C1.3 Photosynthesis [IB Biology SL/HL]

Summary

This script explains the critical role of photosynthesis in energy conversion and food chain formation. It highlights how producers transform light energy into chemical energy, primarily as glucose, using water and carbon dioxide, with oxygen as a byproduct. The script also delves into pigments' role in light absorption, the significance of the oxygen byproduct in Earth's atmosphere, and explores methods to measure photosynthesis rates, including the impact of factors like carbon dioxide concentration, light intensity, and temperature.

Takeaways

• 🌿 Photosynthesis is the process by which producers convert light energy into chemical energy, forming the base of the food chain.
• 🔄 Chemical energy is often in the form of glucose, produced by converting water and carbon dioxide into glucose with oxygen as a byproduct.
• 💧 The oxygen byproduct from photosynthesis is a result of photolysis, where light energy is used to break water molecules.
• 🌱 Producers are essential for both energy conversion and oxygen production, which significantly altered Earth's atmosphere.
• 🌈 Pigments in photosynthetic organisms absorb different wavelengths of light, crucial for the process of photosynthesis.
• 🔬 Chromatography can be used to separate and study different pigments found in plants and algae.
• 📊 The RF value, or retention factor, helps identify pigments by measuring their movement relative to a solvent in chromatography.
• 🌱 Colors are how our brain perceives different wavelengths of light, while pigments absorb and reflect these wavelengths.
• 📈 Chlorophyll, the main pigment in plants, absorbs blue and red light well but not green, which is why it appears green to our eyes.
• 🌡 Limiting factors such as carbon dioxide concentration, temperature, and light intensity can affect the rate of photosynthesis.
• 🌳 Measuring photosynthesis rates can be done through oxygen production or carbon dioxide consumption, with aquatic plants like pondweed being particularly useful for such experiments.

Q & A

What is the primary role of producers in the context of photosynthesis?

Producers, such as plants, are crucial as they can convert light energy into chemical energy, forming the base of the food chain and providing energy that is passed along to consumers.

What is the significance of the chemical energy produced by producers?

The chemical energy produced by producers is essential as it is used to form various biomolecules like carbohydrates, lipids, proteins, and nucleic acids, which are then utilized by other organisms in the food chain.

Why is glucose considered the product of photosynthesis in these examples?

Glucose is highlighted as the product of photosynthesis because it is a simple sugar that serves as a primary source of energy and a building block for more complex carbohydrates.

What is the role of photolysis in photosynthesis?

Photolysis is the process where light energy is used to break apart water molecules into hydrogen ions, electrons, and oxygen gas. The hydrogen is crucial for converting carbon dioxide into glucose.

How did the oxygen byproduct from photosynthesis impact Earth's early atmosphere?

The oxygen byproduct from photosynthesis significantly altered the composition of Earth's atmosphere, leading to substantial changes in the planet's environment and the evolution of life.

What are pigments and how do they relate to photosynthesis?

Pigments are molecules that absorb specific wavelengths of light. In photosynthesis, they are used to absorb light energy, which is then converted into chemical energy.

What is chromatography and how is it used to study pigments?

Chromatography is a process used to separate pigments based on their different solubilities in a solvent. It involves transferring pigments onto chromatography paper and allowing the solvent to move up the paper, separating the pigments.

What is the Retention Factor (RF) value and how is it calculated?

The Retention Factor (RF) value is a ratio calculated by dividing the distance a pigment traveled by the distance the solvent traveled on chromatography paper. It is used to identify different pigments based on their characteristic RF values.

How does the absorption spectrum of chlorophyll relate to the color we perceive in plants?

Chlorophyll appears green to our eyes because it reflects green light while absorbing blue and red light. The absorption spectrum of chlorophyll shows that it is efficient at absorbing blue and red wavelengths but not green, which is why green light is reflected.

What is the difference between an absorption spectrum and an action spectrum for chlorophyll?

While both spectra show the wavelengths chlorophyll can absorb, the absorption spectrum measures the percentage of light absorbed, whereas the action spectrum measures the rate of photosynthesis in response to different wavelengths of light.

How can photosynthesis rates be measured and what are some of the limiting factors?

Photosynthesis rates can be measured through oxygen production or carbon dioxide consumption. Limiting factors include carbon dioxide concentration, light intensity, and temperature, which can affect the rate of photosynthesis until a maximum is reached or the conditions become too extreme.

How can one experimentally manipulate carbon dioxide concentration to study its effect on photosynthesis?

To manipulate carbon dioxide concentration, one can remove CO2 from water by boiling and then reintroduce it by adding sodium hydrogen carbonate. This allows for testing different concentrations to observe their effect on the rate of photosynthesis.

What is a simple method to measure photosynthesis rates using aquatic plants?

One can use aquatic plants like pondweed and count the oxygen bubbles produced during photosynthesis as an indicator of the rate. The number of bubbles correlates with the rate of photosynthesis.

How can leaf discs be used to measure photosynthesis rates?

Leaf discs can be used by observing how quickly they float to the surface of water after photosynthesis begins. As oxygen is produced, the buoyancy of the leaf disc increases, causing it to float, and the time taken to float can indicate the rate of photosynthesis.

What role do pH sensors play in measuring photosynthesis rates?

pH sensors can measure changes in water pH due to the consumption of carbon dioxide by photosynthesizing organisms. As CO2 is consumed, the water becomes less acidic, leading to an increase in pH, which can be correlated with the rate of photosynthesis.

What are Free Air Carbon dioxide Enrichment (FACE) experiments and why are they important?

FACE experiments are conducted on plots of land where carbon dioxide levels are manipulated to study the effects on photosynthesis and ecosystem dynamics. They are important for understanding the potential consequences of increased atmospheric CO2 levels on a larger scale.

Outlines

00:00

🌱 Introduction to Photosynthesis and Energy Conversion

This paragraph introduces photosynthesis as the process of converting light energy into chemical energy, essential for supporting food chains. Producers use water and carbon dioxide to create glucose, with oxygen as a byproduct through a process called photolysis. The importance of photosynthesizing organisms in the evolution of Earth's atmosphere is highlighted, as they played a key role in increasing oxygen levels.

05:01

🌈 Pigments and Chromatography in Photosynthesis

This section explains how photosynthetic organisms absorb light using pigments, which capture different wavelengths of light. Chromatography is used to separate and study pigments. The paragraph details how to calculate the RF value, which is the ratio of the distance traveled by pigments to the distance traveled by the solvent. It emphasizes that pigments absorb and reflect specific wavelengths, influencing their appearance to our eyes.

10:03

🔬 Chlorophyll’s Absorption and Action Spectrum

This paragraph focuses on the absorption spectrum of chlorophyll, explaining that chlorophyll is efficient at absorbing blue and red light, but not green light, which is why plants appear green. The absorption spectrum is compared to the action spectrum, which measures the photosynthetic activity based on absorbed light. Both patterns are similar, but the action spectrum focuses on the rate of photosynthesis under different wavelengths.

15:04

📊 Measuring Photosynthesis Rates and Limiting Factors

Photosynthesis rates can be measured by examining oxygen production or carbon dioxide consumption. Three main limiting factors—carbon dioxide concentration, light intensity, and temperature—affect the rate of photosynthesis. The paragraph explains how enzymes play a role in these processes and describes how changes in these factors can lead to plateaus or sharp declines in photosynthesis efficiency.

20:04

🌿 Investigating Carbon Dioxide and Photosynthesis in Aquatic Plants

This section discusses using aquatic plants like pondweed to measure photosynthesis rates by counting oxygen bubbles. It explains how to manipulate carbon dioxide levels by boiling water to remove CO2 or adding sodium hydrogen carbonate to increase it. The goal is to measure photosynthesis rates at different CO2 levels and identify the optimal concentration where photosynthesis rates plateau.

💡 Light Intensity and Floating Leaf Discs Experiment

The paragraph describes varying light intensity to measure photosynthesis, either by adjusting the light source or using a syringe to remove air from leaf discs. As the leaf discs photosynthesize, they produce oxygen, which makes them float, offering an easy way to measure the photosynthesis rate. The faster the discs float, the higher the rate of photosynthesis.

🔥 Measuring Temperature Effects on Photosynthesis

Temperature’s impact on photosynthesis is examined, with a focus on how enzymes involved in the process are affected by heat. The paragraph explains setting up controlled experiments with water baths to test different temperatures while maintaining consistent levels of light and carbon dioxide. Measuring oxygen production or changes in pH can indicate photosynthesis rates under varying temperatures.

🌍 Large-Scale Carbon Dioxide Experiments and Ecosystem Impact

This paragraph highlights large-scale experiments, such as Free Air Carbon Dioxide Enrichment (FACE), that test the effects of rising atmospheric carbon dioxide on ecosystems. The hypothesis is that increased CO2 levels could boost photosynthesis rates, which may influence plant growth and impact various organisms and abiotic factors within ecosystems.

Keywords

💡Photosynthesis

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigments. It involves the conversion of light energy into chemical energy, which is stored in glucose or other molecules. In the video, photosynthesis is highlighted as the foundational process for energy conversion in ecosystems, with producers like plants capturing light energy and transforming it into chemical energy that feeds the food chain.

💡Energy Conversion

Energy conversion refers to the process of transforming energy from one form to another. In the context of the video, it specifically refers to the conversion of light energy into chemical energy through photosynthesis. This is crucial as it illustrates how producers are able to harness solar energy and convert it into a usable form that can be utilized by other organisms in the ecosystem.

💡Chemical Energy

Chemical energy is the potential energy stored in the bonds of chemical compounds. In the video, chemical energy is produced as a result of photosynthesis, primarily in the form of glucose. This energy is then transferred through the food chain as consumers eat the producers, and it is essential for the sustenance of life.

💡Producers

Producers are organisms that can create their own food from inorganic substances, primarily through the process of photosynthesis. They form the base of the food chain and are vital for the energy flow in ecosystems. The video emphasizes the role of producers in capturing light energy and converting it into chemical energy, which is then available to other organisms.

💡Photolysis

Photolysis is the process of breaking down a compound by the absorption of light. In photosynthesis, photolysis of water molecules is discussed in the video as a critical step where light energy is used to split water into hydrogen ions, electrons, and oxygen gas. This process provides the necessary hydrogen to reduce carbon dioxide into glucose.

💡Pigments

Pigments are substances that absorb light at specific wavelengths and are used by plants to capture light energy for photosynthesis. The video explains that different pigments absorb different wavelengths, and chromatography can be used to separate and study these pigments individually. This is important for understanding how plants utilize various parts of the light spectrum for energy conversion.

💡Chromatography

Chromatography is a laboratory technique used to separate the components of a mixture. In the video, it is mentioned as a method to separate plant pigments, which can then be analyzed for their light absorption properties. This technique is crucial for understanding the different pigments involved in photosynthesis and their roles in capturing light energy.

💡RF Value

The RF (Retention Factor) value is a measure used in chromatography to identify substances based on how far they travel in the solvent front. The video explains calculating the RF value by comparing the distance a pigment travels with the distance the solvent travels. This value is characteristic of different pigments and can be used to identify them.

💡Absorption Spectrum

The absorption spectrum is a graphical representation of the wavelengths of light absorbed by a substance. In the context of the video, the absorption spectrum for chlorophyll is discussed, showing its ability to absorb blue and red light while reflecting green light, which is why chlorophyll appears green to our eyes.

💡Action Spectrum

An action spectrum is a graphical representation that shows the efficiency of different wavelengths of light in supporting a photochemical reaction, such as photosynthesis. The video mentions that the action spectrum for chlorophyll will look similar to its absorption spectrum, but it measures how effectively the absorbed light is used for photosynthesis, not just how much is absorbed.

💡Limiting Factors

Limiting factors are conditions that restrict the rate of a process, such as photosynthesis. The video identifies carbon dioxide concentration, temperature, and light intensity as key limiting factors. Understanding and manipulating these factors are essential for studying and optimizing photosynthesis rates.

Highlights

Photosynthesis is the process of converting light energy into chemical energy, which is vital for the food chain.

Producers convert light energy into chemical energy, passed along to consumers through trophic levels.

Glucose is a product of photosynthesis, formed by combining water and carbon dioxide with oxygen as a byproduct.

Photolysis breaks apart water molecules using light energy to produce hydrogen ions, electrons, and oxygen.

Oxygen production through photosynthesis played a crucial role in the evolution of Earth's atmosphere.

Photosynthetic organisms absorb light using pigments, such as chlorophyll, that capture different wavelengths.

Chromatography is used to separate and identify plant pigments by measuring RF values.

Colors are perceived based on reflected light; pigments absorb and reflect different wavelengths.

Chlorophyll absorbs blue and red light efficiently but reflects green light, which is why plants appear green.

The absorption spectrum shows the specific wavelengths chlorophyll can absorb, while the action spectrum measures the rate of photosynthesis at different wavelengths.

Limiting factors for photosynthesis include carbon dioxide concentration, light intensity, and temperature.

Aquatic plants like pondweed are useful for measuring photosynthesis rates by counting oxygen bubbles produced.

Sodium hydrogen carbonate can be added to increase carbon dioxide levels in aquatic photosynthesis experiments.

Leaf disk flotation is a method to measure photosynthesis rates by tracking the time it takes for leaf disks to float due to oxygen production.

Free Air Carbon Dioxide Enrichment (FACE) experiments investigate the effects of rising carbon dioxide levels on entire ecosystems, potentially increasing photosynthesis rates.

Transcripts

this is the video for all of the

standard level content in C 1.3 on

photosynthesis when we think of

photosynthesis what we really need to

think about is the big picture of energy

conversion and one of the awesome things

that makes producers well awesome is the

fact that they can take light energy and

transform it into chemical energy and

that is just super important because

they form the base of the food chain so

they're again taking light energy and

converting that into chemical energy and

that chemical energy is then passed

along to Consumers and then through

trophic levels and even though a little

bit is lost at each step this initial

transformation of light to chemical is

essential for food chains now that

chemical energy can be in the form of

carbohydrates lipids proteins nucleic

acids all kinds of things now we're

going to focus in on glucose as the

product of photosynthesis in these

examples and to manufacture glucose

producers are going to take water and

carbon dioxide and convert that into

glucose with an oxygen

byproduct why is there an oxygen

byproduct well it comes from this

process called

photolysis photo meaning light Lis

meaning to break we're going to use the

energy from light to break apart water

this water and the reason that we're

doing that is because we need hydrogen

in order to convert this carbon dioxide

into glucose so I'm not going to write

out the balanced um form here but just

so you know photolysis I'm going to be

breaking this into its components so

I'll have hydrogen ions or protons I

will have

electrons okay and I'm going to have

oxygen and that'll be given off in the

form of oxygen gas obviously this isn't

um balanced here but when we think about

this oxygen byproduct it's really from

this photolysis of water okay so we're

using all of these important components

to make glucose and giving this off as a

byproduct and when we think about

evolution of life on Earth especially if

you're studying this course at higher

level um when living things first

started producing this oxygen byproduct

that really changed the composition of

Earth's atmosphere and we saw a lot of

big changes happening after that so not

only are photosynthesizing organisms

very important for energy conversion but

also for oxygen

production now in order for these

photosynthetic organisms to do

photosynthesis they have to be able to

absorb light and they're going to absorb

light using these things called pigments

so pigments are going to absorb

different wavelengths of light and they

actually have many pigments we can

separate those pigments and study them

separately using a process called

chromatography the separation of

pigments you should definitely try this

out on your own here's a quick summary

of how this process would work you would

transfer some pigments from a plant or

algae or something like that onto a

piece of paper so this is called

chromatography paper you allow that

pigment um to come into contact well not

really the pigment but the paper you

allow the paper to come into contact

with some chromatography solvent down at

the bottom something like propen known

so here is my plant pigment that I

transferred and it looks green what's

going to happen is if I let this sit if

I'm patient enough some of this this

solvent will be absorbed by by the paper

and it will start moving up the paper as

it does that okay you can see the after

photo here it's going to separate out

some of the pigments that I transferred

from my plant and so I need two

measurements if I'm going to be able to

identify these pigments I need the

distance that the solvent traveled okay

so how far up the paper did that solvent

go and how far did each of these

pigments go and once I know those two

things I can calculate something called

the RF value okay so the RF value can be

calculated by measuring the distance

that a pigment traveled so let's say my

plant pigment started out here and one

of the pigments I don't know ended up up

here so I would want to measure that

distance and I want to compare that to

the distance that the solvent traveled

so let's say the solvent started down

here and by the end my solvent was up

there so this RF value stands for

retention Factor you don't need to know

that what we do need to know is it's

basically a ratio of the distance

between um or the distance that the

pigment traveled and the solvent

traveled we are going to get different

RF values for different pigments because

different pigments are going to move

different lengths okay okay so some of

them will move um not nearly as far as

the solvent others will move yeah closer

to how far the solvent moved so each

pigment will have a characteristic RF

value and so what that means is that not

only can we separate the pigments but we

can identify the pigments if you're

doing this on your own you can actually

find a table of the known RF values for

different pigments and once you've

calculated yours you can use them to

identify the name of each of these

pigments now colors and pigments aren't

necessarily the same thing colors are

the way that we perceive in our brain

the different wavelengths of light

pigments are going to be things that

absorb and reflect different wavelengths

of light so the pigments that we are

seeing is whatever something else is

reflecting H so what does this mean so

let's say I have a green leaf here okay

so it looks pretty green to me well

what's actually happening and this is my

eye okay I don't know my

eyeball what's actually happening is

that light is bouncing off of this leaf

and we're getting blue light and we're

getting red light and we're getting

green light and we're getting yellow

light so white light is made up of a

mixture of all of these colors this

green plant is going to be absorbed

abing all of these different wavelengths

of light except for the green light and

how do I know it's not absorbing the

green light because it looks green so

what we are perceiving with our eye are

the wavelengths of light that are

reflected by something it is actually

absorbing all of those other colors so

let's take a look at which wavelengths

the pigment chlorophyll is able to

absorb so chlorophyll is the main

pigment in plants and these visible

wavelengths of light run anywhere from

about 400 nanm to 700

nanm these wavelengths of light in the

400 meter range or 400 nanometer range

these are going to be my Blues okay so

like blues and purples and then I'm

going to have greens and I'm going to

have yellows and I'm going going to have

Reds up here in this 700 range now

chlorophyll is very good at absorbing

blue light and really terrible at

absorbing green light and then very good

at absorbing red light and if you look

at an absorption Spectrum for

chlorophyll um like on an internet or in

the textbook you'll see a little bit

more like dips and Peaks and valleys but

in general here is the pattern that you

need to know that chlorophyll is very

good at absorbing blues and reds

terrible at absorbing greens and that is

why to our eye chlorophyll appears green

it's reflecting that light that it does

not absorb and so this is something that

we call chlorophylls absorption Spectrum

it looks like this so that absorption

Spectrum shows us what chlorophyll is

able to absorb in terms of wavelength

that's the absorption Spectrum what

we're going to work on next is something

called an action Spectrum so an action

spectrum is exactly what it sounds like

not only what can it absorb but what can

it do with it so for chlorophyll it's

going to look very similar we're going

to have wavelength and nanometers down

at the bottom ranging from 400 to 700

our visible light spectrum and the

pattern is going to be about the same

okay so the pattern will look very

similar the difference here is what

we're measuring so in an absorption

Spectrum you're measuring what percent

of those lights can chlorophyll absorb

here for the action Spectrum what we're

really looking at is photosynthesis

rates okay so when we say action we mean

what is the plant doing with these

different wavelengths of light and this

is usually expressed as a percent of the

maximum rate of photosynthesis so as you

can see we're getting maximum rates or

close to them um in this 400 nanometer

range and 700 nanometer range but not so

much here in the middle that makes

sense these organisms can do a lot of

photosynthesis when they can absorb a

lot of light and they cannot do a lot of

photosynthesis when they can't absorb

the light now there's a couple of

different ways that you can measure

photosynthesis rates you could look at

oxygen production okay the faster that

oxygen is produced the more

photosynthesis we'll talk more about

these in a minute or you could look at

carbon dioxide consumption but the

important thing to note here is that the

action spectrum and the absorption

Spectrum may look very similar in their

patterns but they are measuring

different things now the next big

learning in this topic is about how we

actually go about measuring

photosynthesis rates and we want to be

able to test the effects of the

different limiting factors on

photosynthesis rates so limiting factors

are exactly what they sound like they

are things that can limit the rate of

photosynthesis and there are three of

them carbon dioxide concentration

temperature and light intensity and

we'll take a look at um all three of

them of course okay so when we're

thinking about carbon dioxide

concentration that's one of the

substrates for photosynthesis so the h

higher the concentration the faster the

rate will be until it reaches a maximum

rate and then it starts to Plateau part

of the reason for that is at some point

all of the enzymes that we need for

photosynthesis will be busy their active

sites will be occupied so there's a

maximum rate there we're going to find a

very similar pattern with light

intensity so we need light for

photolysis and for other things if

you're studying this at HL and so the

more intense the light the faster the

photosynthesis will go until it reaches

a maximum rate and then even if you make

the light brighter and brighter and

brighter the rate will hit a plateau

temperature looks a little bit like this

so as you warm things up things will go

faster and faster and faster and faster

but after a certain point it doesn't

level off it actually drops off quite

sharply and that's due to the fact that

photosynthesis is catalized by n enzymes

and after a certain temperature those

enzymes will start to

denature so we want to be able to

investigate the effects of these

different limiting factors on

photosynthesis so we need to look out

for ways to a measure photosynthesis

rates and B

manipulate um our environment for these

different limiting factors if you have

fancy oxygen sensors or carbon dioxide

sensors then land or terrestrial plants

are great to use if you don't I highly

recommend that you invest in some

aquatic plants because they make

measuring photosynthesis very simple

with relatively little technology so

here we're looking at something called

pondweed pondweed is an aquatic plant

and why is that fun for this well

because plants give off oxygen as a

byproduct and that oxygen is going to be

oxy

gas and oxygen gas when you have it

underwater is going to be in the form of

bubbles so as this plant is

photosynthesizing it's going to get give

off oxygen gas bubbles and you can even

count these oxygen gas bubbles as a way

of measuring the rate of

photosynthesis so now that we know one

way to measure the rate of

photosynthesis let's talk how we might

vary some of those conditions and we'll

work first with the carbon dioxide

concentration so if I want to create uh

again an aquatic environment with no

carbon dioxide then what I would want to

do is boil that water so boil it and

then allow it to cool you don't want to

kill your plant and that boiling is

going to remove the carbon dioxide from

the water so if you're studying

chemistry you know that hot liquids

don't they're not great at dissolving

gases so this is going to remove the

carbon dioxide you can pour it from one

Beaker to the other to oxygenate it

that's fine um and then you can set up

your testing

apparatus when you're doing that okay

counting your oxygen bubbles is a great

way to measure the rate of

photosynthesis you're probably not going

to get a lot of photosynthesis from

water that you've removed the carbon

dioxide from but that's fine that's kind

of like your control group if you want

to then start measuring or adding more

carbon dioxide to your water what you

can do is add sodium hydrogen carbonate

and that will disassociate into carbon

dioxide it'll increase your carbon

dioxide levels so you want to add a

little bit at a time to test different

increments remember what we should be

looking for is this graph like this

where if I have different carbon dioxide

concentrations and I start with zero I

should be getting a photosynthesis rate

of zero but as I go up and up and up I

should see an increased rate until I get

to a certain concentration so what we

want to do is repeat this until the rate

of the bubble production is the same

once we have found that point we have

found this Plateau okay and so this

would then be the optimal concentration

of carbon

dioxide in this next bit we'll kind of

focus on a different way to measure the

photosynthesis photosynthesis rate

because varying the light intensity is

pretty

self-explanatory I would want to have a

light that is either um a higher wated

or something like that or I can move it

closer to or farther away as long as I

have something to mitigate the heat

coming off of that light but anyways

moving that light closer to or farther

away is an easy way to vary light

intensity a cool way to measure this is

to actually use little leaf discs so if

you take a leaf disc so just cut out a

circle from a leaf it's going to have

some air bubbles in it in that spongy

mesophyll layer if you use a syringe to

suck out all of the air bubbles then

when you put it into some water it

should sink to the bottom okay it

doesn't have any air in there it'll

sink as that plant photosynthesizes it's

going to be producing oxygen gas as a

byproduct that oxygen gas is going to

alter the buoyancy of this leaf and it

is going to start to float to the top so

if you time how long it takes for that

leaf disc to float to the top that can

be an indicator of photosynthesis rates

the less time that it takes the faster

your rate of photosynthesis and again I

can vary that light intensity until I

find the point at which varying that

light intensity doesn't result in a

faster rate so to investigate

temperature what you would want to do is

set up your apparatus in a water bath

where you can maybe have a heater or

some kind of heating element that

controls the temperature make sure that

your other limiting factors like light

and carbon dioxide levels are in

abundance that they're not going to

inhibit the photosynthesis in any way so

lots of light lots of sodium hydrogen

carbonate and you can add your culture

of algae or whatever plant you're using

there's a couple of different ways that

you could measure this you could either

um use an oxygen sensor to measure the

oxygen gas that's produced here or and

this is really cool you can actually use

a pH sensor so here's how the pH bit

works as this um organism is

photosynthesizing it is going to consume

carbon dioxide so it will be removing

the carbon dioxide from the water now

carbon dioxide causes water to be more

acidic so if I am removing the carbon

dioxide that means the water is less

acidic and that means I should be

noticing an increase in the pH so the

bigger the increase in PH the higher the

rate of photosynthesis and when I am um

kind of manipulating that temperature I

should notice that as it gets warmer and

warmer and warmer that pH changes more

and more and more until it gets to a

certain point at which time it drops off

due the due to the denaturation of the

enzymes necessary for

photosynthesis now what what do we need

to get out of this well it's important

to understand that we need to pick one

independent variable and make sure that

we control the rest so if you're

choosing carbon dioxide concentrations

you should be thinking sodium hydrogen

carbonate and then controlling light and

temperature again the same for the other

two and you must have a reliable way of

measuring the photosynthesis rates so we

want to have a reliable way of

manipulating and measuring whether

that's counting oxygen bubbles letting

leaves float to the surface using an

oxygen sensor or a pH sensor now we can

really see this play out on a really

large scale in these F Ace free air

carbon dioxide enrichment experiments

and these are very cool so these are

plots of land where certain things have

been controlled um to

investigate potential consequences of

increased carbon dioxide levels so we

think that um this may have an impact on

photosynthesis rates not just in a tiny

little experiment but in ecosystems as a

whole due to the rising carbon dioxide

levels from human activity so the

hypothesis that is that it will actually

increase photosynthesis rates so what

these um people are doing is trying to

control for other factors but

manipulating the amount of carbon

dioxide in the air and measuring things

like plant growth looking at other

limiting factors looking at other parts

of the EOS system like other organisms

and other abiotic factors um so a very

cool connection here to not only

photosynthesis experiments but

interdependence within an ecosystem