Welcome to the
photosynthesis lab.
In this experiment,
we'll observe
the role of carbon dioxide in
the photosynthesis reactions.
As these photosynthesis
reactions occur,
plants convert carbon
dioxide into carbohydrates--
stored energy we call food.
While oxygen gas is a product
of the light reactions,
carbon dioxide is a reactant
for the Calvin cycle.
We will use live plants
to observe changes
in the concentration of a gas--
carbon dioxide.
Before we begin
filling our test tubes,
let's label them,
number 1 through 5.
First, we will create a
solution, rich in carbon
dioxide, for the experiment.
Using a graduated
cylinder, measure
out 5 milliliters of
bromothymol blue into a small
graduated cylinder.
Add 45 milliliters of water into
the large graduated cylinder.
Take both graduated cylinders,
and pour their contents
into the large beaker,
and swirl to mix.
This is the color of
the bromothymol blue,
with no carbon dioxide added.
Next, we will add carbon dioxide
to the bromothymol blue using
an easily available resource--
our exhaled breath.
Insert the straw,
until it is just
above the bromothymol
blue solution,
but not immersed
in the solution.
Make sure that it does
not touch the liquid.
After taking a deep breath,
gently blow through the straw,
onto the surface of
the bromothymol blue.
Take care to avoid inhaling
the bromothymol blue.
When you see the surface of the
bromothymol blue turn green,
pull out the straw.
Swirl the beaker to
distribute the carbon dioxide.
Once your solution is green,
stop adding carbon dioxide.
If you add too much,
getting a positive result
may take longer than the
scheduled incubation time.
Using a graduated
cylinder, transfer 10
milliliters of the bromothymol
blue solution from the larger
beaker to test tubes
number 1 through 5.
Test tubes 1 through
4 will contain
leaves from your two plants.
These will be your
experimental test tubes.
Test tube 5 will be
used for comparison,
to see how the plants
alter the bromothymol blue.
Now, let's add a leaf
from the aquatic plant,
to test tubes number 1 and 2.
One of your plants needs to be
a water plant, an aquatic plant.
I have elodea
here, or anacharis.
You can get this
at PetSmart, Petco,
in the fish section, any kind of
store that has a fish section.
And you want to cut
off a small sprig.
I can just take it
off with my finger.
And we're going to
place our aquatic plant
into test tube 1 and 2.
And we're going to use the straw
to push it all the way down, so
that it is submerged in the
bromothymol blue solution.
So I'm going to have two sprigs
that I'm going to cut off,
and I'm going to place
them in test tube 1 and 2.
That's going to represent
my aquatic plant.
Now, your second plant type
can be a variety of plants.
It can be plants that--
I picked these off of
bushes outside of my house.
These are spinach leaves
from my vegetable drawer,
and this is just a
common household plant.
As long as you have two healthy
leaves, for test tube 3 and 4,
it should be fine.
I'm going to use these
leaves right here,
and I'm going to pinch
off the entire leaf.
And I'm going to make sure
that my leaf looks healthy.
So for instance,
this one right here,
that's a little destroyed,
I'm not going to use that one.
The leaf, if it's too
big, you can just kind of
fold it up, and kind of bend
it, so that it fits in there.
And then again, use the
straw to push it down
into the bromothymol blue.
And then for additional sources,
you can use your lab manual.
We've created table 1, that
gives you live plant options,
and it gives you
some other sources.
And test tube 5, we're
going to leave it blank.
This is our control, and no
plant is going to be in there.
To determine the effect of
light on photosynthesis,
we're going to take
two test tubes,
and we're going to put
them in a dark environment.
We'll do that by wrapping
the test tube in silver foil.
So we're going to take test
tube number 1 and number 3,
and we're going to
roll it in silver foil,
and we're going to cover the
top to make sure no light comes
through, and the bottom to make
sure no light comes through.
Once you get test tube
number 1 and number 3 wrapped
in aluminum foil, they
are too large to fit
into your test tube rack.
Instead, take one of
your large beakers
from your e-science lab kit,
and place them in there,
so that they are held upright,
and not going to fall over
or fall down.
Test tubes 2, 4, and
5, are now ready to be
placed in direct sunlight.
If it is a cloudy day, we
can also use a desk lamp,
in place of sunlight.
To determine the rate of
carbon dioxide depletion,
record the color in test
tubes number 2 and number 4,
after at least two hours
in direct sunlight,
or a bright desk lamp.
If your bromothymol blue
does not change color
within two hours,
continue your experiment
for an additional hour.
Record your observations
in the column in table 2.
After you observed your
test tubes in the light,
remove the aluminum
foil from test tubes
number 1 and number 3,
and observe the color
of the bromothymol blue.
Record the final color
in the column in table 2.
When making your observations,
compare the color
of the experimental test tube
solution with the control test
tube, number 5.
Once you've completed
your observations,
it's time to clean up.
You can dispose of the
bromothymol blue solution
by pouring it down the
drain, but make sure
you rinse the sink
with plenty of water,
so you don't leave any residue.
When you are done, return
to your online course
to report your results, as
directed by your instructor.
Congratulations, you have just
completed the photosynthesis
lab.
Next time you look at a plant,
think about the importance
of photosynthesis.
See you in the next lab.
