Photosynthesis AP Biology
Summary
TLDRPhotosynthesis is a vital process in which plants and certain bacteria convert sunlight into energy. It occurs in chloroplasts, involving light-dependent reactions in thylakoids and the Calvin cycle in the stroma. Chlorophyll in photosystems absorbs light energy, exciting electrons that drive ATP production via chemiosmosis and NADPH generation. These molecules power the Calvin cycle, converting CO2 into sugars.
Takeaways
- 🌱 Photosynthesis is a process that captures energy from the sun to produce sugars, occurring in both prokaryotes and eukaryotic autotrophs.
- 🌿 In eukaryotic autotrophs, photosynthesis takes place in the chloroplast, a double membrane organelle with a compartmentalized structure.
- 🌳 The chloroplast is divided into thylakoids and the stroma, with thylakoids stacked into grana, enhancing surface area and efficiency of reactions.
- 💡 The light-dependent reactions of photosynthesis occur in the thylakoid membrane and compartment, involving proteins like photosystem 2 and photosystem 1.
- 💧 Water is split in the light-dependent reactions, producing protons, electrons, and oxygen gas as a byproduct.
- 🌞 Photosystem 2 absorbs light energy to excite electrons, which are then passed through an electron transport chain (ETC).
- 🔋 The proton pump uses energy from electron transport to establish a proton gradient, crucial for ATP production.
- 🔌 ATP synthase creates ATP by joining inorganic phosphate with ADP, powered by chemiosmosis, where protons flow down their concentration gradient.
- 🌀 The Calvin cycle takes place in the stroma, converting CO2 into organic carbohydrates with the help of ATP and NADPH produced in the light-dependent reactions.
- 🔄 NADPH and ATP are used in the Calvin cycle to power reactions, with NADPH providing electrons and ATP releasing energy for metabolic processes.
Q & A
What is photosynthesis and where does it occur?
-Photosynthesis is the process by which plants, algae, and certain bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose or other sugars. It occurs in both prokaryotes like cyanobacteria and eukaryotic autotrophs, specifically in the chloroplasts of eukaryotic cells.
What are the main components of a chloroplast?
-A chloroplast is a double membrane organelle with thylakoids that are stacked into structures called grana. The fluid region outside of the thylakoids is called the stroma. This compartmentalization helps to increase surface area and decrease competition between reactions.
What are the two main processes of photosynthesis?
-The two main processes are the light-dependent reactions, which occur in the thylakoid membrane and compartment, and the Calvin cycle, which takes place in the stroma.
Where do the light-dependent reactions take place and what happens there?
-The light-dependent reactions take place in the thylakoid membrane and compartment. Here, water is split, releasing protons, electrons, and oxygen. Electrons are excited by light energy absorbed by chlorophyll in photosystems II and I, and are passed through an electron transport chain.
What is the role of the electron transport chain (ETC) in photosynthesis?
-The ETC is involved in the transfer of electrons from photosystem II to photosystem I. As electrons move through the chain, energy is released, which is used by the proton pump to establish a proton gradient across the thylakoid membrane.
How does the proton gradient contribute to ATP production?
-The proton gradient, created by the active transport of protons from the stroma to the thylakoid compartment, is necessary for ATP production. An enzyme called ATP synthase uses the energy from the flow of protons down their concentration gradient, a process known as chemiosmosis, to create ATP from ADP and inorganic phosphate.
What is the purpose of re-exciting electrons in photosystem one after they have already been excited in photosystem two?
-The re-excitation of electrons in photosystem one is necessary to provide high-energy electrons to NADPH. These high-energy electrons are needed for certain reactions in the Calvin cycle.
What is the role of NADPH in the Calvin cycle?
-NADPH carries high-energy electrons to the Calvin cycle, where it acts as an electron carrier molecule. The electrons are used to facilitate reactions that convert CO2 into organic carbohydrates, which become sugars.
How does ATP power the reactions in the Calvin cycle?
-ATP powers the reactions in the Calvin cycle by being converted to ADP, releasing energy that can be used to drive metabolic processes and synthesize carbohydrates from CO2.
What is the significance of the term 'photophosphorylation'?
-Photophosphorylation refers to the process by which ATP is synthesized using the energy derived from light, specifically during the flow of protons through ATP synthase, which is powered by chemiosmosis.
What happens to ADP and NADP+ after they have been used in the Calvin cycle?
-After their role in the Calvin cycle, ADP and NADP+ return to the light-dependent reactions to be re-energized and reused, continuing the cycle of photosynthesis.
Outlines
🌿 Photosynthesis: Light Dependent Reactions and Efficiency
The first paragraph delves into the process of photosynthesis, highlighting its occurrence in both prokaryotes like cyanobacteria and eukaryotic autotrophs. It emphasizes the role of chloroplasts, which are compartmentalized into thylakoids and stroma, to increase efficiency by reducing competition between reactions. The light-dependent reactions are detailed, occurring in the thylakoid membrane and involving photosystems II and I, which absorb light energy to excite electrons. These reactions also produce protons, electrons, and oxygen. The paragraph explains the electron transport chain, the establishment of a proton gradient by the proton pump, and the generation of ATP through photophosphorylation powered by chemiosmosis. The role of NADP as an electron acceptor, forming NADPH which carries electrons to the Calvin cycle, is also discussed.
🌱 The Calvin Cycle: Carbon Dioxide to Carbohydrates
The second paragraph focuses on the Calvin cycle, which takes place in the stroma of the chloroplast. It describes the series of enzyme-catalyzed reactions that convert CO2 into organic carbohydrates, facilitated by the energy from ATP and electrons from NADPH produced in the light-dependent reactions. The Calvin cycle is powered by the conversion of ATP to ADP and NADPH to NADP, releasing energy for metabolic processes. The summary concludes by reiterating the interconnection between the light-dependent reactions and the Calvin cycle, with ADP and NADP being recycled back to the light-dependent reactions to continue the cycle of photosynthesis.
Mindmap
Keywords
💡Photosynthesis
💡Prokaryotes
💡Eukaryotic autotrophs
💡Chloroplast
💡Thylakoids
💡Grana
💡Stroma
💡Light-dependent reactions
💡Calvin cycle
💡Photosystems
💡Electron transport chain (ETC)
💡ATP synthase
💡NADPH
💡Chemiosmosis
💡Phosphorylation
Highlights
Photosynthesis captures solar energy to produce sugars and occurs in both prokaryotes and eukaryotic autotrophs.
In eukaryotic autotrophs, photosynthesis takes place within the chloroplast, a double membrane organelle.
Chloroplasts are compartmentalized with thylakoids and grana to increase surface area and efficiency.
The light-dependent reactions occur in the thylakoid membrane and involve a series of proteins including photosystems.
Water is split in the light-dependent reactions, producing protons, electrons, and oxygen gas.
Photosystem 2 absorbs light energy to excite electrons to a higher energy level.
Electron transport chain (ETC) involves chemical reactions that release energy for the proton pump.
The proton pump establishes a proton gradient across the thylakoid membrane.
ATP synthase creates ATP by harnessing the energy from the proton gradient through chemiosmosis.
Photophosphorylation is the process of ATP production powered by chemiosmosis and light energy.
NADP+ is the final electron acceptor in the ETC, becoming NADPH after receiving electrons.
NADPH carries electrons to the Calvin cycle to power reactions in the stroma.
The Calvin cycle involves enzyme-catalyzed reactions that convert CO2 into organic carbohydrates.
NADPH and ATP power the Calvin cycle, providing electrons and energy for metabolic processes.
The conversion of NADPH to NADP+ facilitates electron provision for reactions.
ATP to ADP conversion releases energy that can power the Calvin cycle reactions.
ADP and NADP+ return to the light-dependent reactions to continue the photosynthetic process.
Transcripts
[Music]
photosynthesis is a process that
captures energy from the sun to produce
sugars it occurs in both prokaryotes
like cyanobacteria and eukaryotic
autotrophs
in eukaryotic autotrophs photosynthesis
takes place in the chloroplast the
chloroplast is a double membrane
organelle that is compartmentalized into
thylakoids which are stacked into
structures called grana
the fluid region outside of the
thylakoids is called the stroma
compartmentalization of the chloroplast
helps to increase surface area and to
decrease competition between competing
interactions
this increases the efficiency of the
reactions that need to take place
the two main processes that occur in
photosynthesis are the light dependent
reactions which take place in the
thylakoid and the calvin cycle which
takes place in the stroma
let's first look at the light dependent
reactions which specifically take place
in the thylakoid membrane and in the
thylakoid compartment
embedded into the thylakoid membrane is
a series of proteins including
photosystem 2 a proton pump and
photosystem 1.
there are several other membrane
proteins as well that are involved in
electron transport
water is split in the light dependent
reactions this results in h plus ions or
protons electrons and oxygen gas as a
byproduct
the electrons enter photosystem 2. the
photosystems contain chlorophyll a
pigment that is capable of absorbing
light energy from the sun
photosystem 2 absorbs light energy which
is used to boost electrons to a higher
energy level the electrons become
excited
the high energy electrons are then
passed through an electron transport
chain or etc in a series of chemical
reactions
reactions that occur as the electrons
are transferred release energy that is
utilized by the proton pump
the proton pump uses the energy from
electron transport to establish a proton
gradient
protons are actively transported from
the stroma to the thylakoid compartment
there is now an electrochemical gradient
a difference in both proton
concentration and charge across the
thylakoid membrane
the proton gradient is necessary to
produce atp energy which we will talk
about in a moment
first we'll talk about what happens to
the electrons in the etc
the electrons now with lower energy
enter photosystem one
photosystem one contains the pigment
chlorophyll which absorbs light energy
and excites the electrons once again
what's the purpose of re-exciting the
electrons if we've already pumped
protons and established a concentration
gradient
high energy electrons are going to be
picked up by a molecule called nadp
nadp is the final electron acceptor
when nadp picks up electrons it becomes
nadph nadph
carries these electrons to the calvin
cycle to power reactions
simply put
nadph is an electron carrier molecule
and high energy electrons are needed for
certain reactions to take place
now we need to address the purpose of
the proton gradient and an enzyme called
atp synthase
atp synthase is a membrane enzyme that
creates atp by joining inorganic
phosphate with adp
the flow of protons down their
concentration gradient from high to low
concentration is called chemiosmosis
atp synthase is powered by chemiosmosis
as protons flow through the enzyme the
energy is used to create atp from adp
and inorganic phosphate
adp stands for adenosine diphosphate
dye meaning two phosphate groups with
the addition of inorganic phosphate we
can make energy rich atp
adenosine triphosphate
the addition of a phosphate group is
called phosphorylation
because the original source of energy
came from the sun
this process is referred to as
photophosphorylation
so
photophosphorylation by atp synthase is
powered by chemiosmosis
but the original source of energy came
from light
both the nadph and atp produced in the
light dependent reactions go on to the
calvin cycle
the calvin cycle takes place in the
stroma
during the calvin cycle a complex series
of enzyme-catalyzed reactions converts
co2 into organic carbohydrates that
become sugars
nadph and atp power the reactions of the
calvin cycle
the conversion of nadph to nadp
provides electrons to facilitate
reactions
the conversion of atp to adp releases
energy which can power metabolic
processes
let's summarize what we've learned
the light dependent reactions occur in
the thylakoids
light energy absorbed by chlorophyll in
photosystems is used to excite electrons
the power proton pump to establish a
proton gradient
atp synthase makes atp from adp and
inorganic phosphate
photophosphorylation
is powered by chemiosmosis
excited electrons are picked up by nadp
the final electron acceptor in the etc
to become
nadph
nadph goes to the calvin cycle along
with atp
the calvin cycle occurs in the stroma
atp and nadph are used to power
reactions that convert carbon dioxide
into organic carbohydrates
adp and nadp return to the late
dependent reactions
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