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Hi, my name is Cynthia Sargent,
and I'm the biology curriculum developer and trainer here at PASCO.
And today I would like to share with you our plant respiration and photosynthesis lab.
It's a paper lab that is part of our latest edition of the Biology Through Inquiry manual.
And you can find details at the end of this video for how you can get it as a free download
on our PASCO website.
The lab is designed to help students review the overall process of photosynthesis
and help them relate what they've learned about plant cell structure and the processes of
photosynthesis and respiration to the global carbon cycle.
It's a lab that is easy for students to set up and collect data
in a relatively short period of time.
And it's a good one, giving very consistent results.
Traditionally, labs might be done with Elodea, putting Elodea water with an indicator like
bromothymol blue and waiting 24 hours to see results.
The advantage of this lab is it helps students visualize what's happening directly
to the carbon dioxide levels.
They can see it in a matter of seconds to minutes, they don't have to wait a long time,
and they can see on a graphic display the actual change in carbon dioxide, helping them
relate carbon dioxide directly to the processes of photosynthesis and respiration.
The materials are very simple for the lab.
We're going to use spinach that was just purchased at the grocery store, a Carbon Dioxide Sensor
and the sampling bottle that came along with it, some foil, and a lamp.
So to get started, I already connected my Carbon Dioxide Sensor
to my computer via the SPARKlink.
I'll be using a computer for today's demonstration, but the lab could just as easily be done on
the SPARK Science Learning System.
You'll just be able to view the graph display easier on the laptop computer here.
So my Carbon Dioxide Sensor is already connected to my computer through the extension cable.
And I'm going to calibrate my Carbon Dioxide Sensor before beginning the lab.
So I have a sample of fresh air in the bottle.
I'm just going to plug the bottle with the Carbon Dioxide Sensor.
And there's just a one button calibration for this sensor.
I'm going to hold the green button down for a couple seconds.
There's a green light on the calibration button that will remain static and not blinking
during the time of calibration.
When you see the light begin blinking again, then the calibration is complete.
I have the SPARKvue software open on the laptop computer.
And the page will display the carbon dioxide concentration.
It's not recording any data at this point,
but it will display the carbon dioxide concentration for me.
When calibration is complete, I'll see a number around 400 parts per million.
Now that the calibration is complete, which I know from the light beginning to blink again,
I'm going to remove the Carbon Dioxide Sensor from my sampling bottle.
And I'm going to place one or two spinach leaves into the bottle--it just kind of depends
on the size of your spinach leaves.
I've gently blotted the leaves, so that they're mostly dry.
Ideally we would have the spinach leaves lay flat.
So I'm going to put spinach leaves just through the opening of the bottle.
And I'll go ahead and put a second one in.
I'll lay them flat just to get the maximum amount of surface area
that can be exposed to the light.
I'm going to take a square of aluminum foil, plug my sampling bottle with the spinach leaves
inside with the Carbon Dioxide Sensor.
I'm going to place the sensor and the bottle flat on top of the piece of foil.
And I'll arrange my light.
I've put into the desk lamp here a compact fluorescent light bulb.
And I'll adjust the light so it will shine directly on the leaves within the sampling bottle.
Before I begin data collection, I'm going to need to open up a page or build a page
in the SPARKvue program.
I'm going to choose Build.
My Carbon Dioxide Gas Sensor is listed. I'm going to click on CO2 Concentration.
And I want to create a graph display of that, so I'm going to click on the graph.
But I also am interested in seeing a digits display of carbon dioxide concentration.
So I'm also going to select the number button here and that's going to give me a digits display.
So we'll be able to see a graph and the parts per million in digits as the data is collected.
For this lab, it will take five to ten minutes to collect data.
So I'm going to change the sample rate.
Right now it's 1 Hz.
I'm going to change that to seconds.
And I'm going to have it collect data every two seconds.
If you would like to have the data collection stop at an automatic time,
you can set a stop time, say, three minutes.
Now I'm also going to change my x-axis to read time in minutes instead of seconds.
So I'm going to open up my graph tools.
And I can change the time to minutes instead of seconds.
So I'm now ready to begin data collection.
I'm going to turn on the light, and I'm going to let the light shine directly on the bottle
with the spinach leaves inside for about 30 seconds or so.
The Carbon Dioxide Sensor can be affected by light, and this will allow us to have a
stable reading inside that bottle before beginning to collect data.
When we're ready to collect data,
we're just going to hit the play button to begin data collection.
Now you can see a few data points being collected near the axis of the graph there.
We're going to want to scale the axes to be able to see the greatest view of our change
in carbon dioxide concentration for the bottle.
So I open up the graph tools, and I'm going to choose the scale axis button.
And as the data is collected, the scale of the y-axis will adjust to the new data points.
You can also see in the upper right hand corner a display of the carbon dioxide concentration
in parts per million.
You can see how that is changing as time goes on.
So this lab can be done in two ways.
The students can set it up themselves and work in small teams.
You could also do this lab as a teacher demonstration.
There's a SPARKvue Emulator software that allows you to project this
on to a traditional whiteboard or Smartboard.
As a demonstration, you could be asking the class questions about what they observe
during the time of data collection.
Or if students are working in small teams, you can walk around the classroom and be asking
them questions about what they see on the screen.
So students will probably readily notice the decrease in carbon dioxide concentration
that's occurring in the bottle,
and then you can push them to explain the change that they're seeing and relate that
to the process of photosynthesis that's taking place in the direct light.
For the purposes of our presentation today, I'm going to go ahead and stop data collection
and move on to the second part of the lab.
With the paper lab, if you're following those directions,
the time for data collection would be between five and ten minutes.
To stop data collection, I'm just going to push the button in the lower left corner here,
and you'll see the time stop.
The time was running during the time of data collection, and now the clock has stopped,
showing that my data is no longer being collected.
So now we're going to compare the change in carbon dioxide concentration due to the photosynthesis
and the bright light to what occurs when the plant is in darkness.
So the aluminum foil we'll just fold over the sampling bottle,
so that the leaves will be in complete darkness.
Now you'll notice that I'm going to leave the light on. This will be a controlled variable.
The compact fluorescent light should not provide too much heat to the system, but we'll leave
it on just to control for temperature between the two parts of the investigation.
So now that I've got the bottle sealed in foil so that the leaves are now in complete darkness,
I'll leave my lamp adjusted just as before.
And I'm going to begin data collection again, just by clicking in the lower left side here.
Again you can see the data points being collected on the graph display,
as well as the digits display changing as well.
You can have students predict prior to beginning data collection for run two
what they think will happen when the plant is in darkness.
And then you can ask them as the data is being displayed on the screen whether or not that
matched the prediction that they had in their mind to start with.
So you can see that the Carbon Dioxide Sensor shows a change in carbon dioxide concentration
due to photosynthesis or, in this case, cellular respiration very quickly,
and with a simple setup that is easy for students to perform.
Once data collection is complete,
we can use the graph tools to be able to analyze our data.
Again, for the purposes of today's presentation, we'll stop data collection before the time period
you would traditionally go for in this lab.
So my two runs, you can see, are two different colors.
And there are also different symbols associated with those. You can see a key of those symbols
in this area here.
Right now the Run 2 with the green triangle has a rectangular red box around it.
So that means that that run is the run that's currently selected.
And if I choose my graph analysis tools, that will be the line that is analyzed.
I'm going to go ahead and go back to Run 1 and analyze that one first.
To do that, I'm just going to click on the key for the runs.
And I'm going to click on the symbol for Run 1.
You'll see that moves the rectangle to being around Run 1.
So that's going to allow me to do the analysis with that run.
I'm going to open up my graph tools by selecting the graph icon.
And there are a few things that you can do here.
You can use a statistics tool to get the minimum and the maximum.
So if you want students to look at what the carbon dioxide was at the very beginning
of data collection and at the very end of data collection
and find the change in concentration that occurred during that time period,
the minimum and the maximum is a good tool to use.
You can also use the graph tools to find the rate of the change.
Using this tool, we can do a linear fit.
And you'll see the linear fit gives us the rate of carbon dioxide decrease,
in this case, -66.8 parts per million per minute.
Another tool that we can use, we can use the select feature, the arrow, to be able to select
a part of the line and be able to give that line a label.
So now that I've selected that line, I can open up a text keyboard.
And I can type in an annotation, something like "Direct light".
And I could do the same thing for the darkness.
For that, I would just need to come back to my key for the two runs, select Run 2.
And now that I open up my graph tools, I'll be able to select the Run 2 line
and annotate that just like I did for Run 1.
I'm going to label this one "Darkness".
And I could use the same statistics tools of minimum and maximum to find the change
that occurred during the time period,
or I could also do a linear fit and find the slope and compare the slope for the change
in CO2 in the darkness compared to the rate of change in the light.
So hopefully you've seen from this presentation that providing a lab to your students
that gives them direct evidence of what's happening during photosynthesis and respiration
can be an easy lab to perform.
And one of the reasons I like this lab is not only does it help them understand
those chemical equations for respiration and photosynthesis and the idea of carbon dioxide as a reactant
or product of those processes,
but I also like that this lab lends itself to easy inquiry designed by the students.
So they could use the initial set up and change one variable,
such as the distance of the light to the bottle.
They can also compare different kinds of light bulbs to one another.
So there are many places that students can go in a way that's designed by themselves
to test the effect of a variable on the rate of photosynthesis or cellular respiration.
Thank you for watching our presentation today.
Again, find information at the end of this video
on how you can get the free downloadable paper lab.
And remember to practice safe science.