3.8 Inside a photosynthesis lab

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En provenance du cours de Tel Aviv University

Understanding Plants - Part II: Fundamentals of Plant Biology

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Tel Aviv University

Understanding Plants - Part II: Fundamentals of Plant Biology

355 notes

This class is aimed at people interested in understanding the basic science of plant biology. In this four lecture series, we'll first learn about the structure-function of plants and of plant cells. Then we'll try to understand how plants grow and develop, making such complex structures as flowers. Once we know how plants grow and develop, we'll then delve into understanding photosynthesis - how plants take carbon dioxide from the air and water from soil, and turn this into oxygen for us to breathe and sugars for us to eat. In the last lecture we'll learn about the fascinating, important and controversial science behind genetic engineering in agriculture. If you haven't taken it already, you may also be interested in my other course - What A Plant Knows, which examines how plants see, smell, hear and feel their environment: https://www.coursera.org/learn/plantknows. In order to receive academic credit for this course you must successfully pass the academic exam on campus. For information on how to register for the academic exam – https://tauonline.tau.ac.il/registration Additionally, you can apply to certain degrees using the grades you received on the courses. Read more on this here – https://go.tau.ac.il/b.a/mooc-acceptance Teachers interested in teaching this course in their class rooms are invited to explore our Academic High school program here – https://tauonline.tau.ac.il/online-highschool

À partir de la leçon

Photosynthesis

3.1 Chloroplast structure1:30

3.2 Chemical currency: ATP and NADPH4:38

3.3 Light and Photosynthesis3:25

3.4 The light-dependent reactions and electron transfer2:08

3.5 The Light-dependent Reactions and ATP2:16

3.6 Phototsynthesis 2: The dark reactions and sugar synthesis3:50

3.7 Discussion with Prof. Nir Ohad: The Carbon Cycle7:11

3.8 Inside a photosynthesis lab6:15

Rencontrer les enseignants

Professor Daniel Chamovitz, Ph.D.
Dean, George S. Wise Faculty of Life Sciences
Director, Manna Center for Plant Biosciences

So we're now in the laboratory of Dr.

Iftach Yacoby, one of the young researchers at Tel Aviv University.

And as I said Iftach is an expert on photosynthesis.

So Iftach, can you tell us, what are these green things that we have growing here?

>> So the green thing is actually the model system that we are using to study

photosynthesis.

We need a model that can grow fast and is very easy to maintain.

And this model organism is microalgae.

So microalgae is not a bacterium, because it's eukaryotic cells, but

it's unicellular cells.

So unlike higher plants, it doesn't live on terrestrial land.

It lives only in liquid solutions.

You can find them in ponds, sea, you can find them anywhere.

Anything that becomes green suddenly most probably it's microalgae.

The interesting thing about them is that they have photosynthetic machinery,

which is quite similar to those of higher plants.

But unlike higher plants because they grow so fast and so easy to manipulate,

we can do very fast experiments when we have questions about photosynthesis.

>> When we talked about evolution of life on earth and about plants and

about photosynthesis we learned that we started with unicellular organisms.

But is the photosynthesis that goes on in this in this microalgae,

is it essentially the same as in higher plants?

>> It actually is the same in higher plants.

>> So can you show us what type of experiments you do with these organisms?

>> Sure, let's take them upstairs and measure them in our equipment.

>> 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.

One picture equals a thousand words.

>> So here we go from dark to low light to high light,

and you can see how much more photosynthesis is going on.

>> That's correct.

And from that slope,

we can measure exactly what is the rate of the oxygen production.

>> But now, we could actually ask the question,

if I block the flow of electrons, can you still get the oxygen being formed?

>> Let's do that.

>> So now how can we see what would happen if we would stop the electron transport?

>> So that exactly what is going to do.

He's going to inject immediately the inhibitor DCMU that will

block immediately the oxygen production by photosystem two.

So when he injects, the oxygen will go up.

Because we are injecting oxygen from the external space, and

then immediately it will go down.

So you see what's going on.

>> So the lights are still on right now.

>> Yeah, it's still on, you can see that.

>> And even though the light's on, we've stopped electron transport?

>> Immediately.

>> And then no oxygen can be formed anymore.

>> That's correct.

So we have here only respiration now.

>> Only respiration.

So without the electrons, and without electron transport,

the oxygen can't be evolved from the water?

>> That's correct.

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