Hey everyone! Dr. D. here and in this
video we're actually covering chapter 8,
Photosynthesis! Let's go ahead
and get started. So, you may know that
photosynthesis happens in plants and
other green organisms, but what is it?
Okay, photosynthesis is a process that
converts solar energy- that's the sun's
energy- into chemical energy. Usually
sugars, so you're taking sunlight
energy and through a series of
conversions (remember you can convert
energy from one form to another), you're
forming chemical energy in the form of
sugars right? And directly or indirectly,
photosynthesis nourishes almost the
entire living world. What does that mean?
The calories you are getting in your
diet originated in by
photosynthesis is what that means. So,
even if you're a strict meat-eater and
you eat only beef let's say, you
just love having chicken and beef and
I don't know pork and whatnot. What did
those animals eat? You know they ate
usually photosynthesizers for
nourishment so you could trace your
calories back to a photosynthesizer.
What that means is if plants were to go
away, so would our source of nourishment,
our source of calories, and so we would
also perish. So, they're very
important and because they can make
their own calories, they're called
autotrophs so autotrophs can sustain
themselves without eating anything so a
plant doesn't need to eat
another organism to stay alive. It uses
the sun's energy, converts that type of
energy to chemical energy, those
calories- those sugars, and those fats
right? Okay autotrophs are producers of
the biosphere they can take CO2 out of
the air and convert it. They can
take the CO2 in the air to make sugars out of
it which is really cool so that's
another way that these these
photosynthesizers help us they take CO2
out of the air and they actually convert
the CO2 to sugar which is super helpful
to us. And of course you know plants also
produce oxygen. so that's also super
important to us. There are three reasons
why photosynthesizers are required for
our life here on earth and by 'our', I mean
heterotrophs'. Heterotrophs are creatures
like you and me that cannot sustain
themselves. We require those autotrophs
for sustenance. We are the consumers of
the biosphere, right? We
need those photosynthesizers for oxygen,
for sugars, and fats that they produce. For
removing CO2! You know this harmful
greenhouse gas, from our environment as
well, so let me put it this way without
plants and without other
photosynthesizers on this planet, humans
could not live on this planet and if
humans ever decided to go to another
planet, we couldn't do so without
bringing along a friend! And that friend
being a photosynthesizer friend. And many
of them that's why plants are very, very
well suited for the planet Earth they
can produce their own carbon dioxide
they can produce their own oxygen they
can, in fact, can I'll get to
this, but you could stick a plant in a
jar and close that jar off at the plant
could live inside the jar whereas a
human if you put a human in a jar and
close that jar off the human would soon
breathe all the CO2 and pass away, right?
 I'm sorry, I mean breathe all the oxygen
converting it to CO2 and then pass away
from that. So, I'll explain why that is in
in a minute. You understand why a plant
could live in a jar but an animal or a
human couldn't live in a jar?
Let's explain this, oh by the way
let me just show you the types of
photosynthetic organisms there are,
photosynthesizers there are you know if
it's green it's it's most likely a photo
synthesizer but not all
photosynthesizers are green. Let me
show you what I'm talking about plants
are obviously green you know their
leaves anywhere that you see green
leaves and things that's because of
chlorophyll a photosynthetic pigment
that allows photosynthesis to happen and
that pigments in the leaves right the
structures of the mesophyll, which I'll
explain in a minute. The algae! Algae, as
well as photosynthetic protists. So,
all three of these are eukaryotes plants,
algae, protists. And, protists can be
single-cell creatures like euglena
which are photosynthetic right so you
can even have little single-cell
creatures also cyanobacteria which
is a type of bacteria, that's a huge
portion or proportion of the
photosynthesizers on the planet but
here's an example of a purple sulfur
bacteria is an example of a non green
photo synthesizer. Okay, so most most of
the time when you're talking about
photosynthesis you're talking about
green creatures, whether it be eukaryotes
like these on the left or prokaryotes
like these on the right, but you don't
necessarily have to be green as long as
you're doing the process of
photosynthesis. So let me explain real
quick- in a plant where these
photosynthesizing cells are leaves right
the leaves of the plant are usually
green right the leaves of a plant are
usually green and that's because the
green color is from this molecule
chlorophyll. Okay, the green color is from
chlorophyll it's a pigment it's a
pigment molecule and chlorophyll is
responsible for utilizing that sunlight
energy trapping that sunlight energy and
using it to power photosynthesis or at
least
light reactions of photosynthesis, which
we're gonna talk about soon. And where
are the chlorophyll molecules? They're
inside certain cells that have
chloroplasts. The cells that have
chloroplasts, these cells are found in
the mesophyll of the leaf.
What's the mesophyll of the leaves? Let
me show you. If we're talking about a
leaf on a plant on a tree then if you
cut open go do a cross-section of that
leaf you'll see this is the upper dermis
of the of the leaf this is the lower
dermis then you've got little holes
where gas exchange happens on the bottom
side of the leaf. You got little pores
called stomata this is where CO2 net
flows into the leaf and O2 net flows out this is why they say plants breathe
in CO2 and breathe out O2 and pretend
we can use that O2 to breathe. But
where are the chloroplasts? Look the
cells that are in the middle, the
cells of the what are called mesophyll
of the leaf. Those cells contain the
chloroplasts and there's 30 to 40 chloroplasts typically in
each of those mesophyll cells so look.
This would be a cell in the
mesophyll right here. It would have 30 or 40 chloroplasts inside.
And it's those chloroplasts which I-
remember those organelles membrane bound
organelles that's where the chlorophyll
pigment molecule lives. Okay, so we're
gonna talk about that. And this is what
the chloroplast looks like remember each
mesophyll cell has about 30 or 40 of
these inside these organelles called
chloroplasts. The chloroplast have an
outer membrane, an inner membrane, but
then inside of that, it's got these
stacks of membrane- you see this? It looks
like a little stack. I affectionately call these
'pancakes stacks'
you know that's obviously not what
they're technically called but I call
them pancake stacks because it makes it
clear that this is what I'm talking
about.
Each stack of these pancake looking
things- each stack- is called a granum.
Granum, here's the word here granum. The
plural for Grana.
Each pancake in the stack, you
see how the stack has a bunch of
pancakes? Each pancake in the stack is
called a thylakoid. So again,
the whole stack is called a granum,
multiple stacks is called a grana, and
each pancake in the stack is called a
thylakoid. You see? The fluid
outside of the pancake stacks? This fluid right outside the pancake
stacks, that fluid's called the stroma. 
And, do you see the fluid inside of the
pancake stacks?That's called the
thylakoid space. So again, here's a
chloroplast. You have the outer membrane and you have the inner membrane
underneath it. And then you have these
stacks of membrane called Granum.
each pancake in the stack each component
of the stack is called thylakoid the
fluid outside the stacks is called the
stroma the fluid inside of the stacks is
called the thylakoid space okay so
that's the architecture of the
chloroplast and remember each miso fill
cell contains 30 or 40 you can see those
dirty or 40 chloroplasts here and those
Muzo fill cells are in the middle of the
leaf okay in the middle of the leaf and
that's why the leaf is green you know
why because the chlorophyll molecule is
inside the chloroplast now you might be
wondering where is the chlorophyll
exactly inside of the chloroplast so
here's the coroplast okay
you see how they drew the pancakes tax
the Granum green they did that for a
reason the chlorophyll molecule the
chlorophyll molecule the pigment that
makes the leaves green that pigment is
found in the pancake stack membrane so
what is that called that's called the
thylakoid membrane the membrane of the
pancake stacks that membrane is called
the thylakoid membrane and that makes
sense right this is this membrane right
here on the pancake stacks that's called
the thylakoid membrane you should know
that and that's where the chlorophyll
molecules are that's why the leaf is
green because those core FL molecules
are agreed okay now what is the equation
for photosynthesis let's use this
equation let's use this equation for
photosynthesis first of all take a look
at this equation take a second to look
at this equation what did what what do
you see does this equation look familiar
in any way I'll give you a second to
check it out if you've if you said it
looks like cellular respiration but
backwards then you'd be exactly right
cellular respiration would be oxygen 6
oxygen and a glucose molecule which gets
converted to water six water six co2 and
energy in the form of ATP right well
notice how photosynthesis is the
converse reaction converse means
opposite reaction right in this case
you're taking not ATP energy you're
taking sunlight solar energy you're
taking six co2 you're taking six water
and you're producing glucose
and six oxygens so it is the converse
reaction to cellular respiration so
cellular respiration the arrow is going
this way and the energy you're making is
ATP photosynthesis the arrows going the
opposite way and the energy you're
making is or the energy you're using I
should say in this case with photos that
this is the energy you're using a solar
energy that's the only difference
between the two net equations okay so do
you remember earlier when I said that
plants can live inside of a jar but
humans cannot live inside of a jar right
so if you put a human inside of a jar
and close the jar that wouldn't be a
good plan right because the human would
soon do what this the human remember the
humans have cellular respiration and
that means the arrows going toward the
left so humans would consume oxygen and
then and sugars to make co2 right and
water as products and at some point
you're gonna consume all of the oxygen
inside of that jar right and you're
gonna convert it to co2 or at least
you're gonna use it to convert the
glucose into co2 right so that's the
problem with you know being in the jar
you're using up all the oxygen you're
gonna run out of oxygen and you're gonna
pass out in the jar all right so why
don't plants pass out in the jar right
so look what plants can do they can do
photosynthesis which is an arrow this
way which means they take co2 and water
to produce sugar and oxygen now you
might ask okay that's great they're
producing oxygen but what about using up
co2 at some point they're gonna use up
all their co2 right no you know why
because plants have a trick up their
sleeve plants not only do they have
chloroplasts which do what
you see coroplast s-- do this reaction
where they take co2 and water to make
sugar and oxygen guess what
plants also have mitochondria like you
and me you know how we have mitochondria
which allows us to take oxygen and
glucose to make co2 and water plants
also have mitochondria so plants have
mitochondria which produces what
mitochondria produces co2 and they also
have chloroplasts which produce Oh too
so imagine if you could do if you had
chloroplasts and you could do this
reaction making sugar and oxygen but you
also had mitochondria which could do the
opposite and use that sugar and use that
oxygen to make more water at co2 do you
see if you have an organelle that does
this reaction and you have another
organelle which uses those products to
do the converse reaction well then you'd
never run out of anything to breathe
right you've never run out of co2
because you can make more co2 you you'd
never run out of o2 because you could
make more o2 the reason a plant doesn't
suffocate in a jars because it has both
organelles it has the chloroplasts and
it has the mitochondria so it can use
the waste products of one as the
reactants of the other process and so
it's like this infinite loop where you
never run out of your own you know a
resources humans on the other hand
because we don't have chloroplasts we're
gonna convert all that oxygen and we're
gonna produce co2 I should say you use
up all the oxygen produce a bunch of co2
and so once we've used up that oxygen
we're gonna pass out right
so that is why there's this fundamental
difference and that is why if humans
ever have to go to live on another
planet like Mars we're gonna need to
break plants with us because we're going
to need a source of oxygen we don't we
don't have a source of oxygen on this
planet or any
their planet without without something
that produces oxygen like one of these
autotrophs
what are these creatures
photosynthesizers that has chloroplasts
so that's pretty cool to talk about so
let me take a quick break you're gonna
go and get a fresh coffee now be right
back and I'll tell you about this super
interesting super important process that
makes life possible on this planet of
Earth photosynthesis what I get back
break time hey everyone welcome back
let's get started so I was just telling
you that photosynthesis is the process
of converting solar energy light energy
oops sorry
light energy using light energy to
convert co2 and water into sugar glucose
and oxygen okay so during this process
the co2 is going to become reduced
okay the co2 is going to become reduced
and the water is going to become
oxidized okay
so how does that work what it remember
what reduced means gaining of electrons
co2 is gonna gain electrons not only
electrons but protons as well it's gonna
get H's right do you guys remember do
you remember the the equation for sugars
because what are we trying to do we're
trying to take co2 out of the air right
that's what the plant breathes in when
the plant breathes in it breathes it
mostly co2 okay and co2 is in the air as
a gas and what are we trying to do with
it do you remember we're trying to make
sugar out of co2 that's the main thing
we're trying to accomplish in
photosynthesis
we are trying to make sugar out of co2
but co2 is a gas and look at look at
what co2 is made out of it's made out of
a C and two O's right
what's sugar made out of do you guys
remember the chemical formula for sugars
remember sugars have c h n o the
elements see carbon h hydrogen and o
oxygen and do you remember the ratio of
C's H's a nose do you guys remember that
there's one carbon for every two
hydrogen's for every one oxygen so it's
a ch2o ratio right do you remember for
example glucose what's glucose c6h12o6
you have C's H's Atos and a one to two
to one ratio of C's HS and O's so look
if we want to take sees and knows and
make glucose out of it we have to give
it what it already has the seas and the
O's what do we have to give it HS we
have to give it H is so it becomes C h o
c6 h-12 o-6 which is glucose where did
the HS come from where did the ages come
from magic no that's where water comes
in look we need water as a reactant
reactant means starting material
remember that we need water because it's
the it's the source of our H is of our
electrons right and again please
remember when I say electrons HS are
more than just electrons aren't they H's
are an electron and a proton but we call
them a source of electrons because
that's the main thing we care about but
don't forget it's not just an H it's an
H and a and a proton so anyway you're
taking water
you're taking the H's from the water and
you're handing the H's to the carbon
dioxide to make sugar to make sugar okay
and what's left over once you've taken
all the H's from water what's left over
oxygen this is why the plant net
breathes in carbon dioxide because it's
gonna reduce the carbon dioxide to sugar
and it net breathes out oxygen because
that's what's left over of the water
once you've oxidized the water once
you've removed its electrons it does
remove those H's and handed those H's to
the carbon dioxide to make sugar so
again just to review carbon dioxide gets
reduced to glucose because you're giving
it electron so remember gain of
electrons means reduced water is a
source of up those electrons so water is
losing those electrons water is becoming
oxidized to oxygen okay
so just remember that so it summarized
here look carbon dioxide is becoming
reduced to glucose see the difference
between co2 and glucoses it's gained a
bunch of HS right it's gained a bunch of
electrons it's become glucose c6h12o6
and meanwhile water water has become
oxidized to oxygen that's where the HS
came from so think about this you're
taking the H's from the water you're
giving them to the co2 the co2 becomes
sugar and the water is left out as
oxygen that's now broken down into
oxygen and that process required energy
to happen you can't just make sugar for
free that energy is solar energy that
energy is from the Sun okay and that's
where the chlorophyll molecules come in
chlorophyll is the molecule that's going
to capture that sun energy solar energy
to make this process go so there are
actually two stages I want to show you
this this figure here because there are
two
stages two main parts to photosynthesis
the part on the left in this figure and
the part on the right in this figure
okay
there's two parts the first part to
photosynthesis is called the light
reactions and that requires light that's
why it's called the light reactions then
you're ready for part two the second
part of photosynthesis which is called
the calvin cycle this is the part that
actually makes the sugar okay so the
light reactions are the first part they
involved light and those chlorophyll
molecules and the second part is called
calvin cycle that's where you actually
make your sugar your ch2o multiples
right which is shook alright let me
explain just a bird's eye view a big
overview of house of how photosynthesis
works okay let me show you how this
process works look at the left here the
light reactions what are you doing and
again I just want to give you a big
overview and we'll get into details
later don't don't get confused don't say
oh well how exactly does that work I'm
not focusing on how exactly this works
right now I just want to show you the
overview so in your mind you can see the
big picture okay ready for a big picture
okay look the light reactions require
light light is hitting thee what is this
this pancake stacks you remember so this
must be the chloroplast you see this
whole thing I'm highlighting right now
this is the chloroplast which is the
photosynthetic organism fuel cells
remember there are 30 or 40 of these
each Meisel feel cell you got a
chloroplast inside of the chloroplast
remember you have these stacks of
membrane I call a pancake stats those
are called Granum so this is the Granum
and do you remember the membrane of the
Granum is called the thylakoid membrane
well the thylakoid membrane is where the
chlorophyll molecules are and the
chlorophyll molecules respond to light
light hits the chlorophyll molecules in
the thylakoid membrane and that's what
actually captures the energy from the
sunlight to make the light reactions go
and what do you do with that energy
here's what you're gonna do ready you
take water water is a reactant you take
water okay you're using the sunlight
energy to oxidize the water do you
remember what that means remove the H's
from water remove the electrons from
water what happens if you remove the H's
from water what's leftover
if I remove the H's from water what's
leftover oxygen you see and so the
product is oxygen do you see why oxygen
is a product of photosynthesis now
because the first thing you're gonna do
is take sunlight energy to remove the
H's from water and all that's left over
are OHS which is oxygen two of the OHS
find each other and leave as OH - that
leaves as gas oxygen gas for us to enjoy
for us to breathe right so where did the
H go where did the H go that it just
flowed off no the H is handed to an
electron carrier called
an a D P Plus this is the oxidized form
of the carrier this is an electron
carrier it does what its name suggests
it carries electrons so here's what
you're doing you're using sunlight
energy to remove the H's from water
you're handing those H's to what you're
giving those H's to and ADP plus and
that becomes what is nadp+ what happens
once you give it those electrons and a
proton it becomes NADPH and you don't
need to know this but you hand two
electrons and one proton to an ADP plus
so that it becomes NADPH okay so NADPH
is the reduced form of the electron
carrier right so now look you can think
of it this way the H is the h's and the
electrons you could call them the H's
the electrons on NADPH are the electrons
that were on the water so the water is
the primary electron donor here the
water is where the electrons are coming
from sunlight energy allows you to
remove those electrons hand them to the
electron carrier the electron carrier
becomes reduced to an ad pH now you have
NADPH
you now have the H's from the water on
NADPH and the oxygens from water are
floating off as waste gas now here's a
thing that happens as well look because
of this process of the light reactions
in the Granum you're also taking ADP and
inorganic phosphate and you're making
ATP so you're making some ATP as well
now again I'm not going to tell you
right now exactly how this ATP is made
but for now just know that during the
light reactions not only are you
oxidizing water to oxygen and handing
its electrons to the electron carrier
nadp+ to form NADPH you're also forming
some ATP which is nice and that ATP is
formed by a process known as photo
phosphorylation okay so now let's
summarize real quick let's summarize the
light reactions of photosynthesis you
take light you use the light energy to
oxidize water and the waste product is
called oxygen the electrons are handed
to the electron carrier nadp+ which is
then reduced to NADPH and as a nice
little side bonus you've formed some ATP
as well through a process known as photo
phosphorylation great so the products of
of the light reactions are
ATP and nadph and the waste product is
oxygen the reactants were water and
sunlight okay those are them that's the
main concept I should say to the light
reactions of photosynthesis which happen
basically in the Granum of the
chloroplast okay so now you're ready
have you made sugar yet we haven't made
any sugar yet that's why we're gonna do
the Calvin cycle
so the Calvin cycle is where you
actually make your sugar and how do you
make sugar do you remember I set this
earlier to make sugar you need C's h's
and oh right that's the recipe for sugar
you need C's HSN O's to make sugar and
not only do you need C's HS and O's you
need a one to two to one ratio of CHS
and O's a 1 to 2 to 1 ratio of CHS and
O's so where do we get our season our
O's see we take co2 that's our source of
C's and O's for sugar and plants take
that co2 from the air and this is why
plants are so neat
they reduce the co2 in the air because
just like we breathe in oxygen and
breathe out co2 as a waste product
plants breathe in more co2 and breathe
in more oxygen ok so they're they're
taking they're like little carbon
dioxide sponges right there taking the
co2 out of the air with their stomata
remember they're little breathing pores
underneath their leaves they take the
co2 out of the air now is that a sugar
co2 is that of sugar no you need to give
it a cheese right do we have some HS
anywhere that we could give to the co2
to make sugar where do we have H's oh do
you remember this look what did we make
during the light reactions n/a d pH
there's there's a bunch of H's right
there right electrons and protons right
HS right where did those HS come for
they came from water originally you see
that the H is from water were given to
nadp+ to make NADPH now we have these
ages so guess what the Calvin cycle is
all about guess what the Calvin cycle is
all about in this cycle you're going to
take co2 you're going to give it a
choose from NADPH you're gonna give it
the H's when when NADPH reduces co2 that
co2 becomes seize HSN Oh sugar you see
that co2 is reduced to sugar because
NADPH reduces co2 to sugar and do you
think it's free to do that do you think
energetically energetically that can
happen for free no the answer is no you
can't just make sugar for free it's not
negative Delta G reaction so guess what
that's why you need the ATP that you
made during the light reactions the ATP
that you made during the light reactions
you're going to use ATP power to reduce
the co2 to sugar you to give these a
choose from NADPH to co2 to make sugar
does that make sense because it's not a
free thing to make sugar okay and once
once NADPH has reduced co2 to sugar and
empty PHS reconverted back to the
oxidized form of the carrier and ADP
plus and you can keep this going on
right you can keep photosynthesis going
on so that's how you made sugars you see
in step one you use sunlight energy to
oxidize water to take its H's away give
those H's two nadp+ to make NADPH and
some ATP and step two co2 was reduced to
sugar because those ages from NADPH were
given to co2 to reduce co2 to sugar and
that was with the help of the energy
from ATP so that's the big big overview
of how photosynthesis works it's
actually a really really neat process
right so if you think about it this is
the process that's responsible for a
while
on earth and the process that we need if
we are to live on any other planet we'd
need to take plants with us you know so
it's really neat to understand how
photosynthesis works and again
photosynthesis is based on sunlight
right without energy without without
solar energy without light energy I
should say photosynthesis would be
impossible without light okay and light
is a series of wavelengths okay light is
a form of electromagnetic energy also
called electromagnetic radiation but
it's a certain range of wavelengths of
electromagnetic radiation those
wavelengths are called visible light
okay so here's a here's a range of
electromagnetic radiation all the way
from very small wavelengths you know
because this radiation travels in
wavelengths right it travels in waveform
waveform and you can have tiny little
waves that means that the peaks and the
valleys are tiny in the wave or you
could have really big waves where the
waves are meters big right so the
tiniest the tiniest wavelength electro
magnetic radiation as the gamma rays
right ten to the minus five nanometers
nanometer is ten to the minus nine
meters right so this is ten to the minus
five nanometers which is super tiny
right and we're talking about in the
Pico metre or femtometer range these are
tiny tiny tiny wavelengths so you know
the wavelengths are these are for gamma
rays and then ten to the minus three
nanometers would be x-rays and one
nanometer would be UV rays but these are
types of energy that we can't see you
know you can't see x-rays or gamma rays
or UV ray
you can't see that even though that kind
of radiation exists what we can see is
this range right here this range we are
our human eyeballs can only see in this
little range right here and this range
of electromagnetic radiation is called
visible light it spans from 380
nanometers which is purple light through
450 and 500 nanometers which is blue
light through 550 which is green light
600 is yellow light 650 which is about
orange light 700 nanometers and 750
nanometers which is red light so from
purple or violet all the way to red
that's the spectrum that our eyeballs
can see and this is the range of my
radiation that our eyeballs pick up with
our rods and cones and pick up and sense
as different colors of light okay this
is what our eyeballs can see if the
wavelength is bigger than that like
infrared microwave or radio wave our
eyeballs can't see it if the wavelengths
shorter than that like UV x-ray or gamma
rays our eyeballs can't see it okay so
the shortest wavelength of light that we
can see is around 380 nanometers this is
violet light and what you need to know
is shorter wavelength light is higher
energy longer wavelength light like red
light is lower energy okay and plants
plants look green okay I'm gonna explain
why that is in a second why are plants
green well because plants absorb light
besides green okay if something is great
it's because it's absorbing the light
colors except for green okay so over do
you remember plants have these pigment
molecules in them mainly mainly
chlorophyll there's chlorophyll a
there's chlorophyll B we're going to
talk about those in a second but the
chlorophyll molecules live in
the thylakoid membrane remember the
membrane of the pancake stacks in the
Granum that's where the chlorophyll
molecules exist all right and why why is
the core fill why is it green and why is
the chloroplasts green well because of
this look sunlight comes down and the
visible light hits visible light hits
the thylakoid membrane right the
membrane of the pancake stacks and
here's what you need to understand
chlorophyll molecules absorb the rainbow
of light of visible light wavelengths
but it doesn't absorb green what does
that mean Green gets green passes right
through which is called transmitted
light green passes right through and
green gets reflected away okay so do you
remember this wavelength 550 525 550 the
chloroplast does not absorb does not
block absorb means block right or use
you know utilize the the chlorophyll
does not use the green light the green
light goes right through that's
transmitted and the green light is
reflected so if you see my shirt as blue
my shirt is blue because the sunlight
from outside which is white light white
light is your eyeball seeing all the
colors of light at once that white light
hits my shirt my shirt absorbs all the
different colors of light all the
wavelengths except for blue light which
is remember around 450 nanometers and
then that blue light reflects off my
shirt and goes to the camera for your
eyeballs to see okay and this is what
that molecule looks like chlorophyll
chlorophyll looks like this it's an
organic molecule with a cofactor
magnesium is a cofactor all right and
you don't need to know this exact
structure but I
put that here to show you that this is
what the molecule looks like chlorophyll
a has a methyl group right here where as
chlorophyll B has a carbonyl group a
ketone carbon yogurt right here okay so
that's the only difference between
chlorophyll a and chlorophyll B and that
each one absorbs a slightly different
wavelength of light but it's that's not
a big deal but they say that chlorophyll
a is the main photosynthetic pigment
okay but these are the molecules that
make plants green okay so the reason
chlorophyll molecules are important is
because coral molecules get excited when
photons of light hit them especially
those photons of light that aren't green
you know the the different colors
besides green but they get absorbed by
the korra film molecule and what happens
when light strikes the chlorophyll
molecule is that the electrons inside of
the chlorophyll molecule the electron
goes to a higher energy state so the
electrons
you know how the electrons exists in
various orbitals well those electrons
move further away from the atomic
nucleus those electrons go to a higher
energy state and this is a type of
potential energy this is the type of
potential energy the sunlight moves the
electron to a higher energy state now
the electron wants to go back down to
its ground state and guess what when the
electron does go back down spontaneously
go back down to its ground state this
chlorophyll molecule actually releases
that trapped energy so you could think
of it as like a capacitor photon of
light hits the chlorophyll molecule its
electrons get boosted to a higher energy
state called the excited state when the
electrons then collapse back down to the
ground state spontaneously the
chlorophyll can then release that
trapped energy from the Sun so it's
almost like the Sun charges these
molecules up
those molecules go back down to
uncharged when they do they release
their own energy you know that they
transmit that energy on right so that's
kind of how the chlorophyll molecule
works so I'm going to take another quick
little break and when I come back and
explain exactly how this molecule
functions in the light reactions of
photosynthesis and and where is this
chlorophyll molecule where where does it
exist you know and it has everything to
do with these photo systems which I'll
explain when we return all right break
time welcome back so I was about to tell
you about the photo systems and how they
participate in photosynthesis but before
I do because first of all the photo
systems look like this and they're
involved in photosynthesis but let me
let me let me show you an overview real
quick before I before I tell you what a
photosystem is let me show you this
image here this is basically do you guys
remember the first part of
photosynthesis was called the light
reactions okay this is a summary of the
light reactions of photosynthesis this
right here so look what we have here
first of all you might see a membrane
see this membrane here see this membrane
here this membrane is curved like this
for a reason this membrane is the
thylakoid membrane remember it's the
curved Pancake membrane it's the
membrane of the of an individual pancake
in the grana pancake stacks right so
you've got the thylakoid membrane inside
of the chloroplast right and in this
membrane remember I said the chlorophyll
molecules exist in this vent
brain you see these little tiny green
dots these little tiny green dots are
the chlorophyll molecules right so the
green dots are in this structure this is
called photosystem ii see that's where
the green dots are that's where the
chlorophyll is and it's in this other
structure called photosystem one as well
so you've got photosystem two with
chlorophyll molecules
you've got photosystem one with
chlorophyll molecules so I'm gonna
explain to you in just a moment what
photosystems do how photosystems
work okay so but just know that you've
got photosystem two in the thylakoid
membrane and it responds to light it
then passes off electrons to look at
this thing it's got PQ plastoquinone
it's got cytochrome complex on PC you
know what this is right here these three
things P Q cytochrome complex on PC
these blue ones these this is a electron
transport chain this right here is an
electron transport chain PQ cytochrome
conflicts in PC is an electron transport
chain do you know what they what an
electron transport chain does just like
we learned in cellular respiration when
electrons cross an electron transport
chain like this you see where the
electrons are coming from photosystem 2
the electrons are going to photosystem 1
when electrons cross an electron
transport chain much like this right
here protons protons are pumped protons
are pumped into the thylakoid space why
because the electrons are moving through
the electron transport chain
spontaneously that provides the energy
that's the exergonic reaction that
drives the endergonic reaction here of
protons getting pumped actively into the
thala coit space the thylakoid spaces
the space or fluid inside of the pancake
stacks okay so now what would you have
here you would have a high concentration
of protons here in the Dalek oyd space
what do those protons want to do that's
right if you guess they want to diffuse
back to the stroma you would fluid
outside of the pancakes which has low
proton concentration or relative proton
concentration you'd be right but Ken
protons float through directly through
the membrane like this can protons go
out of the membrane directly no because
protons are charged right protons are
charged H+ is charged protons can't
cross the membrane directly so what did
the protons do they need a transporter a
carrier protein and that transporter you
guessed it this is the transporter
that's going to let those protons
chemiosmosis diffuse back out and that
that is called ATP synthase the top part
will spin the top part was been as the
protons force their way out and the
bottom part will produce ATP by joining
adp and pi inorganic phosphate together
to form ATP this is the ATP that's made
during the light reactions of
photosynthesis this is called photo
phosphorylation that's how you make ATP
during during this process of
photosynthesis and that ATP is going to
be used for a step to the Calvin cycle
okay that's great so again electrons so
the photosystem 2 responded to light
that's what allowed electrons to go
through the electron transport chain
that's what allowed protons to be pumped
actively into the dollar Koide space
those protons then diffused back out
into the stroma through Keamy osmosis a
exerting a proton motive force which
spun ATP synthase allowing ATP to form
that ATP is going to be used by the
Calvin cycle but where did those
electrons end up the electrons ended up
photosystem one and then the electrons
go to this protein called nadp+
reductase and the protons are given to
nadp+ the carrier to reduce it to NADPH
so the electrons make their way to NADPH
and those that NADPH moves off to the
Calvin cycle to donate those H's to make
sugars and where did these electrons
come from if we trace it all the way
back the electrons come from water it
looks like photosystem two steals the
electrons from water and those electrons
go on this journey to nadp+ to make
NADPH and those electrons end up on
NADPH and off to the calvin cycle and
once you've stolen those electrons or
those H's from the water all you're left
with from your water is oxygen so this
is an overview of what's called the
linear reaction or linear light light
system okay I should say linear electron
flow of of photosynthesis linear
electron flow why do they call it linear
electron flow the electrons start on
water the electrons then make their way
with the pep with the help of light the
electrons then make their way in a
linear fashion to nadp+ to make NADPH
and off you go to the Calvin cycle so
that's an overview of how the light
reactions work to photosynthesis but how
exactly are these photos systems working
you see this it looks kind of like an
apple this purple Apple
this one's called photosystem ii this
one's called photosystem one how in the
world are these photo systems working so
let's talk about that okay let's go back
to that remember the photo systems look
like these apples right this is a
photosystem this membrane is the thala
Koide membrane right the membrane of the
pancakes and this this this complex is
called
the photosystem it's a photosystem okay
and remember the green dots in the
photosystem the green dots are the kora
fill molecules and not only chlorophyll
but other pigment molecules as well we
haven't talked about them but you have
chlorophyll a you could have chlorophyll
B you could have xanthophyll or
carotenoids there are all different
kinds of pigment molecules what does a
pigment molecule mean again remember
it's a molecule that gets excited by
sunlight sunlight moves the electrons in
the pigment to a higher energy state
which is a type of potential energy when
Dozo when those electrons go back to
their ground state they release that
potential energy and that energy can be
bounced around that energy can be passed
off to other pigment molecules so let's
let's talk about it let's talk about how
that works
notice there are two parts to the
photosystem the purple part right with
the green dots that parts called the
light harvesting complex where the story
starts and then there's this blue part
in the middle the blue part in the
middle is called the reaction center
complex that's that's the second part of
the story so let's start with the first
part of the story because the
photosystem has two main parts the light
harvesting complex the purple and green
part and the reaction center complex the
blue part with the two green dots in the
middle so let's talk about this let's
let's start with the light harvesting
complex
k how does that work the light
harvesting complex this is a a protein
right here this is protein and inside of
the protein is these green dots which
are chlorophyll or different pigment
molecules okay you've got the pigment
molecules and sunlight traveling
millions and millions of miles from the
Sun sunlight strikes a pigment molecule
exciting the pigment molecule exciting
the pigment molecule remember what
sunlight does when it when it strikes
the pigment that pigment
electrons go to a higher energy state
that when the picnic goes back down to
ground energy state this pigment itself
passes on energy it's not passing on
electrons I want to make that very clear
right now okay when sunlight strikes
this pigment this pigment becomes
excited but it doesn't pass an electron
to the next pigment you know what it
passes on to the next pigment this
pigment passes on energy energy to the
next pigment not electrons energy and
when this pigment passes on energy to
this pigment this pigment gets excited
its electrons go to a higher energy
State does that make sense so the light
the photon of light all they had to do
was excite this pigment then on its own
this pigment excited this pigment which
then in turn excites its neighbour which
then in turn excites its neighbour which
then excites its neighbour you see
that's why it's called a light
harvesting complex because here's light
and the power of light gets harvested it
gets passed on until it reaches the
center called the reaction center so the
light gets but that light energy energy
from the light gets passed on and on and
on and on and on until it gets passed to
these two green dots there's always two
green dots in the center those are
called the special pair there's always
two the special pair of chlorophyll a
it's chlorophyll a there's a chlorophyll
a there's a chlorophyll a special pair
of chlorophyll a molecules inside of the
photosystem not only in the photosystem
it's in the blue part called their
reaction center and that's where the
energy goes that's where the energy goes
from the green from the purple parts
okay the energy reaches the special
chlorophyll pair so what does the
special chlorophyll pair do at this
point and why is it so special
here's what it does okay you ready for
this when the special chlorophyll pair
gets excited it not only gets
it passes on electrons did you see that
that the other chlorophyll molecules did
the other pigment molecules pass off
electrons no remember these ones got
excited and passed on energy but once
you reach the special pair the special
pair when they get excited they don't
just pass off energy they actually pass
off their electrons they say here take
my electrons so they actually can become
oxidized right so this becomes oxidized
it it releases its electron so it loses
its electrons it becomes oxidized and it
reduces it gives electrons to it reduces
this box this box represents the primary
electron acceptor okay this is the box
that's going to accept those electrons
it's the primary electron acceptor and
then what happens to those electrons
from this point here's what you need to
know once the primary electron acceptor
this box gets those electrons from the
special pair it can then pass off those
electrons the electrons can then leave
the photosystem altogether they actually
leave the photosystem and go on a
journey somewhere okay so that's how a
photosystem works again photons of light
strike pigment molecules in the light
harvesting complex pigment becomes
excited which then in turn excites its
neighbor that it neighbor is now excited
and it will excite its neighbor which
excites its neighbor which excites its
neighbor which excites its neighbor who
happens to be a special chlorophyll pair
member that special chlorophyll pair
once excited can become oxidized passing
off electrons to the reaction center
complex which becomes reduced and that
complex then passes off the electrons
you know and the electrons can actually
leave the entire Apple they leave the
whole photosystem so knowing that let's
bounce back to this process do you
remember this is the full overview this
is the full overview
of the light reactions of photosynthesis
so let's take a closer look okay look
remember I said the the story begins at
photosystem two and then later on you
have photosystem one I just want to tell
you something before I start explaining
this you see the special Coralville pair
on photosystem two and the special
chlorophyll pair on photosystem one well
what I need you to know is that they
have special names okay look they have
special names let's find those names I
just want to show you look on
photosystem two the special pair is
called P six eighty on photosystem one
the special pair of chlorophyll a is
called P 700 so let me show you here you
see those two chlorophyll molecules
chlorophyll eight those two are called
p680
you see these two over here
those two are called P 700 okay and the
reason for that is that's like the
optimal wavelength of absorbance by
those pair so you don't need to know
that but that's where that name came
from so anyway let's break it down are
you ready this is how the light
reactions of photosynthesis work the
story begins at photosystem two I know
that's weird photosystem two comes first
and then photosystem one comes later you
might be wondering why let me address
that real quick before we start
photosystem one was discovered first and
then photosystem two was discovered
later
hence the weird nomenclature one and two
even though photosystem occurs first in
the process it's called photosystem two
because it was discovered second so you
don't need to know that but just in case
you're curious or confused so again
let's start this process so what is this
membrane this is the thylakoid membrane
the membrane of the pancake stacks
what is this apple structure this is the
photosystem 2
the purple part called the light
harvesting complex and the blue part
called the reaction center the reaction
center has a special pair called p680
member that so here we go
so light from the Sun light strikes this
green dot this pigment molecule that
pigment could be chlorophyll a that
pigment could be chlorophyll be that
pigment could be a xantho silic rotten
oits it doesn't matter it's a pigment in
the light harvesting complexes that
pigment becomes excited remember that
this pigment becomes excited which then
can excite its neighbour which excites
its neighbour which excites its
neighbour which excites its neighbour
which excites its neighbour which is
p680 except speak 680 and what does p680
do that's different it not only excites
its neighbor a instead of exciting its
neighbor it passes electrons you see the
yellow arrows here the yellow arrows
represent electrons actually getting
past so the p680 passes electrons it
becomes oxidized to p680 plus the
electrons hopped to the box the primary
electron acceptor and look the electrons
leave photosystem 2 they go on a journey
you see those electrons go on this long
journey so let's go step by step the
electrons hop to the box the primary
electron acceptor the electrons then
leave the photosystem and they go
through this guy called P Q they go
through this guy this transmembrane
protein complex called cytochrome
complex and then they travel through
this guy called PC and then they end up
here stuck here they stay wait here
they're stuck here on P 700 which is the
central chlorophyll pair on photosystem
1 that's where they kind of get
temporarily stuck so let's talk about
this again light strikes a pigment that
pigment excites its neighbor excites its
neighbor excites its neighbor the
excitement reaches the central
chlorophyll pair which then becomes
oxidized to p680 plus from p680 to p680
plus the electrons go to this box called
the primary election
except er that electrons can then leave
the photosystem to leave go through PQ
cytochrome complex and PC and now
they're stuck on P 700 in photosystem
one so what happened what happened as
the electrons crossed this way what
happened as the electrons crossed PQ
cytochrome complex of PC let's talk
about that again
PQ cytochrome complex of PC this
constitutes what's called a electron
transport chain or etc' what does that
mean
that means that electron spontaneously
moved through the electron transport
chain spontaneously so for free that
releases energy right spontaneous things
release energy so the electrons
traveling through P Q cytochrome complex
a PC releases energy that you could use
to do work what work does it want to do
well cytochrome complex in particular
wants to do something with that energy
it will use that energy to move protons
from the fluid out here called the
stroma stroma it will move protons in to
the space down here called the thylakoid
space you see so now protons have been
actively transported actively
transported against the concentration
gradient now you have a really high
concentration of protons in the
thylakoid space why do we care about
that well guess what those protons want
to go back out into the stroma right if
protons have been actively pumped into
the thylakoid space you know what that
means
that means there's gonna be a lot of
protons in this space and those protons
are gonna want to diffuse right back out
where there's lower relatively lower
proton concentration and again Ken
protons cross directly through the
membrane back out no they need an avenue
and that avenue is provided by this
protein complex which should look
familiar
this protein complex is called ATP
synthase just like the ATP synthase
during cell respiration okay what
happens protons protons diffuse out
diffuse through the ATP am
and when they do that ATP synthase spins
and that allows this part of ATP
synthase to join ADP adenosine
diphosphate with P or P I called
inorganic phosphate when you take
diphosphate and phosphate inorganic
phosphate you make ATP adenosine
triphosphate and that is how you make
ATP and remember this process is called
photo phosphorylation and that ATP can
then go to the Calvin cycle to help with
making sugars okay so that was why the
electrons moving through P Q cytochrome
complex of PC was important because that
electron flow provided the energy to
actively pump protons into the thylakoid
space and those protons chemiosmosis
back out into the stroma through proton
motive force was gave the ATP synthase
the power it needed to spin and produce
ATP through photo phosphorylation okay
and that ATP is a product of the light
reactions of photosynthesis and that ATP
is required for the Calvin cycle okay so
where do we leave off the the electrons
are now stuck on photosystem one the
electrons are now stuck on photosystem
one at this central pair called p700
light now strikes look light strikes
this pigment molecule in the purple part
remember the light harvesting complex a
photosystem one while we're doing this
again light strikes this pigment which
becomes excited which excites this
pigment which excites this neighbour
which excites its neighbor which excites
its neighbor which excites its neighbor
and then the excitement reaches the p700
where these electrons are now waiting
there the electrons that had that had
been waiting here they're waiting here
the excitement from the sunlight reaches
there now that central pair can become
oxidized that central pair passes off
those electrons the electrons can now
leave ship leave the photosystem
and go on a journey through fd2 this
enzyme this is an enzyme called nadp+
reductase this enzyme is not nadp+ this
enzyme is n adp plus reductase it's the
enzyme ace it's the enzyme that reduces
nadp+ okay so those electrons come to
nadp+ reductase those electrons are
given to nadp+ to reduce nadp+ to nadph
so what does this enzyme do it basically
hands those incoming electrons to nadp+
reducing it to NADPH that's how the
NADPH is made during the light reactions
of photosynthesis which go to the calvin
cycle and with the help of ATP and NADPH
from these steps go into the calvin
cycle to make sugars okay now now now
you might you might let's start over
real quick look at this I didn't explain
this part right do you remember what
happened at the beginning light hit this
pigment which excited that pigment which
excited that pigment and then when p680
got excited it got oxidized to p680 plus
and those proton I'm sorry the electrons
went on a journey well guess what now
the p680 is called p680 plus you know
why because it's oxidized the electrons
already went on this journey again and
so that it lost its electrons right so
it needs more electrons the pair needs
more electrons where is it gonna get
more electrons here's how look water is
gonna come along and water is gonna
reload p680 with electrons water will
reduce P six eighty plus back to P six
eighty so that this whole thing that I
just explained can happen again to
reload it to reload it with electrons
right because it lost its electrons you
see so we have to give it more electrons
how do we give it more electrons water
will donate its electrons to the P six
eighty plus so how does that work P six
eighty plus here's what you need to
understand peace
80-plus is a very oxidative source let
me bust out my my little board here give
it a quick little race okay do I have a
thick marker oh I have a thin one I
think you could read this oh okay
look P six eighty plus yeah you can see
that right P six eighty plus is very
very oxidative you know what oxidative
means it has a high pio ratio it has a
high sorry yo ratio yo ratio
it has a very it's very oxidative it's
it's high electronegativity very high
electronegativity so it's so greedy for
electrons P six eighty plus you know
when when P six eighty has lost its
electrons it's so greedy for electrons
its e o prime value is high okay it's a
o is high which means it is super
oxidative it can take electrons from
water okay
it can take electrons from water I'll
say Steel's electrons from water h2o
okay steals electrons from water that's
how greedy it is for water and for
electrons I should say so what is it
what happens when it picks up those
electrons
what does p680 become P six eighty plus
becomes P six eighty again okay now it's
a Oh is lower okay it's a Oh is lower
it's it's reductive reduction potential
is lower it's greediness for electrons
is lower but does that mean it passes
off those electrons take a look take a
look here so
p680 plus is so greedy for electrons
that can steal electrons from water
those electrons those electrons make
p680 plus back to p680 it reduces it
back to p680 but those electrons still
can't leave you know when those
electrons can leave and go on that
journey again only when sunlight
sunlight has to help sunlight hits this
pigment which excites that pigment which
excites this pigment which excites that
pigment which excites that pigment which
excites p680
look p680 had a lower reduction
potential okay
p680 had a lower reduction potential but
p680 plus energy from the Sun Wow that's
a very low eeo very low very low
reduction potential very negative value
for reduction potential and when you
have a negative do value your easily
oxidized the the electrons can go on a
journey so do you see p680 is a very
special little molecule why because it's
like dr. Jekyll and mr. Hyde when it's
missing its electron when the electron
leaves it becomes p680 Plus which is
like one of the strongest oxidizing
agents in the universe okay it's greedy
greedy greedy for electrons but then
once it got those electrons what's it
becomes p680
and especially once it becomes p680 and
receives excitement energy excitement
from the sunlight now it switches from a
very positive eeo value a very positive
reduction potential very positive
electronegativity to very negative
reduction potential very negative zero
value very very negative
electronegativity so it has a very
negative zero value
now the electrons easily leave right the
electrons easily hop to the primary
electron acceptor and go on a journey
right same thing here the electrons
reach P 700 that then they they're stuck
there they're stuck there until sudden
light energy makes its way to P 700 p700
switches to a very negative Zeo value
letting go of those electrons those
electrons go on a journey so what they
say as P 680 is kind of like a reduction
potential switch because you're going
from a very positive yo value to a very
negative EO value at back and forth and
back and forth it's like a switch dr.
Jekyll mr. Hyde dr. Jekyll mr. Hyde very
positive EO value very negative value
that's kind of how this whole process
works and again this is called linear
electron flow of photosynthesis of the
light reactions of photosynthesis
because the electrons start on water
water is the primary electron donor and
the electrons end up on nadp+ to make
NADPH okay and that that's where the
electrons ended up at the end of light
reactions now those electrons are off to
the Calvin cycle to make sugar okay so
again what are the reactants of the
light of the of linear linear electron
flow of photosynthesis the reactants are
sunlight and water and the products are
what the products are NADPH
ATP through photo phosphorylation and
the waste product is oxygen this is why
plants breathe out oxygen and provide
the earth with oxygen and that is the
source of oxygen on the planet that you
and I enjoy okay there are a lot of
slides here in a row see linear electron
flow this is linear electron flow you
can see in linear electron flow you've
got
step one with P six eighty and
photosystem two step two step three step
four Step five okay these are the steps
we talked about in detail just now so
this these slides will help you break
down those concepts again okay this is
the this conceptually what's happening
with those energy states of the
electrons as well so let me take a quick
break when we come back out I'll explain
cyclic electron flow I'll also explain a
little bit about the Calvin cycle which
is how we're actually gonna make sugar
and then we'll wrap up this chapter
alright we're almost through it I hope
you're with me so far
alright I'm gonna grab another tea or
something and you do the same
break time hey everyone welcome back
alright so I told you that I would let
you know what cyclic electron flow means
during photosynthesis let me explain
cyclic electron flow I'll use this image
to explain it remember what linear
electron flow was the electron started
out on water and then they made their
journey through all the way to nadp+
joint the electrons joined up with nadp+
to make an ADP H right that's linear
electron flow so what's cyclic electron
flow it's it's a process that plants can
employ to maximize the use of these
electrons make as much ATP as possible
so let me show you how it works
what's the electrons make their way here
to P 700 what should they do
right normally the sunlight energy
excites these pigments which then excite
Piet 700 and those electrons get passed
on from P 700 and the electrons go this
way right
normally the electrons go to nadp+
reductase right now during cyclic
electron flow which is kind of you can
think of it as a short-circuiting of
this process of photosynthesis the
electrons are actually passed the other
way you see the electrons are passed
through cytochrome complex again back to
PC at
to photosystem 1 so imagine suddenly
hits this pigment in the in the late
harvesting complex of photos is that
what that pigment becomes excited which
excites neighbour which excites its
neighbour which accepts its neighbour
which excites its neighbour which is
Isis neighbour which excites p700 making
it a very negative zo- reduction
potential low low low electronegativity
those electrons leave but instead of
leaving to the right they leave to the
left they go through the electron
transport chain to PCN right back to
p700
to have that happen again sunlight
excites it goes back through peek
through cytochromes complex back to pc
back to p700 sunlight hit energy excites
again it goes back you see this is a
cycle you see this is no longer linear
starting at water and ending up on NADPH
this is a closed loop it's a circle the
electrons go from p700 back through
cytochrome complex back through pc back
to p 700 with the help of sunlight
energy they leave again back through
site o compiled complex back through pc
back to p 700 and again and again and
again so as long as you have sunlight
you can employ cyclic electron flow and
well what's the point of that why would
you want to keep doing this over if why
would a plant want to keep doing this
over and over and over instead of
getting getting through with it getting
to the point which is to make any DPH
why why do this cycle over and over well
what are you producing with this cycle
are you producing NADPH no are you
producing extra oxygen no but what are
you producing you're going through this
electron transport chain over and over
and over you know what that does that
powers the cytochrome complex powers
this pump to pump protons right because
when the electrons flow they flow
spontaneously that provides energy
energy to do something active which is
pump protons so the proton concentration
becomes high here those protons then
want to go back out they do
back out through chemiosmosis inserting
a proton motive force spinning ATP
synthase which produces ATP in the
stroma right that so so cyclic electron
flow this guy you see the string cyclic
I'm sorry him during cyclic electron
flow p700 provides electrons right
because sunlight sunlight hits a pigment
which excites its neighbour which
excites a neighbour which excites a
neighbour which excites p700 SP 700
releases electrons which leaves the
photosystem one goes through cytochrome
complex back to pc back to p 700 over
and over and over again and remember the
only product of cyclic electron flow is
ATP not oxygen not NADPH during cyclic
electron flow it's kind of a
short-circuiting of the system you're
only producing ATP okay so that's the
point of cyclic electron flow now one
one more thing that you should really
understand that you should really take
note of and understand for exam results
is the difference between what's going
on in the mitochondria during cellular
respiration versus what's going on in
the chloroplasts during photosynthesis
okay what's happening in each keep in
mind both of them have an area with high
proton concentration an area that a
membrane both of them have a special
membrane that has an electron transport
chain and ATP synthase and both of them
have an area where ATP is actually made
so you should know that for example
where's the proton concentration high in
the mitochondria it's high in the
intermembrane space where's the proton
concentration high in the chloroplast
it's high in the thylakoid space see
this is kind of a cheat sheet see the
proton concentration in the mitochondria
is high in the intermembrane space the
proton concentration is high in the
I'll annoyed space of the car applause
what about in the mitochondria where's
the ATP synthase found to the
mitochondria and the et Cie they're
found in the inner membrane not the
outer membrane the inner membrane right
what about the chloroplasts where's the
EGC and ATP synthase found remember it's
in the thylakoid membrane it's in the
pancake stack memory right there
okay and then in both of them where's
the ATP actually made where's the ATP
actually made in the mitochondria it's
made in the fluid in here this is called
the matrix right it's made here in the
chloroplast it's made in the stroma over
here okay that's where the ATP is made
so just know that remember and the ATP
made to the mitochondria is made by
oxidative phosphorylation and the ATP
made in the chloroplast is made by photo
phosphorylation okay so just know that
be able to juxtapose the two compare and
contrast okay because it's very similar
they both involved proton concentration
ATP synthesis
ATP synthase electron transport chain
they're very very similar processes
they're just converse reactions right so
what else the last thing we need to talk
about is this remember let me jump to
the beginning real quick okay we just
talked about linear electron flow how
the products are oxygen ATP and NADPH it
required light and water water was the
primary electron donor the first
electron donor and what did we again
what did we produce ATP and NADPH which
needs to feed into part two the Calvin
cycle where does the Calvin cycle happen
where does part two of photosynthesis
happen it happens in the fluid look it's
the fluid outside of the pancake stacks
this is the stroma photosynthesis Calvin
cycle happens in the stroma okay and
look what are we required we require co2
for calvin cycle as a reactant we also
require ATP from the light reactions
NADPH from the light reactions remember
that's the source of our HS and sugar
so again what are we about to do
remember we're trying to make sugar
which is C's HSN those the C's that the
O's come from co2 the HS come from and
Adi pH there's your H right there so we
have to give these nature's to co2 which
is going to convert our NADPH and
oxidize it back to edit EB plus and
that's not a free thing to do that's
actually difficult to do so ATP isn't
gonna allow us to do that until we've
got sugars made so let's talk about the
Calvin cycle which happens in the stroma
let's talk about that okay so Calvin
cycle what you need to understand about
the calvin cycle is that there are three
main phases to the calvin cycle you need
to understand the first phase is called
carbon fixation and the enzyme
responsible for carbon fixation is
Rubisco then phase 2 is called reduction
and phase 3 is regeneration of the co2
acceptor ribulose bisphosphate or rubp
let me break that down for you this is
what the calvin cycle looks like again
the calvin cycle occurs in the stroma of
the chloroplast and it's a cycle I'll
explain why it's a cycle in a minute see
what feeds into the cycle co2 3 co2 co2
they enter one at a time each co2 enters
one at a time so you're seeing what
happens to one co2 alright
actually you're seeing what happens to
all three but just know that they feed
in one at a time
now before you start panicking you don't
need to know every single step of the
calvin cycle and what happens during
every little step so don't panic instead
focus on what I'm about to say these are
the important things to understand co2
comes into the cycle Rubisco Rubisco is
the enzyme that captures the co2 and
does a process called carbon fixation
phase one is called carbon fixation the
enzyme that catalyzes that reaction the
enzyme that makes that
it is called the Rubisco what does
carbon fixation mean here's what it
means okay carbon fixation means taking
carbon from a gas form like co2 taking
co2 from gas form and making it into
solid form how do you do that how do you
make carbon and get from a gas to a
solid here's how here's what this enzyme
is doing here's what we're Bisco is
doing are you ready you see this
molecule right here that I'm
highlighting or circling this molecule
is an organic molecule it's a carbon
containing solid called rubp or ribulose
bisphosphate you see it's got one two
three four five carbons in it two
phosphate groups that's why it's called
bisphosphate two phosphate groups anyway
this organic molecule is a solid right
it's not a gas it's a solid it's called
rubp ribulose bisphosphate also known as
the co2 acceptor rubp is the co2
acceptor so what is it going to do it's
going to accept co2 what does that mean
Robus go the enzyme take co2 and sticks
it on to our ubp you see this you see
this one two three four five six carbons
now on rubp so you take this you stick a
carbon dioxide on to the second carbon
okay
and then this is very unstable molecule
which breaks down into these
phosphoglycerate molecules three carbon
molecules all right again you don't need
to know these little baby steps but I'm
just telling you what's happening you're
taking a solid called rubp it's the co2
acceptor rooibos co the enzyme attaches
co2 to the acceptor and now co2 is fixed
this is what carbon fixation means
taking co2 carbonate from a gas state to
a solid state this this molecule breaks
down into phosphoglycerate and then
guess what what are we going to do at
this point
what have we captured have we made sugar
yet no all
we've done is got C's and O's for our
sugar you don't remember what sugar is
C's HS and O's we've now captured season
O's to make sugar and look with the help
of ATP with the help of ATP we are going
to use our NADPH and we're gonna hand
those H's we're gonna hand those H's to
the season O's to the carbon dioxide
that we captured basically and that
process is called reduction you remember
what reduction means gaining of
electrons if we take our C's and our O's
and we reduce it that means we're giving
it those electrons we're giving it those
ages from NADPH and that's not free it's
not easy to do so ATP is required from
the light reactions you see that so now
we have what we've given the h's from
NADPH with the help of ATP we've given
those ages to the co2 we captured so now
we have sugars we've made sugars we've
made sugars which are ultimately going
to become the six carbon sugar glucose
and other organic compounds yay that we
did it we got C's HS and O's we got our
season arose from the air from co2
through carbon fixation we then handed
it a bunch of H's from NADPH with the
help of ATP now we have C's ages and O's
boom we got sugars and other organic
molecules awesome right so that's phase
one taking co2 out of the air
phase two giving it H's our electrons to
make sugar now we've got our sugar but
we still have to close this loop we
sought to finish this cycle so what's
the last thing we have to do part three
phase three is called
regeneration of the co2 acceptor rubp do
you see this molecule right here do you
see this molecule right here this is
called
rubp ribulose bisphosphate we just
talked about it it's the molecule that's
going to accept this incoming co2 it's
gonna accept that co2 through carbon
fixation you have to make some more of
this so that you could keep the cycle
going at the end of the cycle you have
to regenerate this guy rubp ribulose
phosphates so the Rubisco enzyme can
hand it another co2 and you can do this
process over again so again this process
could consists of three phases carbon
fixation which is catalyzed by the
enzyme rubisco to Ixia two out of thin
air out of gas state and actually
attaches it to this ribulose
bisphosphate this carbon dioxide
acceptor and then with the help of ATP
and nadph that carbon dioxide is then
reduced to sugar and of course we have
to regenerate our rubp ribulose
bisphosphate to keep the cycle going
okay and that's all there is to it
really now you see why we required ATP
and NADPH from the earlier steps because
we're going to use them to reduce the
co2 in the ladder steps and remember
this ATP was made by
photophosphorylation during the light
reactions of photosynthesis do you guys
remember where did this H come from
where did these electrons come from on
the NADPH originally where did they
where did they come from
from water remember we took the H's from
water the oxygen released us that the
water's oxygen released as o2 so the
electrons came from water originally the
electrons went to nad p post if I get
adv H and here those electrons are going
to that co2 to make sugars so think
about it the electrons in photosynthesis
the electrons started on water
they went to NADPH and then they went to
co2 to make C's HSN O's to make sugars
so co2 co2 is reduced that gains
electrons co2 is reduced to sugar water
we took its electrons away water was
oxidized to oxygen and so it's beautiful
process
it's the converse reaction to cellular
respiration and it's the entire reason
you and I are alive and that we have
oxygen to breathe we have calories to
eat a drink and that week
live in a planet that's not overrun by
co2 so thank you plants thank you
photosynthesizers and thank you guys for
watching and learning about the
importance of photosynthesis so with
that I'm going to wrap up this this
chapter and this concept I hope you
learned something all right feel free to
ask questions and I'll catch you guys
next time
