Section 1 : PHOTOSYNTHESIS Part 1
Summary
TLDRThis educational video script delves into the process of photosynthesis, focusing on its two main phases: light-dependent reactions and light-independent reactions. It explains how plants and certain other organisms convert light energy into chemical energy, producing glucose and oxygen. The script details the role of chloroplasts, thylakoids, and the electron transport chain, highlighting the production of ATP and NADPH in the light-dependent phase. It also touches on cyclic and noncyclic photophosphorylation, emphasizing the importance of these processes for generating energy-rich molecules necessary for plant growth.
Takeaways
- đż Photosynthesis is the process by which green plants, some algae, and certain bacteria convert light energy into chemical energy, producing glucose and oxygen.
- đ The process is divided into two main phases: light-dependent reactions and light-independent reactions (Calvin cycle).
- đ± Light-dependent reactions occur in the thylakoid membranes of chloroplasts and involve the production of ATP and NADPH.
- đ§ Photolysis, the splitting of water molecules, provides electrons and protons for the light-dependent reactions and releases oxygen as a byproduct.
- đ Electron transport chains transfer excited electrons through a series of proteins, pumping protons into the thylakoid space to create a concentration gradient.
- đ Chemiosmosis uses the proton gradient to generate ATP by allowing protons to flow back into the stroma through ATP synthase.
- đ Cyclic and non-cyclic photophosphorylation are two types of electron transport processes; cyclic does not produce NADPH or oxygen, while non-cyclic does.
- đ The Calvin cycle, occurring in the stroma of chloroplasts, uses ATP and NADPH to fix carbon dioxide into glucose.
- đ± Chloroplasts are the organelles in plant cells where photosynthesis takes place, containing thylakoids and stroma.
- đŹ Photosystems I and II are key components of the light-dependent reactions, with PSII initiating the process by absorbing light and splitting water.
Q & A
What is photosynthesis and how does it relate to cellular respiration?
-Photosynthesis is a process where green plants, some algae, and certain bacteria convert light energy into chemical energy by using carbon dioxide and water to produce glucose and oxygen. It is the reverse of cellular respiration, where organisms convert glucose and oxygen into carbon dioxide, water, and energy.
How is light energy converted into chemical energy during photosynthesis?
-Light energy is converted into chemical energy through two main phases of photosynthesis: the light-dependent reactions and the light-independent reactions (Calvin cycle). In the light-dependent reactions, light energy excites electrons which are then used to produce ATP and NADPH. These energy-rich molecules are then used in the Calvin cycle to fix carbon dioxide into glucose.
What are the two phases of photosynthesis and what happens in each?
-The two phases of photosynthesis are the light-dependent reactions and the light-independent reactions (Calvin cycle). The light-dependent reactions occur in the thylakoid membranes of the chloroplast and involve the production of ATP and NADPH using light energy. The light-independent reactions take place in the stroma of the chloroplast and use ATP and NADPH to convert carbon dioxide into glucose.
What are the roles of chloroplasts in photosynthesis?
-Chloroplasts are the organelles in plant cells where photosynthesis takes place. They contain pigments like chlorophyll that absorb light energy and use it to power the light-dependent reactions. The chloroplast has a double membrane structure with thylakoids (stacked as grana) where light-dependent reactions occur, and stroma where light-independent reactions take place.
What are the two types of photosystems involved in photosynthesis and what is their function?
-There are two types of photosystems involved in photosynthesis: Photosystem I and Photosystem II. Photosystem II absorbs light at around 680 nanometers and uses it to split water molecules, releasing oxygen and electrons. Photosystem I absorbs light at around 700 nanometers and uses the excited electrons from Photosystem II to produce ATP and NADPH.
How does the splitting of water molecules contribute to photosynthesis?
-The splitting of water molecules, also known as photolysis, occurs in the light-dependent reactions of photosynthesis. It provides electrons that are used to generate ATP and NADPH, and it also releases oxygen as a byproduct.
What is the role of ATP and NADPH in the second phase of photosynthesis?
-ATP and NADPH, produced in the light-dependent reactions, are used in the light-independent reactions (Calvin cycle) to power the conversion of carbon dioxide into glucose. ATP provides the energy, and NADPH provides the reducing power necessary for this process.
What is chemiosmosis and how does it relate to ATP production in photosynthesis?
-Chemiosmosis is the movement of protons (H+) across a membrane, driven by a concentration gradient, which is used to generate ATP. In photosynthesis, a proton gradient is created across the thylakoid membrane during the electron transport chain, and the flow of protons back into the thylakoid space through ATP synthase drives the synthesis of ATP from ADP.
What are the differences between cyclic and noncyclic photophosphorylation?
-Cyclic photophosphorylation involves only Photosystem I and results in the production of ATP without the production of NADPH or the release of oxygen. Noncyclic photophosphorylation involves both Photosystems I and II, leads to the production of both ATP and NADPH, and includes the photolysis of water, releasing oxygen as a byproduct.
Why do cells perform cyclic photophosphorylation?
-Cells perform cyclic photophosphorylation to generate additional ATP when the demand for ATP is high and the need for NADPH is low. This process does not produce NADPH and is more efficient for ATP production.
Outlines
đż Introduction to Photosynthesis
This paragraph introduces the topic of photosynthesis, explaining it as the process by which green plants produce their own food using carbon dioxide and water in the presence of sunlight. The process is divided into two parts: Part One discusses the light-dependent reactions that occur in chloroplasts, while Part Two, to be covered in a subsequent video, will delve into the light-independent reactions. The paragraph emphasizes the importance of understanding key concepts for exams rather than getting into intricate details. It also mentions that photosynthesis is not exclusive to plants but is also performed by certain algae and bacteria, highlighting the broader scope of this biological process.
đŹ The Mechanism of Photosynthesis
This section delves into the specifics of photosynthesis, focusing on the light-dependent reactions that take place in the chloroplasts. It describes the structure of chloroplasts, including the thylakoid membranes where the light-dependent reactions occur, and the stroma where the light-independent reactions occur. The paragraph explains the role of photosystems, particularly Photosystem II, in the initial stages of electron transport. It details how light energy is absorbed, leading to the excitation of electrons and the subsequent splitting of water molecules into protons (H+) and oxygen. The paragraph also discusses the production of ATP and NADPH, which are essential for the subsequent phase of photosynthesis, and the process of chemiosmosis that leads to ATP synthesis.
đ Phosphorylation in Photosynthesis
The final paragraph discusses the two types of phosphorylation in photosynthesis: cyclic and noncyclic. It explains that cyclic phosphorylation involves only Photosystem I and does not require water or produce oxygen or NADPH, but it generates additional ATP. Noncyclic phosphorylation, on the other hand, involves both photosystems and includes the splitting of water, leading to the production of oxygen, ATP, and NADPH. The paragraph concludes with a question to test the viewer's understanding of cyclic phosphorylation, highlighting that photoactivated electrons return to Photosystem I after passing through the electron transport chain, which is characteristic of the cyclic process.
Mindmap
Keywords
đĄPhotosynthesis
đĄAutotrophs
đĄLight-dependent reactions
đĄChloroplasts
đĄThylakoids
đĄStroma
đĄPhotosystems
đĄElectron transport chain
đĄChemiosmosis
đĄCyclic and noncyclic photophosphorylation
Highlights
Photosynthesis is a process where green plants make their own food using carbon dioxide and water in the presence of sunlight.
The process of photosynthesis is divided into two phases: light-dependent reactions and light-independent reactions.
Light-dependent reactions occur in the chloroplasts and produce ATP and NADPH.
Light-independent reactions use ATP and NADPH to produce glucose.
Chloroplasts are double membrane structures that capture light energy for photosynthesis.
Thylakoids are the sites of light-dependent reactions within the chloroplasts.
Stroma is the fluid-filled space in chloroplasts where light-independent reactions take place.
Photosystems are pigments that absorb light of different wavelengths, with two types: Photosystem I and Photosystem II.
In phase one, electrons are activated by light and move through an electron transport chain.
Water molecules are split into H+ ions and oxygen during light-dependent reactions.
ATP is produced by chemiosmosis, which uses the H+ gradient created by the electron transport chain.
NADPH is produced when electrons are transferred to NADP+ during light-dependent reactions.
Cyclic and noncyclic photophosphorylation are two types of processes that generate ATP.
Cyclic photophosphorylation only involves Photosystem I and does not produce NADPH or oxygen.
Noncyclic photophosphorylation involves both photosystems and includes the splitting of water, producing oxygen.
Cells choose between cyclic and noncyclic photophosphorylation based on their ATP and NADPH requirements.
The video concludes with a question about cyclic photophosphorylation, highlighting that photoactivated electrons return to Photosystem I.
Transcripts
hello everyone and welcome to the next
video for the same section that we are
discussing and the same subsection which
is biochemistry in the last video we
discussed about cellular respiration in
this video we will be discussing about
the process of photosynthesis and this
uh particular topic will be dealt in two
videos so this is a part one of the
video and another video we will discuss
part two photosynthesis because it's a
pretty big topic okay but as you know we
are just discussing the key concept
whatever you need to remember for the
exam you're not going to go into the
details of
anything okay so coming to
photosynthesis photosynthesis is a
process in which the plants the green
plants make their own food by taking
carbon dioxide and water in the presence
of sunlight they make the food in the
form of glucose and they liberate oxygen
that you breathe in so in this process
you're actually converting light energy
into chemical energy and and you as you
know this is usually done by autot
tropes autot tropes are organisms that
can make their own food like plants but
please remember photosynthesis is also
carried out by some algae and some
bacteria so plants are the not not the
only one who do photosynthesis okay
there are other organisms on this Earth
who do that anyways so the
photosynthesis the whole process can be
divided into two phases phase one are
light dependent reactions the depend on
light okay so this these particular
reactions they take place in organal
called chloroplast we'll discuss that in
a little bit detail after a few slides
and what is the phase one doing the
light dependent reactions they make ATP
and nadph molecules and these ATP and
nadh nadph molecules that you make in
phase one which is the light dependent
reactions you use them in phase two to
make your final product which is glucose
so again phase one light dependent
reaction you make ATP and nadph phase
two light independent reactions you make
use of that ATP and nadph which you made
in Phase One to make the final product
which is glucose now the next thing is
you have to know some components of
chloroplast chloroplast the whole
function of it is to capture the light
energy which is sunlight and to use it
for making uh food for the plant now the
chloroplast is a double membrane
structure you have an outer membrane and
you have an inner membrane inside the
chloroplast you see these stack of these
coins first each coin is called a thilo
covid and together the stack of coins is
called a granum plural is Gran sometimes
you will see the word Grana Grana means
more than one granum okay so each is a
granum together they are the
Grana now there's something else the
fluid fills space here inside the
chloroplast we call that stroma so
please remember that thids
are where your light dependent reaction
takes place and your light independent
reaction takes place in the stroma so
phase one in the piloid phase two in
stroma this is an important concept
please make make sure you know it now
going into the details of phase one so
we the phase one the first part of phase
one is electron
transport so here what happens look what
happens in here so before we go into
that there is something that something
else that you should know in
photosynthesis we talk about something
called a photos system okay so photos
systems are nothing but they contain
pigments that absorb lights of different
wavelength so there are two photosystems
in photosynthesis you have photosystem
one and photos system 2 so photos system
one absorbs light at around 700
nanometers photosystem 2 absorbs light
at around 680
nanometers so here when you talk about
phase one we don't talk about whour
photosystem first one first we talk
about photo system 2 so we start from
photo system 2 here and I will show you
why because there are two types of uh
phosphorilation we'll go to the cyclic
and acyclic in in a bit but right now
let's focus on the electron transport
chain then we'll move on to that concept
also later on okay so here this is a
sunlight and this is your photo system
to the green things so what happens
first the light is absorbed bi your
photos system because they contain
chlorophyll so when light is absorbed
absorbed they they excite the electrons
so when the electrons are excited or
activated look what is happening a water
molecule is splitting into two H+ ions
and half oxygen
molecule okay now so and then what is
happening this this the two H+ ions that
you are making they stay in the thilo
covid space
okay and the oxygen that you're making
is a waste product remember what does
the photosynthesis do it takes carbon
dioxide and it takes water and it makes
oxygen as a product and it also makes
glucose that will be seen in the next
phase not now the final product glucose
you will get not after phase one you'll
get after phase two okay now what
happens
next now the electrons which are
activated they go on moving between one
electron acceptor to the other okay and
then finally so they go on you know from
one electron acceptor to the other
electron acceptor and when they are
doing that when they are doing that the
protons or the H+ are continuously
pumped inside the thilo covid space this
space okay so finally the electrons go
on uh from one electron accept this is
electron transport chain the electron is
transporting from one to the other to
the other to the other and finally they
come to the electron acceptor called
ferrodoxin ferrodoxin you is present in
photosystem one like the photos system
one transfers the electrons to the you
can say it's almost the um the last in
the series here so the ferrodoxin takes
the electron from photosystem one and
then it transfers this electron to a
molecule called
nadp+ okay which along with the proton
which is present here in this space it
makes something called nadph Remember
after phase one we make two components
we make ATP and we make nadph this is
where where you make nadph now it's turn
for you to make ATP okay how do you make
ATP this is done by a process called
chemiosmosis so what is actually
happening look at this
picture so you when I said when that
when you're splitting water you are
continuously having H+ inside the thilo
covid right inside the thilo covid space
so here in the electron transport chain
this H+ is released outside this this
phas so you have H+ here and you have H+
outside too this creates a concentration
gradient so there are more H+ inside the
thilo covid space than it is outside so
what do you think will happen so so
things always move from a region of high
concentration to a region of low
concentration so your H+ will now start
moving from the thilo covid space
outside okay here outside so how do it
move so look at this this is something
this is something which is called an ATP
synthes it's an
enzyme okay so how does the proton or
the H+ moves it moves through these
channels these enzymes so when the H+
moves through this ATP synthes they
start making ATP so from ADP this enzyme
can make ATP by making use of H+ so now
this is how you make ATP and you make
nadph from phase one look this is the
whole process again so here when light
energy entails photosystem 2 the
electron get activated the water
molecule splits up into two uh protons
and half molecule of oxygen this oxygen
is used uh is released as a waste
product this H+ stays here and then this
electron gets transferred from one
electron area to the other when it does
it starts pumping your H+ also outside
okay so you have H+ inside you have H+
outside now this electron gets carried
from photosystem to to photosystem one
and finally it goes on to something
called ferrodoxin which is the final
electron acceptor ferrodoxin then
transfers this electron to
nadp+ with a proton um um ion together
they make something called nadph and the
H+ inside since H+ is more inside the
piloid space so they want to go outside
to a region of low con uh low
concentration they do that with the help
of ATP synthes which is an
enzyme what does it do it it takes the
H+ or the proton from inside the thid
sprays to outside and when this happens
ADP gets transferred to ATP so these are
your products after your first phase
which is nadph and ATP now the second
phase is when you use this ATP and nadph
to make your final product which is
glucose that will be discussed in the
next video before that you have to know
something called the phosphorilation
there's two type one is cyclic and one
is
noncyclic cyclic means that something
which starts from somewhere and it goes
back this is like a cycle in the cyclic
phosphorilation we just make use of
photo system one there is no photo
system two so you have light and then
you know how look how the electron is
being transferred you start from photos
system one and you go back to photos
system one but when you talk about
non-cyclic phosphorilation so what both
the photosystems are involved
okay so basically you start from photos
system 2 which we just discussed and
then you go to photo system one so the
example that we discussed right now is
was of non-cyclic phosphorilation okay
so here please look here carefully in
cyclic only photosystem one is involved
in for noncyclic both are involved in
cyclic water is not required but
noncyclic we just studied we do the
splitting of water which is photolysis
okay in cyclic phosphorilation oxygen is
not involved in or noncyclic we just saw
oxygen is is involved as the waste
product cyclic phosphorilation you don't
make nadph but in non-cyclic we just
made nadph remember and then the last
one is not very important so here why do
the cells have to do cyclic
phosphorilation then just to make
additional ATP why do cells do noncyclic
so that you get get ATP and nadph for
phase two of photosynthesis that's a
purpose so depending upon what the cell
needs they will either go for the cyclic
or they will go for the non-cyclic F
phosphorilation finally we will discuss
one question and we'll end this video so
this question says which of the
following is true about cyclic
phosphorilation first of all let's see
lost electrons from photos system 2 are
replaced by electron from photo system
one we just said that in in the cyclic
one only photo system one is involved so
there is no way you will have photo
system to here so this option is wrong
look at the next option NAD pH and H+
are produced so in cyclic we do not make
nadph it is not synthesized so your
option two is also wrong look at option
D now photolysis of water molecules
releases the electrons blah blah blah
but we know that in cyclic
phosphorilation we don't use water at
all so we also know if you know about
cyclic phosphorilation you know that
option D is also wrong so the only
option which is suitable here is number
c which is photoactivated electrons pass
along the electron transfer chain before
returning to photo system one returning
means it's a cycle this itself will tell
you something is returning back when
something is Cy click something has to
return back okay so your option is
option C that's your correct answer with
this we end this video thank you so much
for
watching
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