AP suggests
that we're going to have one where we're going
to have peas in it. We're going to have one
where we have dry peas or non germinating
peas. And then we're going to have one where
we're going to use just glass beads. Now these
glass beads are simply a control. These ones
are used to subtract our values to account
for fluctuations in the temperature and how
that effects it. So what we're really comparing
is we've got germinating peas. We've got non-germinating
peas. And then we've got worms. And so we're
not really going to concern ourself with this.
We use it to correct our values. But we're
looking at the respiration rate of worms,
germinating peas, non germinating peas and
see how that changes over time. So let's look
at what happens. We take our respirometer.
We're going to put it under water. We're going
to let it set and equilibrate. And basically
what you'll get is a little air bubble that
forms right here. So there's going to be oxygen
inside here. Oxygen is going to go all the
way out here. And then water is going to start
to creep in over here. So now we let it sit.
So I start at 0 and then 5 and then 10 and
then 15 minutes. And basically what is going
to happen is that pea is going to start to
consume oxygen. It's going to produce carbon
dioxide. But remember that carbon dioxide
will build up as a solid down here in the
bottom. So you don't have to worry about it.
We're going to decrease the amount of volume
inside the respirometer. And then the water
pressure is going to start to move this bubble
farther and farther and farther in. And so
we can measure the rate at which this bubble
flows in. And that's going to be the rate
of respiration. It's kind of hard to read
this under water because you eye is going
to be right up here at that top. So you got
to get used to that. But it's a really simple
elegant experiment that we can use to measure
respiration. What do we find? Well here's
some data. So here would be the beads alone.
Again we're using that to just accommodate
for any changes. Because temperature fluctuations
are going to have a huge influence on this.
We now got our germinating peas, dry peas
and then worms. And so we can subtract any
changes inside the beads from these other
ones to account for any changes in temperature.
But if you look at this person's data, what
they got is the steepest line and these should
all be linear, is going to be the germinating
peas. So the germinating peas are going to
have a line like that. So this is the milliliters
of oxygen consumed. Then it's going to be
time on the bottom. So time in minutes. And
so the slope of this line, if I were to figure
out the slope of this line, in milliliters
oxygen consumed over minutes, that's going
to be the rate of respiration. We'll find
that that's a greater rate than that of the
worm. And a greater rate than that of the
non germinating peas. And that's because these
ones are not activated. They're not doing
cellular respiration. If we were to soak them
in water, then they would start to actually
do those things. And so we could do the rate
of each of those. Then graph it. And that
would be a histogram of the rate or the change
over time. And so that's the respiration lab
and I hope that's helpful.
