Hi. It's Mr. Andersen. Today
I'm going to show you how to do the photosynthesis
lab. It's a really fun lab. But it can be
a little frustrating if you can't get your
leaf chads to sink. And so what you're going
to need is a little bit of distilled water.
So I used 100 milliliters of distilled water.
I need carbon dioxide source. And so we'll
use baking soda. And so what you start with
is 1 gram of baking soda dissolved in 100
milliliters of water. Next we need a leaf.
And so I use these baby spinach. It's organic
spinach that I just buy at a nearby grocery
store. You'll also need a hole punch. And
then you'll need a syringe. And so take the
needle out or it's not going to work real
well. Okay. So the first thing you want to
do is you want to get your leaves. And so
to get your leaves you're going to use your
hole punch. And you're going to punch them
out of the leaf. So you want to try to get
ones that are between the veins. And you can
punch a whole bunch of these out. I'm just
going to do a few. So in one beaker you could
put 20 leaf chads inside there. Next thing
you're going to do, let me show you this.
If I were to take one of these leaf chads
and throw it in water, it's going to float.
So this is our carbon dioxide water. And the
reason it's going to float is that there are
little air pockets within the leaf. And those
make it buoyant. And so what we want to do
in this lab to get started is we want to sink
the chads. And so to do that you're going
to take your chads and you're going to put
them in the syringe. So I took the stopper
out. We're going to load our chads in the
bottom like that. And then we're going to
push that excess air out and push the leaves
to the bottom. Now we're going to grab some
of this carbon dioxide water. We're going
to suck that out like this. And we want to
get rid of all the air at the top. So I'm
getting rid of all the air like that. And
so in here the leaves are still floating.
So you can see that they're at the top of
the syringe. And so our goal is to get them
to sink. And so what we have to do is we have
to pull all of that air out of the leaves
and them replace it with water. And so, I'm
going to get rid of a little water. So to
do that we create a vacuum. And so what I'm
going to do is I'm going to hold my thumb
over the top. And then I'm going to pull on
the bottom. And as I do that I want to shake
the leaves a little bit. And that's going
to keep them in the liquid. So what I'm doing
is I'm pulling that air out of the leaves
and now I'm going to push up, keeping my thumb
on it. And if I do a good job, the leave are
going to start to sink. And so you can see
right now that the leaves are starting to
sink to the bottom. And so now what I've done
is I've taken that air out and then I've replaced
it with water. Okay. So now I want to put
this in my test beaker. And so to do that
I'm going to pull it out the bottom. And they're
going to sink down to the bottom. Now I could
cover this up and keep it in the dark. And
I could get a bunch of the ready to do a number
of trials. But I'm just doing this as a demonstration.
And so the next think I'll do is I'll put
light over the top of it. Now the one think
I should talk about, you can see there's one
leaf chad that still is floating at the top,
is that if I just shine a light like this
it's going to get really really hot in there.
And so that will heat up the water and that's
going to screw up my experiment, what ever
my experiment might be. So you should also
put this over the top. So I'm going to put
this over the top and put a little bit of
just regular water in that. And so what this
will do on the top is it's going to act as
a heat sink. So it's going to absorb the heat
of the light. And so it's just the light that's
actually making its way through. So I'm going
to start it like that. And so things that
you could study, you could study for example
how the concentration of baking soda or concentration
of carbon dioxide effects the light. You could
look at the color of the light. You could
look at different temperatures of the water
inside there. And you could see how all of
those things effect the rate of photosynthesis.
And so what's going to happen next? Well let
me put my phone up and I'm going to start
videoing it. And so let me start the video.
We'll watch the leaf chads. Okay. So what's
going to happen next is that the light is
going to start to provide energy into the
thylakoid membrane of the light reaction.
It's then going to start to split the water
and that's going to create little bubbles
of oxygen. Those bubbles of oxygen are going
to make the leaf chads more buoyant. And eventually
they're going to float to the top. And so
what we're doing is we're measuring the rate
of photosynthesis. You could imagine if I
had more amounts of light that's going to
speed up the rate of photosynthesis. And so
I'll probably have to speed up the video.
It takes a few minutes. Sometimes four or
five minutes depending upon how far the light
is away. But I'll speed it up and you can
check out the leaf chads floating.
