Photosynthesis (in detail)

Summary

The video delves into the intricate process of photosynthesis, breaking it down into two main stages: light-dependent and light-independent reactions. It explains how sunlight powers photosynthesis, converting water and carbon dioxide into oxygen and glucose. Visible light, especially blue and red wavelengths, drives this process, while green light is mostly reflected. The video highlights key structures like chloroplasts, thylakoids, and stomata, alongside crucial molecules such as ATP, NADPH, and glucose. It also touches on autotrophs beyond plants, including algae and cyanobacteria, emphasizing their role in photosynthesis.

Takeaways

• 🌞 Photosynthesis is a complex process that converts sunlight into glucose and oxygen, utilizing carbon dioxide and water.
• 🌈 Sunlight, also called white light, consists of a spectrum of colors (ROYGBIV), and these different wavelengths play a key role in photosynthesis.
• 🍃 Plants appear green because they reflect green light while absorbing other colors, particularly red and blue wavelengths, which are most effective for photosynthesis.
• 📊 Photosynthesis involves two main stages: light-dependent reactions (occur in the thylakoid membranes) and light-independent reactions (occur in the stroma of chloroplasts).
• 🔋 During the light-dependent reactions, sunlight excites electrons in chlorophyll, which initiates the electron transport chain and produces ATP and NADPH.
• 💧 Water molecules are split during the light-dependent reactions, providing replacement electrons for chlorophyll and releasing oxygen as a byproduct.
• 🔄 The Calvin cycle (light-independent reactions) utilizes ATP, NADPH, and carbon dioxide to produce simple sugars like glucose.
• 🌀 Rubisco is involved in bonding carbon dioxide with RuBP, forming a short-lived six-carbon molecule, which is then broken down into two three-carbon molecules (PGA).
• 🛠 Some of the produced molecules (PGA) help create glucose, while others regenerate RuBP, allowing the Calvin cycle to continue.
• 🌱 Autotrophs, including plants, algae, and cyanobacteria, perform photosynthesis to convert solar energy into chemical energy.

Q & A

What is the primary role of sunlight in photosynthesis?

Sunlight provides the energy required to power photosynthesis, specifically through the absorption of visible light by chlorophyll in the plant's chloroplasts.

How does the color of an object affect the light it reflects and absorbs?

The color of an object is determined by the wavelengths of light it reflects. For example, a green leaf reflects green light and absorbs other colors, while a white object reflects all colors of light.

What is the significance of the wavelengths of light around 400 nanometers and 700 nanometers in photosynthesis?

The wavelengths around 400 nanometers (blue light) and 700 nanometers (red light) are most stimulating for plants during photosynthesis, as they are absorbed most effectively by chlorophyll.

Why do plants appear green if they absorb the most blue and red light?

Plants appear green because they reflect the green wavelength of light while absorbing other colors. The green light has the least impact on photosynthesis because it is mostly reflected rather than absorbed.

What are the reactants and products of photosynthesis?

In photosynthesis, carbon dioxide and water are the reactants, and with the presence of sunlight, they produce glucose and oxygen.

What is the role of stomata in the process of photosynthesis?

Stomata are pores on the underside of leaves that facilitate gas exchange. They allow plants to take in carbon dioxide from the atmosphere and release oxygen as a waste product.

What are the two stages of photosynthesis and where do they occur?

Photosynthesis is divided into two stages: the light-dependent reactions, which occur in the thylakoid membranes of the chloroplast, and the light-independent reactions, also known as the Calvin cycle, which occur in the stroma of the chloroplast.

What are the photosystems and where are they located?

Photosystems, named Photosystem I and Photosystem II, are located in the thylakoid membranes of the chloroplast. They contain chlorophyll and are responsible for capturing and transferring energy during the light-dependent reactions.

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

The electron transport chain is a series of events initiated by electrons from chlorophyll that flow through the thylakoid membrane, creating a negatively charged environment and leading to the production of ATP and NADPH.

How is oxygen produced during the process of photosynthesis?

Oxygen is produced as a byproduct when water molecules are split to provide electrons to Photosystem II, releasing oxygen atoms that bond together to form molecular oxygen (O2).

What is the Calvin cycle and what is its role in photosynthesis?

The Calvin cycle is the light-independent reaction phase of photosynthesis where carbon dioxide is fixed into an organic molecule using the energy from ATP and NADPH, ultimately producing glucose.

Outlines

00:00

🌞 Introduction to Photosynthesis and Light Energy

The video begins with a basic introduction to photosynthesis, explaining how sunlight, water, and carbon dioxide contribute to the production of oxygen and glucose in plants. However, the process is much more complex than it seems. Visible light, a component of the Sun's energy, plays a key role in photosynthesis. The concept of white light, made of different colors (ROYGBIV), is explained using a prism, which shows how white light separates into different wavelengths. The absorption and reflection of light by objects, like leaves reflecting green light, is also discussed in relation to photosynthesis.

05:01

🍃 Light and Color in Photosynthesis

This paragraph explores how colors are either reflected or absorbed when sunlight strikes an object. For example, green leaves reflect green light, while other colors are absorbed to power photosynthesis. The graph discussed shows how blue and red light are most effective for photosynthesis, while green light, though associated with plant color, has the least impact. The definition of photosynthesis is provided, along with its formula: carbon dioxide and water, in the presence of sunlight, produce glucose and oxygen. The section also introduces various autotrophs like algae, kelp, and cyanobacteria that perform photosynthesis.

10:01

🔋 Endergonic Reactions and Stomata

The concept of photosynthesis as an endergonic reaction is introduced, requiring energy input from sunlight. The products, oxygen, and glucose, are mentioned along with the role of stomata—tiny pores on the underside of leaves that allow the exchange of gases like carbon dioxide and oxygen with the atmosphere. This section also introduces the chloroplast, the organelle where photosynthesis occurs, and breaks the process into two stages: light-dependent reactions and light-independent reactions. The thylakoid membranes in the chloroplast and their role in the light-dependent reactions are also discussed.

15:01

🌿 Light Dependent Reactions and Photosystems

This paragraph dives deeper into the light-dependent reactions, starting with photosystem II absorbing sunlight. Chlorophyll molecules become excited and initiate an electron transport chain within the thylakoid membrane. Water molecules are broken apart, replenishing the electrons in photosystem II and producing oxygen as a byproduct. Photosystem I is also involved, absorbing sunlight and continuing the electron transport chain. This process eventually leads to the creation of NADPH, a molecule important for transferring hydrogen, and a buildup of hydrogen ions in the thylakoid, which will later be used to produce ATP.

⚛️ ATP and NADPH Formation in Light Dependent Reactions

This section explains how the accumulation of hydrogen ions inside the thylakoid helps create ATP through ATP synthase. The movement of hydrogen ions from high to low concentration through this enzyme facilitates the bonding of ADP and phosphate to form ATP. At this point, NADPH and ATP are the primary products of the light-dependent reactions, and no glucose has been formed yet. The summary of this stage highlights the creation of oxygen, NADPH, and ATP using sunlight and water, setting the stage for the light-independent reactions.

🌱 The Calvin Cycle and Glucose Production

The Calvin Cycle, also known as the light-independent reactions, is introduced. It starts with the five-carbon molecule ribulose bisphosphate (RuBP) bonding with carbon dioxide to form a short-lived six-carbon molecule. This molecule is broken down with the help of ATP and NADPH, resulting in two three-carbon molecules called phosphoglycerate (PGA). Some of these PGAs are then used to form glucose, while others help regenerate RuBP, allowing the cycle to continue. The paragraph emphasizes the use of energy from ATP and NADPH, created in the light-dependent reactions, to drive this process.

🌀 Recap of the Calvin Cycle and Energy Flow

The final paragraph summarizes the Calvin Cycle, noting that carbon dioxide, ATP, and NADPH are essential for creating glucose. The cycle continuously regenerates RuBP, allowing the process to repeat. This section reinforces that the light-dependent reactions produce the ATP and NADPH required for the light-independent reactions, ultimately resulting in glucose production. The video wraps up with a call for viewers to answer related questions, signaling the end of the discussion on photosynthesis.

Keywords

💡Photosynthesis

Photosynthesis is the process by which plants and other autotrophs convert solar energy into chemical energy in the form of glucose. In the video, it is explained as a complex process involving the absorption of sunlight and its use in creating sugars and oxygen, which plants release into the atmosphere.

💡Chlorophyll

Chlorophyll is the green pigment found in plants that absorbs sunlight, facilitating the process of photosynthesis. The video highlights how chlorophyll in photosystems captures sunlight to energize electrons, which is a critical part of the light-dependent reactions.

💡Thylakoid

Thylakoids are membrane-bound structures within chloroplasts where the light-dependent reactions of photosynthesis take place. They are described in the video as coin-like stacks where sunlight is absorbed and converted into chemical energy, producing ATP and NADPH.

💡Light-dependent reactions

Light-dependent reactions are the first stage of photosynthesis, occurring in the thylakoid membranes. These reactions require sunlight to generate ATP, NADPH, and oxygen. The video explains how sunlight excites electrons in chlorophyll, driving the production of energy molecules needed for the next phase.

💡Calvin cycle

The Calvin cycle, or light-independent reactions, is the second stage of photosynthesis where ATP and NADPH produced in the light-dependent reactions are used to fix carbon dioxide and create glucose. The video describes how carbon dioxide is incorporated into a cycle of reactions, resulting in the formation of sugars like glucose.

💡Autotrophs

Autotrophs are organisms that produce their own food through processes like photosynthesis. While plants are the most commonly known autotrophs, the video also mentions algae, phytoplankton, and cyanobacteria as other examples of autotrophic organisms.

💡Electron transport chain

The electron transport chain refers to the series of protein complexes in the thylakoid membrane that transfer electrons during the light-dependent reactions. This process generates energy that is used to pump hydrogen ions and create ATP. The video emphasizes its role in the flow of electrons and production of energy.

💡ATP

ATP, or adenosine triphosphate, is the main energy carrier in cells, produced during the light-dependent reactions of photosynthesis. The video explains that ATP, along with NADPH, provides the energy required for the Calvin cycle to synthesize glucose.

💡NADPH

NADPH is an energy-rich molecule generated during the light-dependent reactions and used in the Calvin cycle to help synthesize glucose. In the video, it is referred to as a carrier of hydrogen ions, similar to a taxi, helping to transfer these ions to where they are needed in the photosynthesis process.

💡Stomata

Stomata are small openings on the underside of plant leaves that allow for gas exchange. The video discusses how stomata take in carbon dioxide and release oxygen, playing a crucial role in the exchange of gases during photosynthesis.

Highlights

Photosynthesis is more complex than just sunlight, water, and carbon dioxide producing oxygen and glucose.

The Sun's energy travels as waves, with visible light being key to driving photosynthesis.

White light is a mixture of colors (ROYGBIV), proven by the dispersion of light through a prism.

Red light has a longer wavelength, while violet light has a shorter wavelength.

Objects appear colored due to the reflection and absorption of specific light wavelengths.

Green leaves reflect green light but absorb other colors to power photosynthesis.

Blue and red light are the most effective for photosynthesis, while green light has the least impact.

Photosynthesis converts solar energy into glucose using carbon dioxide and water, releasing oxygen as a byproduct.

Autotrophs, including plants, algae, phytoplankton, kelp, and cyanobacteria, perform photosynthesis.

Photosynthesis is an endergonic reaction, requiring energy input from sunlight.

Chloroplasts are the cell structures responsible for photosynthesis, with thylakoids hosting the light-dependent reactions.

The light-dependent reactions produce oxygen, ATP, and NADPH in the thylakoid membranes.

The Calvin cycle (light-independent reactions) occurs in the stroma and produces glucose.

Photosystem II absorbs sunlight, exciting electrons that drive an electron transport chain.

ATP synthase creates ATP during the light-dependent reactions by using a concentration gradient of hydrogen ions.

Transcripts

so today's videos on photosynthesis and

you know it might seem pretty

straightforward he shines from sunlight

you sprinkle some rainwater you add some

carbon dioxide from the atmosphere and

through photosynthesis plants will give

off oxygen and will create simple sugars

such as glucose but you know the actual

process is a lot more complex so let's

get started so the Sun gives off a

variety of types of energy and this

energy travels across space in the form

of a wave and the titles of the energy

you can see at the top of the picture

now we're going to focus our attention

on visible light because it's the

wavelength of visible light that drives

and powers photosynthesis well let's

focus on how light is absorbed and when

we do we're gonna see that the Sun gives

off visible light also called white

light white light is actually a mixture

of ROYGBIV and what this is are the

colors of the rainbow red orange yellow

green blue indigo violet all of these

colors are a mixture known as white

light well how do we know this because

when you shine light into a prism when

you shine white light into a prism a

rainbow comes out the other end just

like you can see in this animation white

light is entering from the left and

because of the curvature of the prism

ROYGBIV the colors of the rainbow are

coming out the other end

notice how the wavelengths are different

red has a longer wavelength the violet

has a more narrow and so this is how we

know that white light is made from a

mixture of these colors here is an

actual picture of white light entering a

prism and you can see on the left-hand

side a rainbow is coming out the back

end

you know moisture in the air can act

like a prism and create a rainbow

you ever notice after it rains you can

sometimes see a rainbow in the sky or in

this case near a waterfall because of

all the moisture in the sky the moisture

separates the light the sunlight into

the rainbow colors that you see

and so colors are either reflected or

absorbed when sunlight shines on an

object what we see is reflected light

the reason this leaf appears green is

because it's reflecting the green

wavelength of light when light shines on

these bananas the reason it appears

yellow is because the yellow wavelength

reflects while the other color colors

are absorbed when we shine light and

these balloons the blue wavelength

reflects into our eyes and the other

colors are absorbed when we look at

white objects like snow or this arctic

hare the reason objects appear white is

because white reflects all the colors

and all the light all the wavelengths of

light enter our eyes and our brain

interprets this as the color white well

the opposite will be black when light

shines on a black object

nothing reflects it always absorbed and

that's why this automobile pairs black

because there's no light reflecting into

our eyes so when we relate this to

photosynthesis plants have you know

mostly green leaves which means that

they're gonna reflect the green

wavelength but the other colors are

absorbing into the leaves and are going

to be powering photosynthesis in this

graph we can see for instance that this

graph shows the wavelengths of light

that most powerful synthesis notice how

there's a peak around 400 nanometers

well that's the wavelength of blue

there's another peak around 700

nanometers well that's a wavelength of

red so blue light and red light are most

stimulating for plants in the process of

photosynthesis ironically the color

green around 550 nanometers the color

green that we most associate with plants

actually has the least amount of impact

in their ability to do photosynthesis

that's because most green light is

reflecting very little green light is

actually absorbing into the leaf

so when we look at a general definition

of photosynthesis you know it's the

process that converts solar energy into

glucose and this formula here outlines

photosynthesis and in the reactants we

have carbon dioxide and water and in the

presence of sunlight will produce sugars

such as glucose and oxygen well who who

performs photosynthesis well these are

the autotrophs now we typically think of

plants as doing photosynthesis but

they're not the only ones algae

phytoplankton the basis of ocean food

webs kelp kelp can grow into these

enormous underwater forests and even

some bacteria known as cyanobacteria are

photosynthetic so there's a lot more

autotrophs than just plants so

photosynthesis is also what we call an

endergonic chemical reaction and what

that means is that photosynthesis

requires the input of energy from the

picture I'm implying that sunlight

sunlight is the energy that is input to

power photosynthesis and when we talk

about the end result what's created well

oxygen which is a waste gas and simple

sugars like glucose but when we zoom out

into the leaf we find some peculiar

pores on their underside these pores

will open and close and they're called

stomata and it's how they exchange gases

it's how they take in carbon dioxide

from the atmosphere and when they

produce oxygen as a waste through these

stomata openings they give off the

oxygen created so it's through these

pores that they exchange gas with the

atmosphere

okay so now let's introduce the

structure in cells that allows them to

do photosynthesis and this is the

chloroplast what we're gonna do is we're

actually actually gonna divide

photosynthesis into two stages stage one

being the stage that depends upon

sunlight the light dependent reactions

and these take place in the thylakoid

membranes of a chloroplast you know I

want to actually look at a more

simplified diagram here and when we do

we can actually see the thylakoids

which kind of look like coins or

frisbees stacked on top of one another

well in the membrane of these thylakoids

is where the light dependent reactions

occur and if you ever come across the

term Granum that's a term that I mean

that that means a stack of thylakoids

okay so you see that flashing black box

I want to zoom into that area of the

chloroplast and when we do we're gonna

see that there are some things actually

embedded within the membrane of the

thylakoid i've labeled them ps1 and ps2

and these are the photosystems and we're

going to talk about them in more detail

but for now in the photosystems is where

we find chlorophyll and various protein

molecules that are responsible for

capturing and transferring energy during

the light dependent reactions and it's

during the light dependent reactions

where oxygen ATP and something called

NADPH is created we'll talk about these

molecules in more detail coming up very

shortly and then we'll show it will

shift into stage two the light

independent reactions and this happens

that occurs in the stroma the

fluid-filled interior of the chloroplast

just outside of the thylakoid and it's

in stage two the light independent

reactions where glucose is actually

created so let's talk about these two

stages for the rest of this video

so now let's get into some of the

details of the light dependent reactions

and what we're gonna do is we're gonna

break this down into a few steps so step

number one chlorophyll in photosystem

number two will absorb sunlight now even

though it's called for photosystem

number two it's actually the first and

the chain of events they were named

photosystem 1 and photosystem two by

order in which they were discovered not

the order in which they perform their

function so you kind of have to get over

that backwards name right there so in my

animation sunshine sunlight is striking

the chlorophyll molecules in photosystem

number two and this causes their

electrons to become excited and what

happens is the electrons actually flow

into the thylakoid membrane and so as

these electrons from chlorophyll in

photosystem number to flow through the

thylakoid membrane this makes the

membrane negatively charged and as the

electrons are flowing through there's

also proteins embedded within the

thylakoid membrane that are eating their

travel I just didn't show them in my

animation but this starts what we call

an electron transport chain it's a chain

of events setting forth by these set in

motion by these electrons so when we

move on into the second step I've added

some hydrogen ions into the stroma

because there's dissolved molecules and

ions in the stroma

and these hydrogen's are going to play

an important role and so what happens is

as the electrons move through the

thylakoid membrane they actually will

operate any power and turn on these

protein pumps that will pull the

hydrogen's into the thylakoids

and as more and more and more hydrogen's

accumulate this is gonna make a really

large concentration of hydrogen's which

we'll see why that's important in a

little bit I also want to mention that

water molecules are broken so here's a

water molecule and with the help of

enzymes the hydrogen's are broken off

and the electron from the hydrogen went

into photosystem number two here we go

again enzymes will break off the hydro

and notice how the electrons were pulled

into photosystem number two you know

photosystem number two has been losing

electrons and so it's waters the

hydrogen of water it's their electrons

that will replenish photosystem number

two so it doesn't run out of electrons

and so this process can keep going this

is why you have to constantly water a

plant also oxygen this is where the

oxygen comes from see that Oh for oxygen

it will bond with another Oh from

another water that was broken to make Oh

to the oxygen that we breathe used to be

attached to water which I think is kind

of interesting so as we move on into the

next step again sunlight is striking

photosystem number two and it's

electrons are moving through the

thylakoid membrane but you know sunlight

is also striking photosystem number one

and photosystem number one is filled

with chlorophyll and it has electrons

that also become excited and move

through the thylakoid membrane so what

we really have is kind of a longer

electron transport chain so now that we

have our full electron transport chain

let's move on to the next step and in

the next step a molecule called NADPH

will be created so in the stroma and adp

and a hydrogen are drawn together and

the electrons of the electron transport

chain help these to bond together to

make a really important molecule called

NADPH NADPH can be kind of be kind of be

viewed as a carrier of hydrogen like a

taxi whose job it is to carry hydrogen

from one place to another we'll come

back to it in a little bit but it's

really important that NADPH was just

created so at this stage the hydrogen is

really beginning to accumulate inside

the thylakoid from the breaking of water

from the electron transport chain

pulling in hydrogen's from the outside

so by now there's a really large

concentration of hydrogens inside the

thylakoid so when we come to our next

step

because there's such a large amount of

them the hydrogens are going to start to

diffuse through that the enzyme labeled

ATP synthase and so what hydrogen does

from a high to low concentration it will

diffuse through ATP synthase and will

help to bond a molecule of adp adenosine

diphosphate with another phosphate and

when that happens they bind to make a

molecule of ATP and so this ATP along

with the NADPH are really the most

important things that are created during

the light dependent reactions we're

gonna see what's so important about them

in just a little bit and so to summarize

the light dependent reactions oxygen

NADPH and ATP have been created

you know sunlight was taken and water

was taken in and oxygen was released as

a waste and in the light dependent

reactions NADPH and ATP have been

created I do want to note at this stage

no glucose has been created so let's

move on to the light independent

reactions ok so the light independent

reactions you know this is also known as

the Calvin cycle named after the

scientist who helped to identify these

steps and so we're gonna start breaking

it down first of all there's a five

carbon molecule by the name of rubp

ribulose biphosphate now it has more

than just five carbons you can see 12

hydrogens 11 oxygens and two phosphorus

'iz but for simplicity I've only drawn

the five carbons of rubp

and what happens is rubp bonds with a

molecule of carbon dioxide and when they

bond they make a very short-lived six

carbon molecule the five carbons from

rubp plus the one from carbon dioxide

make this very short-lived six carbon

molecule so the reason the six carbon

molecule is short-lived

is we finally get to see the importance

of ATP and

DPH which were created during the

light-dependent cycle the six carbon

molecule is gonna be broken down by the

energy contained within ATP and nadph in

enzymes will help to break down ATP and

nadph to release their energy and when

the energy is released that six carbon

molecule is broken down into two

molecules called phosphoglycerate each

pga or phosphoglycerate is three carbons

in size and by the way the nad p and the

adp that are left over will be reused

and recycled in the next light dependent

reaction and so this happens multiple

times here's another short-lived six

carbon molecule broken down by NADPH and

ATP to make two more molecules of

phosphoglycerate and it was another six

carbon molecule broken down by another

NADPH and another ATP to make two more

molecules of the phosphoglycerates

so what happens now with these

phosphoglycerates well some of those

three carbon phosphoglycerates are gonna

bond with one another and with the help

of enzymes they're gonna bond to make

simple sugars such as glucose and that's

the whole point of photosynthesis is to

make glucose now not all the

phosphoglycerates do this some of the

phosphoglycerates are going to help to

keep the cycle going and so what happens

is they're gonna be broken down they're

gonna be broken down with the help of

ATP to keep the cycle going and when ATP

breaks some of these other

phosphoglycerates down they're broken

down and then enzymes help to build that

same 5 carbon molecule we saw earlier

ribulose biphosphate and now we're

repeating the calvin cycle the light

independent reactions the process simply

restarts because carbon dioxide will

bond with this five carbon rubp when

they bond they make that short-lived six

carbon

like he'll that we mentioned earlier and

the process repeats itself

so to summarize the light independent

reactions carbon dioxide ATP and nadph

are going to create glucose so when

carbon dioxide is added to the ATP and

nadph from the light dependent reactions

with the help of enzymes you have simple

sugars such as glucose created okay so

if you're in my biology class we'll talk

about this essay question in class

and there you have it as we wind down

this video

you know pause it try to answer these

questions and you know put your comments

in the box below I hope you found this

video helpful thanks for watching