>> Iftach, in today's lecture we learned a couple things about photosynthesis.
The first was that photosynthesis in light yields oxygen and
that the amount of oxygen that's produced is dependent on light.
And the second was that once the light hits the photosynthetic
apparatus you get an electron flow.
So can you show us how we actually know this happens using
the machines in your lab?
>> Okay.
So we designed two experiments that we are going to see today.
In the first experiment,
we will see how light intensity affects the yield of oxygen production as you say.
In the second one,
we will use a chemical that specifically blocks photosynthesis two.
And you will see how it costs,
what it does, to the photosynthetic electron current.
And all of that, is only by monitoring the oxygen production.
>> You can monitor actually the oxygen that is produced by these algae?
>> We monitor that in the real time.
>> How do you do that?
>> It's very cool.
So, we have here, a mass spectrometer.
A mass spectrometer is a machine that can, like your nose,
it can smell small gas molecules.
>> [SOUND] >> Yeah, okay.
And we have actually a sniffer here.
It's called a sniffer, and
that sniffer is embedded inside a cuvette that contains those algae.
Now in real time, while we are changing the light intensity,
we can observe how the rate of oxygen depends on that.
If we have a lot of light, we will see a high rate, if we have low light we will
see a low rate, and if we do not have a light at all we will see respiration.
The oxygen won't stay steady.
It will go down because of respiration.
>> And all that in this little thing here?
>> This little thing is combined to all of these huge thing that create
a vacuum that you can find in outer space.
>> Okay. >> That's the amount of vacuum
that we have here.
So I have one of my students that designed the experiment, and
he will show us the experiment.
>> Okay. So Iftach,
can you describe what O'ded's doing as his preparing the experiment?
>> So O'ded is now taking the algae.
He mixes that to make it homogeneous and
then he pours that to fill the cuvette completely.
We can't have any air inside.
>> That's the part that's going to go into the experimental chamber.
>> Now he's inserting the nose,
or the sniffer, we call it, inside the cuvette.
And then we fill that hermetically, so cannot [INAUDIBLE].
>> So the only air that'll be in there is from the oxygen that's
coming from the photosynthesis?
>> So actually we do not have any headspace of gas here.
It's only liquid.
So any gas molecule that is produced immediately is
going into the mass spectrometer.
>> And what about the light?
>> So now he's inserting the light as you can see.
>> Uh-huh.
Is that a very strong light source?
>> Yeah, it can go up to the same intensity as light.
We call it, we measure light in.
>> Intensity of the sun.
>> Sorry? >> Intensity of the sun.
>> Yeah, so in order to honor Albert Einstein, we call it Einstein Unit,
so the intensity of light is microeinstein and sunlight is 2000 microeinsteins.
>> All right, so let me see if I get this correctly.
Here where it's black, that's where it was in the dark?
>> Mm-hm. >> And now we see that there's a little,
the slope is going up a little bit, what does that mean?
>> Because we have a very low light intensity.
>> And so, what's the increase here?
>> We actually see the oxygen accumulation in real time.
>> So each time it's going up, there's more and more and
more oxygen being sensed.
>> Now we switch on the light even higher by intensity.
>> Wow, so now in this really high light intensity,
there's a lot of oxygen being formed.
>> You can see that.