Photosynthesis (in detail)
Summary
TLDRThe 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
- đ Photosynthesis is a complex process that converts sunlight into glucose and oxygen, utilizing carbon dioxide and water.
- đ Sunlight, also called white light, consists of a spectrum of colors (ROYGBIV), and these different wavelengths play a key role in photosynthesis.
- đ Plants appear green because they reflect green light while absorbing other colors, particularly red and blue wavelengths, which are most effective for photosynthesis.
- đ Photosynthesis involves two main stages: light-dependent reactions (occur in the thylakoid membranes) and light-independent reactions (occur in the stroma of chloroplasts).
- đ During the light-dependent reactions, sunlight excites electrons in chlorophyll, which initiates the electron transport chain and produces ATP and NADPH.
- đ§ Water molecules are split during the light-dependent reactions, providing replacement electrons for chlorophyll and releasing oxygen as a byproduct.
- đ The Calvin cycle (light-independent reactions) utilizes ATP, NADPH, and carbon dioxide to produce simple sugars like glucose.
- đ 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).
- đ Some of the produced molecules (PGA) help create glucose, while others regenerate RuBP, allowing the Calvin cycle to continue.
- đ± 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
đ 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.
đ 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.
đ 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 stomataâtiny 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.
đż 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.
âïž 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.
đ± 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.
đ 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.
Mindmap
Keywords
đĄPhotosynthesis
đĄChlorophyll
đĄThylakoid
đĄLight-dependent reactions
đĄCalvin cycle
đĄAutotrophs
đĄElectron transport chain
đĄATP
đĄNADPH
đĄStomata
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
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