Photosynthesis - Light Dependent Reactions and the Calvin Cycle
Summary
TLDRThis educational video delves into photosynthesis, explaining it as the process where plants convert light energy into chemical energy. It outlines the light-dependent reactions occurring in the chloroplast's thylakoids, where water is split to produce oxygen and electrons, leading to ATP and NADPH formation. The light-independent reactions, or Calvin cycle, take place in the stroma, fixing carbon dioxide into glucose. The video highlights the role of chlorophyll in light absorption and the significance of the electron transport chain, emphasizing the interplay between photosynthesis and cellular respiration.
Takeaways
- 🌞 Photosynthesis uses light energy to convert water and carbon dioxide into carbohydrates, specifically glucose, with oxygen as a byproduct.
- 🪴 Water is absorbed through the roots, while carbon dioxide enters the leaves through stomata, and oxygen is released through the same openings.
- 🍃 The chloroplast is the organelle responsible for photosynthesis, while the mitochondria handle cellular respiration.
- 🌱 Photosynthesis and cellular respiration are opposite processes: photosynthesis builds glucose and oxygen, while respiration breaks down glucose and oxygen into carbon dioxide and water.
- 🌈 Chlorophyll, the pigment in the chloroplast, absorbs blue and red light but reflects green light, giving plants their green color.
- 🔆 Photosynthesis consists of two stages: light-dependent reactions (in the thylakoids) and light-independent reactions (Calvin cycle in the stroma).
- ⚡ Light-dependent reactions produce oxygen, ATP, and NADPH by oxidizing water and using sunlight energy.
- 🌀 The Calvin cycle converts carbon dioxide into glucose using ATP and NADPH, with NADPH being oxidized back to NADP+.
- 🔋 The products of light-dependent reactions fuel the Calvin cycle, enabling the reduction of CO2 into sugars.
- 🔗 The electron transport chain in the thylakoid membrane generates a proton gradient, driving ATP synthesis through chemiosmosis.
Q & A
What is the meaning of the word 'photosynthesis'?
-Photosynthesis is derived from the Greek words 'photo' meaning light, and 'synthesis' meaning to build. It refers to the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.
What are the net reactants and products of photosynthesis?
-The net reactants in photosynthesis are six water molecules (H2O) and six carbon dioxide molecules (CO2), and the products are glucose (C6H12O6) and oxygen gas (O2).
How do plants intake water and carbon dioxide, and release oxygen during photosynthesis?
-Water is taken up by the roots from the soil, while carbon dioxide enters through the stomata in the leaves. Oxygen is released back into the atmosphere through the same stomata.
What is the role of chloroplasts in photosynthesis?
-Chloroplasts are the organelles within plant cells that carry out photosynthesis. They contain chlorophyll, which is essential for capturing light energy.
How are photosynthesis and cellular respiration different?
-Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy, whereas cellular respiration converts glucose and oxygen back into carbon dioxide and water, releasing energy in the process.
What is the function of chlorophyll in photosynthesis?
-Chlorophyll is the pigment that absorbs light energy, particularly in the blue and red parts of the spectrum, and is essential for the light-dependent reactions of photosynthesis.
Why do most plants appear green?
-Most plants appear green because chlorophyll reflects green light while absorbing blue and red light, which is why the green light is seen by our eyes.
What are the two stages of photosynthesis?
-The two stages of photosynthesis are the light-dependent reactions, which occur in the thylakoids and involve the conversion of light energy into chemical energy, and the light-independent reactions, also known as the Calvin cycle, which occur in the stroma and involve the fixation of carbon dioxide into glucose.
What happens during the light-dependent reactions of photosynthesis?
-During the light-dependent reactions, water is oxidized to produce oxygen, and light energy is used to generate ATP and NADPH, which are energy carriers for the subsequent reactions.
What is the role of ATP and NADPH in the Calvin cycle?
-ATP provides the energy required for the reduction of carbon dioxide into sugars like glucose, and NADPH provides the electrons needed for this reduction process during the Calvin cycle.
How many ATP and NADPH molecules are required to produce one molecule of glucose in the Calvin cycle?
-To produce one molecule of glucose, the Calvin cycle requires 18 ATP molecules and 12 NADPH molecules.
Outlines
🌿 Introduction to Photosynthesis
This paragraph introduces photosynthesis, explaining the meaning of the term, which combines 'photo' (light) and 'synthesis' (building). It describes how plants use light energy to convert water and carbon dioxide into carbohydrates like glucose, while also producing oxygen as a byproduct. The reactants and products of photosynthesis are detailed, with water and carbon dioxide entering the plant and oxygen being released. The role of chloroplasts in carrying out photosynthesis is highlighted, contrasting them with mitochondria, which are responsible for cellular respiration. The paragraph also discusses the pigment chlorophyll, which is found in the thylakoids of chloroplasts, and its role in absorbing light energy. The process of photosynthesis is divided into two stages: light-dependent reactions and light-independent reactions (Calvin cycle), with the former occurring in the thylakoids and the latter in the stroma of the chloroplasts.
🔬 Light-Dependent Reactions
The second paragraph delves into the light-dependent reactions of photosynthesis, which take place in the thylakoid membranes of chloroplasts. It explains the role of photosystem II (PSII) in the electron transport chain, where light particles excite electrons in chlorophyll, leading to the oxidation of water into oxygen gas and the production of ATP and NADPH. The paragraph outlines the journey of electrons from PSII, through plastoquinone and the cytochrome b6f complex, to plastocyanin and finally to photosystem I (PSI). Here, electrons gain energy from another photon of light and are transferred to ferredoxin and then to NADP reductase, which reduces NADP+ to NADPH. The paragraph also describes chemiosmosis and the role of ATP synthase in producing ATP from ADP and phosphate, driven by the flow of hydrogen ions across the thylakoid membrane.
🌱 The Calvin Cycle
The third paragraph focuses on the Calvin cycle, the light-independent reactions of photosynthesis, which occur in the stroma of chloroplasts. It details the three stages of the cycle: carbon fixation, reduction, and regeneration of ribulose-1,5-bisphosphate (RuBP). The fixation of carbon dioxide by RuBP, catalyzed by the enzyme Rubisco, results in the formation of 3-phosphoglycerate (PGA). The subsequent phosphorylation of PGA to 1,3-bisphosphoglycerate (1,3-BPG) using ATP is catalyzed by PGA kinase. The reduction of 1,3-BPG to glyceraldehyde 3-phosphate (G3P) by NADPH is facilitated by the enzyme G3P dehydrogenase. The paragraph explains that one G3P molecule is used to produce sugars, while five G3P molecules are used to regenerate RuBP, maintaining the cycle. The summary emphasizes the role of ATP and NADPH in the Calvin cycle and the net conversion of three CO2 molecules into one G3P molecule.
🌳 Summary of Photosynthesis
The final paragraph summarizes the key points of photosynthesis, highlighting the light-dependent and light-independent reactions. It reiterates the role of PSII in converting water into oxygen and the production of ATP and NADPH during the light-dependent reactions. The Calvin cycle is reviewed, emphasizing the conversion of three CO2 molecules into one G3P molecule, requiring nine ATP and six NADPH molecules. To produce one glucose molecule, six CO2 molecules are needed, which results in the formation of two G3P molecules. This process requires double the amount of ATP and NADPH, totaling 18 ATP and 12 NADPH molecules. The paragraph concludes by reinforcing the understanding of the two processes that make up photosynthesis: the light-dependent reactions in the thylakoid membrane and the light-independent reactions (Calvin cycle) in the chloroplast stroma.
Mindmap
Keywords
💡Photosynthesis
💡Chloroplasts
💡Stomata
💡Chlorophyll
💡Light-dependent reactions
💡Calvin cycle
💡ATP
💡NADPH
💡Rubisco
💡Electron transport chain
Highlights
Photosynthesis uses light energy to build carbohydrates like glucose.
The net equation for photosynthesis combines water and carbon dioxide to produce glucose and oxygen.
Water enters the plant through the roots, while carbon dioxide enters through stomata in the leaves.
Oxygen is released through the same stomata openings in the leaves.
Chloroplasts are the organelles that carry out photosynthesis, while mitochondria are responsible for cellular respiration.
Photosynthesis and cellular respiration are exact opposites, converting each other's products and reactants.
Chlorophyll, found in thylakoids, is the pigment that absorbs light energy for photosynthesis.
Chlorophyll absorbs blue and red light but reflects green light, which is why plants appear green.
Photosynthesis is divided into light-dependent reactions in the thylakoids and light-independent reactions in the stroma.
Light-dependent reactions produce oxygen, ATP, and NADPH, while consuming water, NADP+, ADP, and phosphate.
The Calvin cycle, or light-independent reactions, reduces carbon dioxide into sugars like glucose.
The Calvin cycle involves carbon fixation, reduction, and the regeneration of ribulose biphosphate (RuBP).
Carbon dioxide reacts with RuBP to form 3-phosphoglycerate (PGA) in the carbon fixation step.
PGA is phosphorylated by ATP to form 1,3-bisphosphoglycerate (1,3-BPG), requiring kinase enzymes.
NADPH reduces 1,3-BPG into glyceraldehyde 3-phosphate (G3P), which is used for sugar production and RuBP regeneration.
The net result of the Calvin cycle is the conversion of three CO2 molecules into one G3P molecule.
To produce one glucose molecule, six CO2 molecules are needed, resulting in two G3P molecules.
The light-dependent reactions and Calvin cycle together make up the two processes of photosynthesis.
Transcripts
in this video we're going to talk about
photosynthesis just a brief introduction
into it
now what is photosynthesis
let's think about the word photo and
synthesis photo means light
synthesis means to build something
and that's what we're doing we're using
the energy provided by light to build
something in this case carbohydrates
here we have the net equation for
photosynthesis we're combining six water
molecules with six carbon dioxide
molecules
and using light
to build
simple sugars like glucose c6h1206
and we're also going to get oxygen gas
as a product as well
now on the left side of this equation
are the reactants
and on the right side are the products
the picture on the left tells you
where these molecules
enter and leave the plant
water
enters the plant
through the roots
so the plant pulls up water and minerals
that it need
through the roots from the soil
carbon dioxide
enters the leaves of the plant through
tiny openings known as stomata
and oxygen
it leaves the plant
through those same
openings
so it's important to understand that
water and carbon dioxide they go into
the plant and the plant releases oxygen
during photosynthesis
now let's move on to the chloroplasts
the chloroplast is the organelle that
carries out photosynthesis
on the other hand the organelle that is
responsible for cellular respiration is
the mitochondria
now these two processes
they are exact opposites of each other
photosynthesis
converts carbon dioxide and water with
the help of light energy into glucose
and oxygen gas
on the other hand
cellular respiration takes glucose and
oxygen gas
and converts it back into carbon dioxide
and water releasing energy in the
process
so you need to be familiar with these
two
processes
now the pigment that is responsible for
absorbing light energy
is known as chlorophyll
and chlorophyll is found in the
thylakoids
which you can see in this picture
one stack of thylakoids is known as the
granum
if you have multiple stacks
this is called
grana
so that's the plural form of the word
granum
the lumen is the fluid inside of the
thylakoid and the stroma
is the fluid inside of the chloroplast
the chloroplast has two membranes the
inner membrane and the outer membrane
and between that you have the
intermembrane space
so make sure you understand that the
chloroplast is the organelle in which
photosynthesis is carried out
now you also need to know that
chlorophyll absorbs blue light
and it absorbs the red light however
it reflects green light this is why most
plants appear green
photosynthesis can be broken down into
two stages
the light dependent reactions
and the light independent reactions
the light dependent reactions
occur inside of the thylakoids within
the chloroplast
the light independent reactions
which is basically the calvin cycle also
known as the dark reactions
they occur
in the stroma
of the chloroplasts
now the reason why they're called light
independent or dark reactions is because
they can proceed without the assistance
of light energy
the light dependent reactions
oxidizes water
into oxygen gas
and remember oxidation involves the loss
of electrons
so whenever an oxidation reaction occurs
there has to be a reduction reaction
nad plus i said that wrong nadp plus
rather
picks up those electrons and is reduced
into nadph
now some of the energy that is
transferred by light
is used
to
make atp
from adp and phosphate
atp is produced by chemiosmosis using an
enzyme called atp synthase
so for the light dependent reactions you
need to know that the products
are
oxygen gas atp
and nadph
the reactants are water
nadp plus
adp and phosphate
now let's move on to the light
independent reactions or the calvin
cycle
the calvin cycle takes in carbon dioxide
and reduces it
into
sugars such as glucose
now because that's a reductive process
oxidation has to happen somewhere
nadph
is oxidized
back into
nadp plus
so nadph it gives up its electrons
turning into nadp plus
carbon dioxide ultimately receives those
electrons and eventually turn it into
glucose
atp
is used to power that process
as atp converts back into adp and p
it energizes the calvin cycle giving it
the energy it needs to convert co2 into
glucose
so the reactants
of the calvin cycle are
carbon dioxide
atp and nadph
the products
are
sugars such as glucose
nadp plus
adp and p
so let's begin our discussion now with
the light
dependent reactions
so what we have here is the electron
transport chain inside of the thylakoid
membrane
now the first thing that's going to
happen
is a light particle will strike
photosystem 2
and it's going to excite the electrons
in chlorophyll so chlorophyll is going
to lose its electrons
which will flow into this mobile
electron carrier called
plastoquinone
now because chlorophyll lost electrons
it needs to replenish those lost
electrons
and so it's going to take the electrons
from water
oxidizing it
into oxygen gas
so one water molecule
produces one oxygen atom
and it's going to give off two hydrogen
ions
and also two electrons
so water will ultimately lose two
electrons to photosystem two
photosystem two is also called 680
because
that's the wavelength of light that has
the highest absorption it's 680
nanometers
now plastoquinone is going to carry the
electrons
to cytochrome b6f complex
and as the electrons pass through that
complex
what's going to happen next is
it's going to pump protons
from the stroma that is from outside of
the thylakoid
into the lumen or the inner thylakoid
space
so the proton concentration in the
stroma
is going to decrease
while the proton concentration
inside the thylakoid is going to
increase
producing a concentration gradient
now the electrons will continue the
journey from cytochrome b6f
to
this particular peripheral protein
plastocyanin
this is a copper containing protein
and it's going to transfer the electrons
to photosystem one
now
from this journey the electrons have
lost some of its energy
and so what's going to happen here is
the electrons
will gain more energy
by being struck by another photon of
light in photosystem one
also known as p700 so this particular
photosystem has its maximum absorption
at a wavelength of 700 nanometers
so after the electron
is struck by a photon of light
that photon will impart its energy to
the electron the electron will get
excited
and having more energy it's going to go
to
another peripheral protein called
ferrodoxin which is an iron sulfur
protein
and that's going to carry the electrons
to nadp reductase
now
napd reductase
it's a peripheral protein but it's also
an enzyme
you can see the word ace
this enzyme is going to reduce nadp plus
so the electrons
are going to leave
and they're going to
meet up with nadp plus
once nadp plus
accepts the electrons
along with a hydrogen ion
it's going to be reduced into nadph
so this reaction also reduces
the hydrogen ion concentration inch in
the stroma
which
will favor the production of atp soon
so because there's a buildup of hydrogen
ions on the inner thylakoid space
and there's
very little hydrogen ions in the stroma
what's going to happen here now is these
hydrogen ions
due to this concentration gradient
they will begin to flow through an
enzyme called atp synthase in the
process known as chemiosmosis
as those hydrogen excuse me as those
hydrogen ions flow through that enzyme
this protein will rotate in such a way
that it's going to combine adp and
phosphate to make
atp
so that's how the electron transport
chain works
in photosynthesis
so as we can see here water is oxidized
into oxygen gas
nadp reductase
produces
the electron carrier nadph
and atp synthase is used to produce atp
so those are the major products of the
light dependent reaction and keep in
mind that photosystem 2 not photosystem
1 but photosystem two is what
converts water into oxygen gas you might
be tested on that
now let's talk about the other part of
photosynthesis that is the calvin cycle
or the light independent reactions
the calvin cycle can be broken down into
three parts
the first part is the fixation of carbon
dioxide
the second part is reduction and the
third part is the regeneration of rubp
ribulose 1 5 biphosphate
so the first thing that happens is that
carbon dioxide enters the cycle
carbon dioxide is going to react with
ribulose biphosphate
catalyzed by the enzyme rubisco
and that's going to turn into
3-phosphoglycerate represented by the
symbol pga
so that's carbon fixation
rubp
is a molecule with five carbon atoms
on carbon 1
we have a phosphate group and on carbon
5 we have another phosphate group so
that's rubp
now there's three of them and they're
going to react with three co2 molecules
now when one molecule of co2 reacts with
one molecule of rubp
we're going to get initially
a6
carbon molecule but that's going to be
broken up into two
three carbon molecules
so pga is a three carbon molecule
and it's going to have one phosphate
group
so if we keep track of a total number of
carbons
if each rubp has five carbons three of
them has 15 carbons
and then we're going to add three
carbons from the three co2 molecules
so we should have a total of 18 carbons
so thus there's six
three phosphoglycerate molecules
now
the enzyme kinase when you see that that
enzyme is used to transfer a phosphate
group
to a molecule
and so this next step requires atp
we're going to use six atp molecules
to phosphorylate three phosphoglycerate
and so now we have one three by
phosphoglycerate
so we still have a three carbon molecule
but now we have a phosphate group on
carbon one
and carbon three
so as we could see here pga kinase is an
enzyme that catalyzes the conversion
of
3-phosphoglycerate into 1-3 by
phosphoglycerate
so atp
gives up a phosphate in order to become
adp
and that phosphate is transferred to
this molecule as you can see we now have
two phosphate groups so anytime you see
a kinase enzyme it catalyzes the
transfer of a phosphate group from one
molecule to another
now in the next step
we are going to use
nadph
i put it p first
we're going to use this molecule to
reduce 1 3 by phosphoglycerate into g3p
glyceraldehyde 3-phosphate
so nadph is going to convert into nadp
plus
now we need six
molecules of nadph to do this
this reaction will be catalyzed by the
g3p dehydrogenase enzyme
this enzyme
as it suggests the words dehydrogenase
it removes hydrogen from nadph
now at this point we're going to get six
g3p molecules
one
of the six g3p molecules is going to be
used to produce sugars like glucose and
fructose and things like that
the other five g3p molecules
is used to regenerate the three
ribulose biphosphate molecules
so keep in mind the total number of
carbons here is 15.
each g3p molecule
has three carbon atoms
and it has a phosphate group on carbon
3.
so 5 times 3 gives us a total of 15
carbons which is what
we started with
so notice the net result
the calvin cycle converts three
molecules of co2
into one molecule of g3p
and that is the net result of the carbon
cycle
now let's summarize what we've just
considered
in the calvin cycle we saw that three
molecules of co2 was converted into one
molecule of g3p
and that required
the use of nine atp molecules
and
six
nadph molecules
now in order to make one molecule of
glucose
we're going to need six molecules of co2
and once that enters into the carbon
cycle that's going to produce two
molecules of g3p
which can be used to produce one
molecule of glucose
and so we need to double the numbers
that's going to require
18 molecules of atp
and 12 molecules
of nadph
we just got to double everything
and so that's a simplified review of
photosynthesis
and the two process
the two processes rather that make it up
that is the light dependent reactions
which occur
inside of the thylakoid membrane and the
light independent reactions or the
calvin cycle which occurs in the stroma
of the chloropaths so keep that in mind
and that's it for this video thanks
again for watching and don't forget to
subscribe
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