eLog7 Photosynthesis

Summary

This educational script delves into the intricacies of photosynthesis, explaining how plants convert light energy into ATP and carbohydrates. It covers the role of chlorophyll, the structure of chloroplasts, and the light-dependent reactions within. The script also explores the Calvin cycle, the process of C3, C4, and CAM photosynthesis, and their adaptations to different environmental conditions, emphasizing the importance of plants in carbon sequestration and oxygen production.

Takeaways

• 🥪 The script starts with a discussion about a sandwich, symbolizing how food is derived from photosynthesis.
• 🌿 Photosynthesis is crucial for understanding where food components like ham, cheese, and wheat come from.
• 🔋 ATP (adenosine triphosphate) is the cellular energy currency, produced through photosynthesis and cellular respiration.
• 🌞 Light energy plays a critical role in photosynthesis, where it's used to convert ADP and inorganic phosphate into ATP.
• 🍃 Chlorophyll and other pigments absorb different wavelengths of light, essential for the photosynthetic process.
• 📍 The chloroplast is the organelle in plant cells where photosynthesis occurs, containing its own DNA.
• 🔄 ATP synthase is a key enzyme that operates in both photosynthesis and cellular respiration, catalyzing the conversion of ADP to ATP.
• 💧 The process of photosynthesis involves the conversion of carbon dioxide and water into glucose and oxygen, facilitated by light energy.
• 🌱 Plants act as carbon sinks, helping to mitigate the greenhouse effect by storing carbon and producing oxygen.
• 🔄 The Calvin cycle is the light-independent reaction of photosynthesis, where carbon dioxide is fixed into glucose using ATP and NADPH.
• 🌱 C3, C4, and CAM photosynthesis are different evolutionary adaptations plants have developed to optimize photosynthesis under various environmental conditions.

Q & A

What is ATP and why is it important in photosynthesis?

ATP, or adenosine triphosphate, is a molecule that provides energy for many cellular processes. In photosynthesis, ATP is produced during the light-dependent reactions and is essential for powering the synthesis of carbohydrates during the Calvin cycle.

How is ATP produced in photosynthesis?

ATP is produced through a process called ATP synthase. Light energy energizes electrons, which move through the electron transport chain, pumping hydrogen ions into the thylakoid. These ions flow back through ATP synthase, causing it to spin and catalyze the production of ATP from ADP and inorganic phosphate.

What is the role of chlorophyll in photosynthesis?

Chlorophyll is the primary pigment responsible for absorbing light energy, which is used to energize electrons during the light-dependent reactions of photosynthesis. Chlorophyll absorbs mostly blue and red light, while reflecting green, which is why plants appear green.

What are the two stages of photosynthesis?

Photosynthesis consists of two stages: light-dependent reactions and the Calvin cycle (light-independent reactions). The light-dependent reactions convert light energy into chemical energy (ATP and NADPH), while the Calvin cycle uses that energy to fix carbon dioxide into glucose.

Why do plants change color in the fall?

Plants change color in the fall because chlorophyll breaks down, revealing other pigments such as beta carotene and xanthophyll. These auxiliary pigments absorb different wavelengths of light and become more visible as chlorophyll is depleted.

What is the function of the electron transport chain in photosynthesis?

The electron transport chain in photosynthesis moves high-energy electrons between protein complexes. As electrons travel through the chain, their energy is used to pump hydrogen ions into the thylakoid, creating a concentration gradient that drives ATP production.

What is the Calvin cycle and what does it produce?

The Calvin cycle is a series of reactions that occur in the stroma of the chloroplast. It uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide into a three-carbon molecule, G3P, which is later used to form glucose.

What is the significance of NADPH in photosynthesis?

NADPH is a high-energy electron carrier produced during the light-dependent reactions of photosynthesis. It provides the reducing power needed to convert carbon dioxide into glucose during the Calvin cycle.

What is C4 photosynthesis and when do plants use it?

C4 photosynthesis is an adaptation for plants in environments with low carbon dioxide concentrations, such as dense plant populations (e.g., cornfields). It spatially separates the light-dependent reactions and the Calvin cycle to optimize carbon dioxide usage and reduce photorespiration.

What is CAM photosynthesis and how does it help plants in dry environments?

CAM photosynthesis is an adaptation that allows plants to survive in dry environments. These plants open their stomata at night to take in carbon dioxide and close them during the day to reduce water loss. The carbon dioxide is stored at night and used during the day for photosynthesis when light is available.

Outlines

00:00

🥪 Discussing a Sandwich and Photosynthesis Connection

The speaker begins by casually enjoying a ham and cheese sandwich, hinting at a deeper topic — photosynthesis. The connection between the sandwich ingredients (lettuce, wheat) and photosynthesis is introduced, stressing the importance of understanding how cellular energy, particularly ATP (adenosine triphosphate), is produced through photosynthesis and its role in creating carbohydrates.

05:00

🌞 ATP Synthase and Photosynthesis Pigments

This paragraph delves into the process of ATP synthesis in photosynthesis, explaining how light energy converts ADP (adenine diphosphate) and inorganic phosphate into ATP. The significance of chlorophyll and other pigments, such as beta-carotene and xanthophyll, is highlighted as the plant absorbs various light wavelengths. The role of chloroplasts, where photosynthesis occurs, is introduced with a focus on the internal structures like the grana and thylakoid membranes.

10:01

🔋 Photosystems and the Electron Transport Chain

The speaker introduces Photosystem II, which absorbs light energy to excite electrons, starting the electron transport chain. Water provides the necessary electrons for this process, resulting in hydrogen ions and oxygen. As these excited electrons move through the electron transport chain, they generate the energy required to pump hydrogen ions into the thylakoid, setting up a concentration gradient crucial for later stages of ATP synthesis.

15:02

⚡ Energizing Electrons in Photosystem I

After electrons pass through Photosystem II, they reach Photosystem I, where they are re-energized by another photon of light. These energized electrons contribute to creating high-energy molecules like NADPH, a vital electron carrier. The movement of hydrogen ions through ATP synthase generates ATP, with the enzyme itself observed spinning during this process. The ATP and NADPH produced are essential for the light-independent reactions of photosynthesis.

20:02

🌿 Calvin Cycle and the Role of Plants in Carbon Storage

The speaker explains the chemical reaction of photosynthesis, where carbon dioxide and water are converted into glucose and oxygen using light energy. This process, crucial for producing food and oxygen, also helps in carbon storage, reducing greenhouse gases. Plants, acting as carbon sinks, are vital in combating global warming. The Calvin Cycle is introduced as the core process of carbon fixation in plants, using ATP and NADPH to convert carbon dioxide into G3P, a precursor to glucose.

🔄 Regenerating RuBP and Energy Use in the Calvin Cycle

Continuing with the Calvin Cycle, the process of regenerating RuBP (ribulose bisphosphate) is described, highlighting the energy expenditure in the form of ATP required for this phase.

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's fundamental to life on Earth as it converts light energy into chemical energy stored in glucose while releasing oxygen as a byproduct. In the script, photosynthesis is discussed in the context of how plants use light energy to make ATP, which is then used to produce carbohydrates like glucose.

💡ATP Synthase

ATP synthase is an enzyme that catalyzes the synthesis of ATP from ADP and inorganic phosphate. It's crucial in energy production within cells. The script mentions ATP synthase in relation to both photosynthesis and cellular respiration, highlighting its role in converting light energy into chemical energy stored in ATP.

💡Chlorophyll

Chlorophyll is a green pigment found in plants that plays a vital role in photosynthesis by absorbing light energy. The script discusses how different types of chlorophyll and auxiliary pigments like beta carotene and xanthophyll are involved in capturing light energy for photosynthesis.

💡Chloroplast

Chloroplasts are the organelles in plant cells that house the photosynthetic pigments and carry out photosynthesis. The script describes the structure of chloroplasts, including their inner and outer membranes, and how they contain their own DNA, supporting the endosymbiotic theory.

💡Granum

A granum is a stack of thylakoid membranes within a chloroplast where the light-dependent reactions of photosynthesis occur. The script uses the analogy of 'stacks of coins' to describe the structure of grana, emphasizing the location of chlorophyll and other pigments.

💡Electron Transport Chain

The electron transport chain is a series of protein complexes that transfer electrons through a series of redox reactions. In the script, it's mentioned as part of the process where light energy is used to energize electrons, which then move through the chain, ultimately leading to the production of ATP.

💡NADPH

NADPH is a high-energy electron carrier molecule that plays a critical role in photosynthesis. The script explains how NADPH is produced during the light-dependent reactions and is later used in the Calvin cycle to fix carbon dioxide into glucose.

💡Calvin Cycle

The Calvin cycle is a set of biochemical reactions that take place in the stroma of chloroplasts, using the energy from ATP and NADPH to fix carbon dioxide into an organic molecule. The script describes how the Calvin cycle operates to produce glucose, a key process in photosynthesis.

💡C3 Photosynthesis

C3 photosynthesis is the most common photosynthetic pathway in plants. The script discusses how it operates under normal conditions, involving the direct use of carbon dioxide in the Calvin cycle.

💡C4 Photosynthesis

C4 photosynthesis is an adaptation in some plants to deal with low carbon dioxide environments. The script explains how it involves a spatial separation of photosynthetic processes, with carbon dioxide being initially fixed into a 4-carbon molecule before entering the Calvin cycle.

💡CAM Photosynthesis

CAM photosynthesis is an adaptation in plants to deal with water scarcity, separating the processes of photosynthesis in time. The script mentions that CAM plants open their stomata at night to take in CO2 and close them during the day to conserve water.

Highlights

The sandwich contains ham, cheese, arugula, and mayo on wheat grit.

Photosynthesis is essential for understanding where our food comes from.

ATP is the cellular energy molecule, synthesized with ATP synthase.

Photosynthesis uses light energy to create ATP from ADP and inorganic phosphate.

Different wavelengths of light are required for photosynthesis.

Chlorophyll and auxiliary pigments like beta carotene and xanthophyll are involved in light absorption.

Chloroplasts, unique to plant cells, contain their own DNA and are the site of photosynthesis.

The granum, a stack of thylakoid membranes, is where light-dependent reactions occur.

The stroma is the site of light-independent reactions, such as the Calvin cycle.

Photosystem II is involved in the initial steps of light-dependent reactions.

Water is split to provide electrons for the electron transport chain in photosynthesis.

The ATP synthase enzyme is likened to a spinning motor, converting ADP and phosphate into ATP.

NADPH is a high-energy electron carrier produced in the light-dependent reactions.

The overall photosynthesis reaction converts CO2 and H2O into glucose and oxygen using light energy.

Plants act as carbon sinks, reducing the greenhouse effect by storing carbon.

The Calvin cycle is the main light-independent reaction that produces glucose from CO2.

C4 photosynthesis is an adaptation to low CO2 environments, involving spatial separation of reactions.

CAM photosynthesis is an adaptation to low water environments, involving temporal separation of reactions.

Stomata are the pores on plant leaves responsible for gas exchange, including water loss through transpiration.

Transcripts

yeah that's

that's a good sandwich

[Music]

it's ham and cheese and arugula mayo

a wheat grit you know this stuff

came do you know where this stuff came

from

it's not the grocery store that's not

the answer

we're gonna find out the next couple

weeks

that's good

all right sandwich eaten it was good

coffee made might be better

so let's get out of here

so it might be kind of weird to talk

about photosynthesis

as where we get our like ham and cheese

um

not so weird to talk about where i got

that like

the lettuce and stuff that we put on our

sandwiches or or maybe even the wheat

but understanding photosynthesis is

super important to understanding

the ham and cheese as well so we got to

start with

cellular energy and that's atp

so atp

which is cellular energy

is made with a molecule called atp

synthase and atp synthase we're going to

talk about

two different times one's in

photosynthesis and once in

cellular respiration so atp synthase

takes

adenine diphosphate

adp plus inorganic phosphate

and we'll represent this with like a p

with a little i

and it turns it into adenine

triphosphate or atp

so photosynthesis is gonna is going to

do this or make atp so that they can

actually make those carbohydrates that

that we've talked about that plants need

and you and i need

okay so photosynthesis is going to use

light energy

to make atp from adenine diphosphate

and inorganic phosphate using atp

synthase

we need like certain kinds of light

energy and then

this picture shows you the different

wavelengths of light now you're going to

see on this picture that's not just

chlorophyll

and that's what you can see outside that

all the leaves as the leaves are

changing colors

we lose all of the green color to the

leaves which is the chlorophyll

different kinds of chlorophyll and what

we're left with are the other

auxiliary pigments like beta carotene or

xanthophyll other the other pigments

that are going to be

used you can see that in this graph

right here okay before we go any farther

we need to understand where this is

taking place the organelle that is in

plant cells that's not in a animal cell

are called chloroplast and chloroplast

where all of the photosynthetic pigments

are located

so you can see in the chloroplast that

there are there's an inner membrane

and an outer membrane and then what we

find is there's the

these membrane kind of like network

inside the chloroplast

and they form these like kind of little

stacks of membranes

similar to maybe what we looked at with

the golgi body maybe a little

and these these stacks this one

stack is called a gran

granum okay um all of them together

plural would be grand

i think you'll hear this a lot said as

like stacks of coins

because they're pretty pretty disc shape

maybe that's different

than the um then the golgi body but this

is where

the chlorophyll and other pigments are

located

and so this is where the all of the

light dependent reactions take place

other interesting aspects about the

chloroplast is that

chloroplasts contain their own dna

this this idea or the

idea that chloroplasts contain their own

dna is

a piece of evidence one of the pieces of

evidence

that link eukaryotes to a

eukaryotes to prokaryotes as this like

the endosymbiotic theory

where at one point we have a ancient

prokaryote eat another prokaryote

and the dna and everything of that

prokaryote that was eaten stays intact

and provides a benefit in this case

energy

to the the the one that ate it another

part that's really going to be important

as we move on uh with regards to parts

of the chloroplast

is going to be the stroma the stroma is

the space

inside the membrane but not

part or outside of the grana

so all of this membrane that makes up

the grana is called

the thylakoid

in here in the picture that you're

looking at

just realize that the stroma that's the

space

inside the membranes of the chloroplast

but outside the thylakoid membrane

um so this is kind of the interior part

and then and then ins that's the top of

the screen and then the bottom of the

screen

is going to be inside the membrane of

the thylakoid so inside a grana

or a granum okay so this is going to be

kind of weird because

what we do is we start with photosystem

so what's kind of weird is we start with

photosystem 2.

photosystem two we start with

photosystem two because it was

discovered after photosystem one

not because it happens first but it was

discovered af um

after photosystem one so what happens is

that we get light

from our environment certain wavelengths

of light

hit photosystem two

and then um you know that you have to

water a plant right

so when we water a plant this is how

we're

providing these electrons for

photosystem 2 and actually this whole

electron transport chain process to work

so we start we can put in some water

and we get out hydrogens

and oxygen atoms

okay so um these elect and then

we drop off the electrons so the light

when it comes down

it energizes these electrons so it

just it doesn't like actually mean that

it moves up inside

um photosystem 2 but just to show that

it moves to a higher

energy state it's

an excited electron okay so

what we see is then that this electron

moves through

the this electron transport chain and as

it moves through the electron transport

chain we have

ion or hydrogen ion pumps so the

hydrogen

ions are going to get pumped through

to the inside of the thylakoid

the energy used to pump these hydrogens

inside the thylakoid

is the high are are the high energy

electrons so this is where we have all

of these hydrogen ions

so we're moving it against the

concentration gradient from high

or we're moving it from low

concentration to high concentration all

right that's going to be important

later so we keep filling this up with

hydrogen ions

all right so when the electrons reach

photosystem one

we're gonna energize them again with

another

photon of light another packet of light

alright so the

the electrons then get re-energized

and this will be important as we get

down down the line

okay so these re-energized electrons

get moved into these

specific proteins to to transfer them

and to react with and

make high-energy electron carriers so

when they get in here these are going to

make

high-energy electron carrier called

n-a-d-p-h

all right we'll talk about that a little

bit more in in a second

all right so here's here is the gist of

this whole thing

okay so we've got all these hydrogen

ions that were built up

and they're going to now move through

the atp synthase from high concentration

we had to pump them in there with using

those high energy electrons

it's going to move through that atp

synthase

and actually what scientists have been

able to like

like image is that this atp synthase is

actually

spinning when it does this which is i

don't know i think kind of interesting

and so we put in as those as that's

spinning right

we put in a dp

and inorganic phosphate

and then what we get out is a

tp all right so the energy used to make

this chemical reaction happen

is the energy from the moving hydrogen

ion

you remember i said we were going to get

back to what happened to the high energy

electrons

after photosystem one well here it is so

what we've got is the

so the high energy electrons

that are re in or the inner the

electrons that are re-energized back to

this higher energy state

from another second photon of light

they are used to make these high energy

electron carriers

and as they move through these proteins

that make this or that

i guess act as enzymes to make this

chemical reaction happen

happen we take n a

d p plus

plus hydrogen and ion

and we use and trap those high energy

electrons

in that in that chemical bond so then

what we get is we have

n a d p

h all right so this is a high energy

electron carrier

okay and this high energy electron

carrier is going to be really important

to the light

independent reactions which we'll talk

about in just a second

i think i may have kind of almost messed

up we didn't even talk about the

um the actual reaction of photosynthesis

so here it is you probably already know

what happens here but let's just

kind of go over it anyways so

photosynthesis

plants take in carbon dioxide

co2 and they react that with water

h2o and then they use

light energy

to to make

glucose c6h12o6

plus oxygen all right so

this is kind of the important part of of

why we need plants

not just for food consumption and not

just

so that we have oxygen to breathe but

what they do is plants big trees

um lots of plants right store

and store carbon as a carbon sink

when we release carbon dioxide out into

the environment

right it's a greenhouse gas part of

global warming

global climate change but if we can trap

the carbon into plants

that carbon isn't affecting the

greenhouse

right so it isn't causing a greenhouse

effect it is not

that carbon is not part of the carbon

dioxide that's causing the greenhouse

effect right the warming causing the

warming of the planet

and the more plants we have the more

oxygen is being produced

so when we um like if we

like a lot of countries or a lot of

places will have like green buildings

where

there's more plant material on the side

or on the roof of the

of the building versus just like making

a concrete structure

um where there is no photosynthesis

going on

any way we can add photosynthesis to our

lives

is going to help trap that carbon

okay so you saw in the light dependent

reactions that's where we use the

water part of the photosynthetic

equation

right in the light independent reaction

is where we're going to use the carbon

dioxide

all right so the light independent

reactions

um there's a lot of reactions the one

like kind of the the main part of this

what we'll call

our what we will say is the main part of

this is called the calvin cycle

this is named after a guy named calvin

they discovered so with the calvin cycle

what we're doing is we're taking our

carbon dioxide and we actually put in

three carbon dioxides into

the calvin cycle so you can see we have

rubp which is a five carbon molecule the

blue dots represent the carbon

and then we take one carbon from one of

the co2 molecules and we add it

to our ubp making it not

making a six carbon molecule now

this is done by rubisco okay so after

this i mean there's a lot of steps and a

lot of enzymes

involved in this and i'm not gonna ask

you to know this but what we have

after we get this six carbon molecule is

that we put in 6 atp

to make some of this stuff happen it

means we get out 6 adp

we put in 6 nadphs and then we get out

6 nadp plus because we've like used up

that electron and the energy in those

bonds so we use these energy molecules

to

make this molecule called g3p

and g3p is a three

carbon molecule that leaves the calvin

cycle

and goes to make glucose all right so

as it continues on really all we're

going to do now is we need to regenerate

our ubp so we have a three carbon

molecule and we're going to add some

more

add some of them together to make

using atp add them together to get our

ubp to regenerate our ubp

so we can make the process right so

this part of where like this is what

we're doing this cycle is going and

going not us

sorry the plants this cycle is going and

going and going

and really all this is doing is making

these three carbon molecules that we're

going to keep stitching

together to make glucose if you remember

the formula for glucose is

c6h12o6

okay so this is all fine and good this

is all fine and good if you have

co2 and water

but what if you don't what if you don't

have what you

need to make what if you don't have what

you need

to make photosynthesis happen so there's

some evolutionary ways that plants have

have developed to deal with this sort of

things

so the normal way plants

photosynthesize is called through a

process called c3 or c3 photosynthesis

so

that's what we just kind of described

and it is kind of what you know of

photosynthesis but

if there's area where there is low

carbon dioxide now it's kind of weird i

just

mentioned that if we don't have plants

then we then we have too much carbon

dioxide in the environment

so what situations would you think of

where there are too many plants

like maybe a corn field right if you

think about the corn

corn plant in the middle of the corn

field the

idea that all of those corn plants are

taking in

carbon dioxide might indicate that there

is a low carbon dioxide environment

there

so they have to have a way to deal with

it and that is called c4

photosynthesis

what part of the photosynthetic process

um

that we've talked about c3

photosynthesis

would need to like have some at

some sort of adaptation if you're in a

low co2 environment

think about it when do we use co2

well we put co2 in in the light

independent reactions

right so that's what c4 photosynthesis

does it has a way to like build up

carbon dioxide before starting the light

independent reactions i just realized i

skipped something else

something about a plant anatomy that

maybe you don't know

um but if we have like if you look at a

leaf on the bottom side of a leaf

typically the bottom side there are

little pores

and i'm not this is not drawn to scale

at all but those pores

or yeah those pores

are called stomata and stomata are super

important this is how all

gas exchange with plants happen so like

we don't think of

plants taking in water because of a gas

exchange but that's exactly how they

take in water

if you water leaves the plant

through the stomata right water leaves

as

water vapor through the stomata and when

it leaves it can suck up more water

through the roots right this is called

transpiration

this process is super important in in

actually the water cycle plants produce

a lot

a lot of water vapor through the process

of transpiration

so c4 photosynthesis separates some of

the processes

in space so there are two different

kinds of cells we have

a mesophyll cell

and then a kind of attached or adjacent

to the mesophyll

cell is another cell called a

a bundle sheath cell

so what happens is that in the mesophyll

cell this is kind of where

co2 is entering from

the stomata and this is where we kind of

go through this process

of c4 photosynthesis so c4

photosynthesis

will actually kind of store and

dump into the bundle sheath

cells extra carbon dioxide

and then it's re then it's kind of

recycled through the same

c3 process so inside the bundle sheath

cells the bundle sheath cells is where

we're going to find

the chloroplast right and this is where

the calvin cycle is going to take place

in c4 photosynthesis calvin cycle is

going to take place in

the bundle sheet cells

so another type of evolutionary

adaptation for plants is called

cam photosynthesis

cam photosynthesis uh let's back up c4

photosynthesis

deals with low carbon dioxide

environments cam photosynthesis

deals with low water environment because

remember those are the two things that

we need to make photosynthesis happen

okay so cam photosynthesis separates

the processes of photosynthesis by time

if you remember c4 separated by space we

had mesophyll and bundle sheet cells

cam photosynthesis separates it by time

so if your stomata if you're a plant and

your stomata are open during the daytime

in a very hot dry place

you're going to lose too much water so

what happens is the

cam plants close the stomata during the

day

and open the stomata at night well this

can pose a problem because

you can't get rid of or you can't take

in co2 and you can't get rid of your

oxygen

when your stomata are closed so what

happens is

at night when the stomata are open they

take in

and store co2 so that during the day

when there is light available then the

light dependent reactions can happen

[Music]

you