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.