Hi. It's Mr. Andersen. And welcome to AP Biology Lab 9 walkthrough. This lab
Hi. It's Mr. Andersen. And welcome to AP Biology Lab 9 walkthrough. This lab

is on transpiration. Whenever I hear the word transpiration I immediately think of leaf
is on transpiration. Whenever I hear the word transpiration I immediately think of leaf

evaporation. And so that's the best way to think about it. And you'll have a better understanding
evaporation. And so that's the best way to think about it. And you'll have a better understanding

what transpiration is. Basically what's happening is that water is flowing up a tree. And the
what transpiration is. Basically what's happening is that water is flowing up a tree. And the

way it flows up a tree is the sun. You can see the sun up here is shining. Basically
way it flows up a tree is the sun. You can see the sun up here is shining. Basically

it's heating up the water in the leaf. And the water is evaporating. Now it's leaving
it's heating up the water in the leaf. And the water is evaporating. Now it's leaving

the leaf through something called a stomata. So if this is a cross-section in a leaf, there's
the leaf through something called a stomata. So if this is a cross-section in a leaf, there's

going to be these tiny little holes. Almost like little mouths. They're called stomata.
going to be these tiny little holes. Almost like little mouths. They're called stomata.

And basically water is going to go evaporate out of the stomata. So as it evaporates up
And basically water is going to go evaporate out of the stomata. So as it evaporates up

here, and again the sun is providing the energy, there's going to be a tube that goes all the
here, and again the sun is providing the energy, there's going to be a tube that goes all the

way from here back through the xylem. All the way down the tree. All the way down into
way from here back through the xylem. All the way down the tree. All the way down into

the roots. And so as there's this connected tube of water all the way up to the top. So
the roots. And so as there's this connected tube of water all the way up to the top. So

basically as the water evaporates off the leaf, this whole column is going to move up.
basically as the water evaporates off the leaf, this whole column is going to move up.

Because all of those water molecules are attracted to each other because of hydrogen bonding.
Because all of those water molecules are attracted to each other because of hydrogen bonding.

And so in this lab what we're going to do is measure the rate of that. Now it's hard
And so in this lab what we're going to do is measure the rate of that. Now it's hard

to measure an actual tree so we'll be using something called a potometer. A potometer
to measure an actual tree so we'll be using something called a potometer. A potometer

looks like this. What you do is you take one leaf. And that one leaf is going to be connected
looks like this. What you do is you take one leaf. And that one leaf is going to be connected

to a tube. You have to make sure that it's air tight right here. And then that tube is
to a tube. You have to make sure that it's air tight right here. And then that tube is

going to be filled with water all the way around over to here. So it's basically going
going to be filled with water all the way around over to here. So it's basically going

to line up. And then we're going to have a pipette on this end. So if we zoom in you're
to line up. And then we're going to have a pipette on this end. So if we zoom in you're

going to have pipette that looks just like that. So basically what happens is as water
going to have pipette that looks just like that. So basically what happens is as water

is going to evaporate off of the leaf on this side, that's going to pull water up through
is going to evaporate off of the leaf on this side, that's going to pull water up through

the stem. That's why it has to be air tight here. And as it pull the water like this,
the stem. That's why it has to be air tight here. And as it pull the water like this,

this is going to move that water is going to move down. And so we can measure the rate
this is going to move that water is going to move down. And so we can measure the rate

of that movement. And we can measure the rate of transpiration. Now one thing you have to
of that movement. And we can measure the rate of transpiration. Now one thing you have to

kind of watch out for is that we want to make sure that all leaves are going to be a little
kind of watch out for is that we want to make sure that all leaves are going to be a little

bit different. So one thing you can do is you can put this whole thing on graph paper.
bit different. So one thing you can do is you can put this whole thing on graph paper.

This is really bad graph paper. Like this. And then you can trace the leaf on the graph
This is really bad graph paper. Like this. And then you can trace the leaf on the graph

paper like that. You can calculate the area of the leaf inside it. And so we can make
paper like that. You can calculate the area of the leaf inside it. And so we can make

sure that all leaves are going to be measured as a per surface area. But let me kind of
sure that all leaves are going to be measured as a per surface area. But let me kind of

show you what we have. So this would be our standard lab set up. Basically set up in your
show you what we have. So this would be our standard lab set up. Basically set up in your

lab ready to go. We then compare that over time to the following. We have another one
lab ready to go. We then compare that over time to the following. We have another one

where we put that leaf inside a bag and then we put mist inside the bag. So you may be
where we put that leaf inside a bag and then we put mist inside the bag. So you may be

thinking in the top of your head like, what's going to happen there? Next we have another
thinking in the top of your head like, what's going to happen there? Next we have another

lab set up. We'll call this lab set up three, where we have the leaf in front of a light
lab set up. We'll call this lab set up three, where we have the leaf in front of a light

bulb. Now one important thing that I'm not showing here that you have to have is that
bulb. Now one important thing that I'm not showing here that you have to have is that

you put the light bulb like this. So the light is shining in this direction. We'll also put
you put the light bulb like this. So the light is shining in this direction. We'll also put

some water. And we call that a heat sink. Because we don't want to measure the temperature
some water. And we call that a heat sink. Because we don't want to measure the temperature

and how that effects it. So we'll put a heat sink between the light bulb and then we'll
and how that effects it. So we'll put a heat sink between the light bulb and then we'll

put the leaf over like that. So just the light is moving through. So that would be set up
put the leaf over like that. So just the light is moving through. So that would be set up

three. And then set up four, what we're going to have is a leaf and then a fan blowing on
three. And then set up four, what we're going to have is a leaf and then a fan blowing on

it. And so what you should think in your head is, well how are each of these going to effect
it. And so what you should think in your head is, well how are each of these going to effect

it? And so basically what we find, this is data that was collected in class. So at time
it? And so basically what we find, this is data that was collected in class. So at time

3, 6, 9 all the way through 21 minutes. We should start at 0 as well. What we get is
3, 6, 9 all the way through 21 minutes. We should start at 0 as well. What we get is

a fairly linear relationship. Again this is data that was collected in class. So it's
a fairly linear relationship. Again this is data that was collected in class. So it's

pretty linear. The slope of this line, since we are going over time, the slope of that
pretty linear. The slope of this line, since we are going over time, the slope of that

line, since we're measuring millimeters per meter squared, basically the slop of that
line, since we're measuring millimeters per meter squared, basically the slop of that

line is going to give me the rate. So slope equals the rate. In other words, the steeper
line is going to give me the rate. So slope equals the rate. In other words, the steeper

the slope, the faster the rate. So let me clear all of my scribbling out of the way.
the slope, the faster the rate. So let me clear all of my scribbling out of the way.

Which of these is going to be the fastest? Well the light is going to be the fastest.
Which of these is going to be the fastest? Well the light is going to be the fastest.

Followed by the fan. Followed by the room. Followed by mist. And that's hopefully what
Followed by the fan. Followed by the room. Followed by mist. And that's hopefully what

you were thinking. In other words, if you just think of that leaf like a wet towel that's
you were thinking. In other words, if you just think of that leaf like a wet towel that's

sitting there, what are the following going to do to it? Well in summary, basically if
sitting there, what are the following going to do to it? Well in summary, basically if

you increase the temperature we're going to get an increase in the amount of movement
you increase the temperature we're going to get an increase in the amount of movement

of kinetic energy. And so it's going to increase it. If we increase the humidity, there's going
of kinetic energy. And so it's going to increase it. If we increase the humidity, there's going

to be an indirect relationship. In other words the more humidity we put, the less evaporation.
to be an indirect relationship. In other words the more humidity we put, the less evaporation.

And the reason why is that they simply, the molecules can't jump off and evaporate. If
And the reason why is that they simply, the molecules can't jump off and evaporate. If

we increase air, there's going to be a direct relationship because it's going to move more
we increase air, there's going to be a direct relationship because it's going to move more

of those water molecules away. And light intensity as well. It's going to increase the temperature
of those water molecules away. And light intensity as well. It's going to increase the temperature

of those molecules. It's going to speed up their kinetic energy and they're going to
of those molecules. It's going to speed up their kinetic energy and they're going to

transpire more quickly. And so that's kind of a summary. It's pretty straight forward
transpire more quickly. And so that's kind of a summary. It's pretty straight forward

lab. But I hope that's helpful.
lab. But I hope that's helpful.