okay everyone i'm going to try something
different for the photosynthesis
information and how i
present that to you and i want to do
that with
a powerpoint like i normally would in a
face-to-face class. so first i want to
show you
the overall equation
for photosynthesis. and i want to make it
clear that this is the
overall equation for photosynthesis.
one of the problems that occurred on the
last
quiz was that on the
take-home part when i asked you
for the equations for the different
stages of cellular or aerobic
respiration. some of 
you only gave me the overall equation
and that's why some of you only got
two points for that particular answer.
but anyway so now you know plus i
added back seven points which is
a lot. so what we have here is
photosynthesis.
now you might wonder why the book starts
with photosynthesis
and other lecturers start with
photosynthesis and i
started with cellular respiration and
fermentation.
and i do that because
basically to me it's easier to explain
cellular respiration than it is to
explain
photosynthesis.  but the issue with that
is photosynthesis comes first. we are
looking at one of those
overall outcomes of the course
where we're looking at energy transfer.
remember
the first law of thermodynamics tells us
that energy is not created or destroyed
only converted from one form to another
and the second law tells us that during
those energy transfers
some or all even of that energy is
converted from
a more ordered form to a less ordered
form
and again heat is going to be the
manifestation
of the second law of thermodynamics.
oops okay so
this is a transfer of energy. sunlight
energy.
into chemical potential energy
in glucose. so we have the sun
that is the ultimate source of our
biological
energy and basically
the the sun has these photons
and there's energy involved or the
sunlight
does it's it's energy basically and
there's this really
amazing electromagnetic spectrum
that is from the sun.
but notice that only this small
small amount is visible light
and that's what we're looking at for
photosynthesis,
is this small amount of visible light
not these wavelengths not these
wavelengths but this
small amount here
of the emissions from the sun.
some of you ask about the primary
producer producers
or the photosynthetic autotrophs
so plants almost every plant
is a photosynthetic autotroph.
there are a couple of truly
parasitic plants that are not
photo-
synthetic like one is called dodder, if
you wanted to look that up it's kind of
interesting.
then there are some protists.  someone
asked about the percentage
of the protists that are photosynthetic
and i just don't have that answer.
i did a quick google search last night
and couldn't find anything.
and then some prokaryotes.
most of the prokaryotes are not
photosynthetic
autotrophs. so basically this
is a prokaryote, Anabaena,
that is uh photosynthetic.   this is a mat
of
algae scum in a pond
so that would represent our protist. and
i have an aquatic plant here
that we sometimes use in fact for
labs which is called Elodia.
so in the eukaryotic
primary producers, the chloroplasts are
the sites of
photosynthesis. now of course prokaryotes
do not have chloroplasts. i don't think
that shows up that well
prokaryotes do not have
the uh chloroplast
but they do have some end foldings
of their cell membranes that set up
a place for the membrane gradient
that to be achieved that is part
of the light independent reactions.
are like dependent excuse me light
dependent reactions.
all right we're still in a little bit of
background here where there are quite a
few different plant pigments
anything that gives color to a plant is
one of its pigments
but chlorophyll a and chlorophyll
b are the
the most common of the photosynthetic
pigments. prokaryotes and
protists might have something different
than um
than the uh sorry i was
distracted by the light on the camera
okay
so let me start over.
prokaryotes may have something
different or they do have something
different than chlorophyll.
most of the photosynthetic pigment uh
protists do
as well when i talk about chlorophyll
i'm talking specifically about
plants and one group of
green algae which would be the closest
relative to the plants within the
protists. you don't have to know all that.
what you need to know is we have
chlorophyll a
and b notice there are two peaks there's
one
over here in the violet
in blue and a peak over here well each
of them has a peak so chlorophyll a
chlorophyll b
and then chlorophyll a chlorophyll b
over here
in the reds so these are
absorption spectra. so this is
the ability of the chlorophyll to
absorb the plant pigments and excuse me
the sun's
rays not the plant pigments.   it's the
ability
of the chlorophyll or other pigments as
you can see here there's a couple of
others that are listed
to absorb sunlight energy
and chlorophyll a and b
do not absorb light in the green
visible part or the green part of the
visible
spectrum and that is because
it reflects green and that's why we see
green.
when we look at a plant leaf
the chlorophyll does not absorb
light in the green part of the spectrum
instead it reflects it that's an
important thing to remember.
okay so if we look at
this leaf here it's a cut
section of a leaf and there's an upper
epidermis and a lower epidermis
and the cells are even arranged
differently look how closely packed the
cells are
in the up closer to the upper epidermis
while those that are close to the lower
epidermis
are more randomly placed and there's
more space.
that's intentional or that's an
adaptation not intentional it's an
adaptation
that allows for in the spaces
for gases to uh
be-- for example for the oxygen
that is being produced to move out of
the
leaf through what we call stomata
and the CO2 that's
needed for photosynthesis
to move into the
leaves so that photosynthesis can occur
specifically then in the plants and this
is where we're going to focus.
photosynthesis occurs within the
chloroplast.
i've asked you to be able to draw and
label a
chloroplast and what we have here is an
outer membrane and an
inner membrane okay so the outer ones
here. the inner ones here this one's
labeled
fairly well i like this so
it's a double membrane bound organelle.
then we have these stacks of what look
like
green coins and each of the
quote-unquote coins would be considered
a
thylakoid and this is actually where
photosynthesis takes place in
the thylakoid so each of these
little coin looking structures
and it's across that membrane that we
have
not one but two electron transport
systems or
chains. then there's the liquid matrix
that's called the stroma and that is
where we find
the
calvin cycle the light
independent part of photosynthesis.
now there is one more thing a stack
of thylakoids is called a granum
plural that would be grana. so there were
five
parts outer membrane
inner membrane thalakoid
granum and stroma that i wanted you to
be able to draw
and label.
this summarizes photosynthesis again
so we have an input of light
water and carbon dioxide
from that we get oxygen
and a sugar and a sugar so that's what
we get.  now
notice that we have the light reactions
and the calvin cycle
and this is tying these two together.  the
light reactions
that's where the sunlight is necessary
and
what happens is water is split in
the light reactions releasing
oxygen and providing the electrons
and the hydrogen ions for the electron
transport systems
that allow for and i don't know if you
can see this very well
the production of ATP and
NADPH that
go to the calvin cycle and this is where
the CO2 is also
substrate and then we have our
sugar production.   notice that NADP+
 and ATP +
p then recycle into
the light dependent reactions.
i'm going to talk more about that so
it'll make more sense.
so the light dependent reactions
it's basically about light absorption
uh electron excitement electron
transfer and then ATP production and NADP+
reduction to NADPH
so this looks scary and i'm not asking
you to draw this or memorize
all this. what i want you to see is that
there are two photo systems, photo system
two
photo system one so this is actually the
photo system and this is the electron
transport system that's associated with
photo system two
did i call it photo system one it's
photo system two.
photo system one is here notice with
each of these we have the light
absorption in the form of the photons
of light and then the electron transport
chains or systems and then oh ATP
synthase ,our old friend ATp synthase
from
cellular respiration.   so
notice that photosystem
2 comes first you might wonder why
if this is going this way this direction
well i have an answer it's because
photosystem one was discovered first
there you go. now
what is gonna happen is light is going
to
be absorbed by photosystem ii
excite electrons eventually
a couple of special electrons are going
to be
removed they're going to be so excited
they're going to
jump off and into the electron transport
chain
what that will do then as the electrons
move through
is provide the energy to pump the
hydrogen ions
into the thylakoid inside
the space of the thalakoid.
now as the electrons move through they
lose energy
so when they get to photosystem one oh
some more light oh energized again
electrons
getting energized passing that energy on
until
two special ones hop out
into the electron transport chain and
move
through that electron transport chain.
notice then more
pumping of hydrogen ions and then we
have ATP
synthase with that potential energy
here due to the increased hydrogen ions
inside here relative to outside here
they come
providing the free energy that's needed
to add that
third phosphate group to
ADP producing ATP
then those hydrogens
um and the electrons that have come
through this through photosystem one
attach or reduce NADP+
to NADPH and those are our two big
products or two of our big products
