Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the sun, into chemical energy that can be used to fuel the organisms' activities. Carbohydrates, such as sugars, are synthesized from carbon dioxide and water.
This presentation describes in details how photosynthesis works along with its process. It also explains in details on the light-dependent and light-independent reactions.
Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the sun, into chemical energy that can be used to fuel the organisms' activities. Carbohydrates, such as sugars, are synthesized from carbon dioxide and water.
This presentation describes in details how photosynthesis works along with its process. It also explains in details on the light-dependent and light-independent reactions.
what is photosynthesis?-history background-photosynthetic pigmment system-light harvesting complex-photo oxidation of water-photophosphorylation and mechanism of electron transport
Photosynthesis (Light and Dark reaction of photosynthesis)Shekhar Tidke
Importance of photosynthesis. Light reaction of photosynthesis, Dark reaction of photosynthesis. Hill, and Blackman reaction or C3 cycle or Calvin Cycle
Photosynthesis is a oxidation reduction process in which water is oxidized and carbon dioxide is reduced to carbohydrate level, the water and oxygen being by product.
Translocation of food in plants
1. Source and sink
2. Pathway of translocation
3. Source-sink relationship/interaction
4. Source-sink pathways follow patterns
5. Materials transported
6. The mechanism of phloem transport
7. The Pressure -Flow Model
8. Phloem loading and unloading
9. Summary
Photosynthesis is a very crucial process in nature and I have cleared a lot of basics concepts in this presentation. Any student in grade 11 or 12 (medical sc/biology/biotech) or a college student from science field will be able to clear his/her concepts through this ppt.
Plz do follow my Instagram page @biologistindia
what is photosynthesis?-history background-photosynthetic pigmment system-light harvesting complex-photo oxidation of water-photophosphorylation and mechanism of electron transport
Photosynthesis (Light and Dark reaction of photosynthesis)Shekhar Tidke
Importance of photosynthesis. Light reaction of photosynthesis, Dark reaction of photosynthesis. Hill, and Blackman reaction or C3 cycle or Calvin Cycle
Photosynthesis is a oxidation reduction process in which water is oxidized and carbon dioxide is reduced to carbohydrate level, the water and oxygen being by product.
Translocation of food in plants
1. Source and sink
2. Pathway of translocation
3. Source-sink relationship/interaction
4. Source-sink pathways follow patterns
5. Materials transported
6. The mechanism of phloem transport
7. The Pressure -Flow Model
8. Phloem loading and unloading
9. Summary
Photosynthesis is a very crucial process in nature and I have cleared a lot of basics concepts in this presentation. Any student in grade 11 or 12 (medical sc/biology/biotech) or a college student from science field will be able to clear his/her concepts through this ppt.
Plz do follow my Instagram page @biologistindia
Part I
Explain the need for transport systems in multicellular plants
Describe the distribution of xylem and phloem tissue in roots, stems and leaves
Explain the absorption process in roots
Describe transport mechanisms
Part II
List factors that affects rate transpiration
Describe xerophyte properties
List the series of events that leads to translocation
For this assignment, we were instructed to create a powerpoint presentation of at least 12 slides that adequately covered an academic subject of our choice. All sources for media is cited in the work cited at the end of the presentation.
WHAT IS PHOTOSYNTHESIS?, IMPORTANCE OF PHOTOSYNTHESIS, STRUCTURAL FEATURE OF LEAF ADVANTAGE FOR PHOTOSYNTHESIS,LEAVES AND LEAF STRUCTURE,CHLOROPHYLL, TYPES OF REACTIONS, LIGHT REACTION AND DARK REACTION, CYCLIC AND NON-CYCLIC PHOTOPHOSPORYLATION, MECAHANISM OF ATP SYNTHESIS, SCHEMATIC PRESENTATION OF LIGHT REACTION, CRASSULACEAN ACID METABOLISM (CAM), C3 AND C4 PLANTS, FACTORS AFFECTING RATE OF PHOTOSYNTHESIS, INTERNAL FACTORS AND EXTERNAL FACTORS,
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
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- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
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The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
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Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Dev Dives: Train smarter, not harder – active learning and UiPath LLMs for do...UiPathCommunity
💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
See how to accelerate model training and optimize model performance with active learning
Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
This is a hands-on session specifically designed for automation developers and AI enthusiasts seeking to enhance their knowledge in leveraging the latest intelligent document processing capabilities offered by UiPath.
Speakers:
👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
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Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
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Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
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The IoT and OT threat landscape report has been prepared by the Threat Research Team at Sectrio using data from Sectrio, cyber threat intelligence farming facilities spread across over 85 cities around the world. In addition, Sectrio also runs AI-based advanced threat and payload engagement facilities that serve as sinks to attract and engage sophisticated threat actors, and newer malware including new variants and latent threats that are at an earlier stage of development.
The latest edition of the OT/ICS and IoT security Threat Landscape Report 2024 also covers:
State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
Expansion of bot farms – how, where, and why
In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
Why are attacks on smart factories rising?
Cyber risk predictions
Axis of attacks – Europe
Systemic attacks in the Middle East
Download the full report from here:
https://sectrio.com/resources/ot-threat-landscape-reports/sectrio-releases-ot-ics-and-iot-security-threat-landscape-report-2024/
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Key Trends Shaping the Future of Infrastructure.pdfCheryl Hung
Keynote at DIGIT West Expo, Glasgow on 29 May 2024.
Cheryl Hung, ochery.com
Sr Director, Infrastructure Ecosystem, Arm.
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Sidekick Solutions uses Bonterra Impact Management (fka Social Solutions Apricot) and automation solutions to integrate data for business workflows.
We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on the notifications, alerts, and approval requests using Slack for Bonterra Impact Management. The solutions covered in this webinar can also be deployed for Microsoft Teams.
Interested in deploying notification automations for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
3. Photosynthesis
• An anabolic, endergonic, carbon dioxide
(CO2) requiring process that uses light energy
(photons) and water (H2O) to produce organic
macromolecules (glucose).
SUN
photons
6CO2 + 6H2O C6H12O6 + 6O2
glucose
4. WHAT IS PHOTOSYNTHESIS?
Photosynthesis is the process by which organisms
convert light energy into chemical energy in the form
of reducing power (as NADPH or NADH) and ATP,
and use these chemicals to drive carbon dioxide
fixation and reduction to produce sugars.
������������2 + 2������2 ������ → ������������2 ������ + ������2 ������ + ������2
It is estimated that photosynthesis annually fixes
~1011 tons of carbon, which represents the storage of
over 1018 kJ of energy.
Photosynthesis, over the eons, has produced ������2 the
in Earth’s atmosphere.
5. THE BASICS OF PHOTOSYNTHESIS
• Almost all plants are photosynthetic autotrophs, as
are some bacteria and protists
– Autotrophs generate their own organic matter through
photosynthesis
– Sunlight energy is transformed to energy stored in the
form of chemical bonds
(c) Euglena (d) Cyanobacteria
(b) Kelp
(a) Mosses, ferns, and
flowering plants
6. Light Energy Harvested by Plants &
Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6
O2
7. WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen by
the human eye as different colors.
Gamma Micro- Radio
X-rays UV Infrared
rays waves waves
Visible light
Wavelength (nm)
8. WHY ARE PLANTS GREEN?
Sunlight minus absorbed
wavelengths or colors
equals the apparent color of
an object.
Transmitted light
9. WHY ARE PLANTS GREEN?
Plant Cells
have Green
Chloroplasts
The thylakoid
membrane of the
chloroplast is
impregnated with
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).
11. BRIEF HISTORY:PRIESTLEY’S EXPERIMENT
Finding that candles burn very well in air in
which plants had grown a long time, and
having some reason to think, that there was
something attending vegetation, which
restored air that had been injured by
respiration, I thought it was possible that the
same process might also restore the air that
had been injured by the burning of candles.
Accordingly, on the 17th of August, 1771,I
put a sprig of mint into a quantity of air, in
which a wax candle had burned out, and
found that, on the 27th of the same month,
another candle burned perfectly well in it.
--Joseph Priestley--
12. BRIEF HISTORY OF INVENTIONS
Priestley later discovered oxygen, which he named “dephlogisticated
air”
Antoine Lavoisier elucidated its role in combustion and respiration.
Dutch physician Jan Ingenhousz ,in 1779 demonstrated that the
“purifying” power of plants resides in the influence of sunlight on
their green parts.
In 1782,the Swiss pastor Jean Senebier showed that CO2, which he
called “fixed air” , is taken up during photosynthesis.
Nicolas-Théodore de Saussure in 1804, found that the combined
weights of the organic matter produced by plants and the oxygen
they evolve is greater than the weight of the CO2 they consume. He
concluded that water, the only other substance he added to his
system, was also necessary for photosynthesis.
The final ingredient in the overall photosynthetic recipe was
established in 1842 by the German physiologist Robert Mayer, one
of the formulators of the first law of thermodynamics, who
concluded that plants convert light energy to chemical energy.
15. PLASTIDS
major organelles found in the cells of plants and algae.
site of manufacture and storage of important chemical
compounds used by the cell.
contain pigments used in photosynthesis, and the types of
pigments present can change or determine the cell's color.
Plastids are responsible for photosynthesis, storage of
products like starch and for the synthesis have the ability to
differentiate, or redifferentiate, between these and other
forms.
All plastids are derived from proplastids (formerly "eoplasts",
), which are present in the meristematic regions of the plant.
Proplastids and young chloroplasts commonly divide, but
more mature chloroplasts also have this capacity.
16. In plants, plastids may differentiate into several forms,
depending upon which function they need to play in the
cell. Undifferentiated plastids (proplastids) may develop
into any of the following plastids:
Chloroplasts: for photosynthesis
Chromoplasts: for pigment synthesis and storage
Gerontoplasts: control the dismantling of the photosynthetic
apparatus during senescence
Leucoplasts: for monoterpene synthesis; leucoplasts
sometimes differentiate into more specialized plastids:
Amyloplasts: for starch storage and detecting gravity
Elaioplasts: for storing fat
Proteinoplasts: for storing and modifying protein
17. The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Granum Inner
membrane
Grana Stroma Thylakoid
Stroma Thylakoid compartment
18. CHLOROPLAST
The chloroplast is made up of 3 types of
membrane:
◦ A smooth outer membrane which is freely
permeable to molecules.
◦ A smooth inner membrane which contains
many transporters: integral membrane
proteins that regulate the passage in an out of
the chloroplast of small molecules like sugars
proteins synthesized in the cytoplasm of the
cell but used within the chloroplast.
◦ A system of thylakoid membranes
19.
20. Photosynthesis occurs in two distinct
phases:
1. The light reactions, which use light
energy to generate NADPH and ATP.
2. The dark reactions, actually light-
independent reactions, which use NADPH
and ATP to drive the synthesis of
carbohydrate from C������2 and H2O.
21. Thylakoids
The thylakoid membranes enclose a lumen: a system
of vesicles (that may all be interconnected).
At various places within the chloroplast these are
stacked in arrays called grana (resembling a stack of
coins).
Four types of protein assemblies are embedded in
the thylakoid membranes:
◦ Photosystem I which includes chlorophyll and carotenoid
molecules
◦ Photosystem II which also contains chlorophyll and
carotenoid molecules
◦ Cytochromes b and f
◦ ATP synthase
These carry out the light reactions of photosynthesis
22. Stroma
The thylakoid membranes are surrounded
by a fluid stroma
The stroma contains:
◦ all the enzymes, e.g., RUBISCO, needed to
carry out the "dark" reactions of
photosynthesis
◦ A number of identical molecules of DNA,
each of which carries the complete
chloroplast genome.
24. LIGHT REACTIONS (NIEL
HYPOTHESIS)
Americanmicrobiologist Van Niel studied
photosynthesis in purple sulfur bacteria.
The chemical similarity between ������2 S and
������2 O led van to propose that the general
photosynthetic reaction is
where ������2 A is ������2 O in green plants and
cyanobacteria and ������2 S in photosynthetic
sulfur bacteria
25. photosynthesis is a two-stage process in which light
energy is harnessed to oxidize ������2 A (the light
reactions):
and the resulting reducing agent [H] subsequently
reduces C������2 (the dark reactions):
26. VALIDITY OF NEIL HYPOTHESIS
1. Hill reaction :
In 1937,Robert Hill discovered that when isolated chloroplasts that
lack CO2 are illuminated in the presence of an artificial electron
acceptor such as ferricyanide, O2 is evolved with concomitant
reduction of the acceptor [to ferrocyanide]. This demonstrates that
CO2 does not participate directly in the O2 -producing reaction.
It was discovered eventually that the natural photosynthetic
electron acceptor is NADP, whose reduction product, NADPH, is
utilized in the dark reactions to reduce CO2 to carbohydrate.
2. Radioactive O :
In 1941,when the oxygen isotope 18 O became
available,Samuel Ruben and Martin Kamen directly
demonstrated that the source of the O2 formed in
photosynthesis is H2O
27. ABSORPTION OF LIGHT: CHLOROPHYLL
The principal photoreceptor in photosynthesis is
chlorophyll. This cyclic is derived biosynthetically
from protoporphyrin IX.
Has a central metal ion Mg 2+
It has a cyclopentenone ring, Ring V, fused to pyrrole
Ring III.
Pyrrole Ring IV is partially reduced in chlorophyll a
(Chl a) and chlorophyll b (Chl b), the two major
chlorophyll varieties in eukaryotes and cyanobacteria,
whereas in bacteriochlorophyll a (BChl a) and
bacteriochlorophyll b (BChl b), the principal
chlorophylls of photosynthetic bacteria, Rings II and
IV are partially reduced.
28.
29. The propionyl side chain of Ring IV is esterified to a
tetraisoprenoid alcohol. In Chl a and b as well as in
BChl b it is phytol but in BChl a it is either phytol or
geranylgeraniol, depending on the bacterial species.
In addition, Chl b has a formyl group in place of the
methyl substituent to atom C3 of Ring II of Chl a.
Similarly, BChl a and BChl b have different
substituents to atom C4.
30. QUANTUM PHYSICS OF LIGHT ABSORPTION
Electromagnetic radiation is propagated as discrete quanta
(photons) whose energy E is given by Planck’s law:
ℎ������
������ = ℎ������ =
������
where h is Planck’s constant (6.626 x 1034 J.s),
c is the speed of light (2.998 x 108 m.s-1 in vacuum),
������ is the frequency of the radiation
and ������ is its wavelength (visible light ranges in
wavelength from 400 to 700 nm).
Thus red light with ������ = 680 nm has an energy of 176
kJ.einstein-1 (an einstein is a mole of photons)
31. Molecules have numerous electronic quantum states of
differing energies. As molecules contain more than one
nucleus, each of their electronic states has an associated
series of vibrational and rotational sub-states that are closely
spaced in energy
Absorption of light by a molecule usually occurs through the
promotion of an electron from its ground state molecular
orbital to one of higher energy
But, a given molecule can only absorb photons of certain
wavelengths because, the energy difference between the two
states must exactly match the energy of the absorbed photon
(by law of conservation of energy).
The peak molar extinction coefficients of the various
chlorophylls, > 105 M-1cm-1 ,are among the highest known for
organic molecules.
32. An electronically excited molecule can dissipate its excitation energy in
many ways:
1. Internal conversion:
a common mode of decay in which electronic energy is converted to the
kinetic energy of molecular motion, i.e., to heat.
process occurs very rapidly, being complete in <10-11 s.
Many molecules relax in this manner to their ground states but
Chlorophyll molecules usually relax only to their lowest excited states.
Therefore, the photosynthetically applicable excitation energy of a
chlorophyll molecule that has absorbed a photon in its short wavelength
band, which corresponds to its second excited state, is no different than
if it had absorbed a photon in its less energetic long wavelength band.
2. Fluorescence:
electronically excited molecule decays to its ground state by emitting a
photon.
Process is much more slower than internal conversion and requires ~10-8
s.
A fluorescently emitted photon generally has a longer wavelength (lower
energy) than that initially absorbed.
Fluorescence accounts or the dissipation of only 3 to 6% of the light
energy absorbed by living plants.
However, chlorophyll in solution, where of course the photosynthetic
uptake of this energy cannot occur, has an intense red fluorescence.
33. 3. Exciton transfer:
also known as resonance energy transfer
an excited molecule directly transfers its excitation energy to nearby unexcited
molecules with similar electronic properties
process occurs through interactions between the molecular orbitals of the
participating molecules in a manner analogous to the interactions between
mechanically coupled pendulums of similar frequencies.
An exciton (excitation) may be serially transferred between members of a group of
molecules or, if their electronic coupling is strong enough, the entire group may act
as a single excited “supermolecule.”
Exciton transfer is of particular importance in funneling light energy to
photosynthetic reaction centers
4 . Photooxidation
a light-excited donor molecule is oxidized by transferring an electron to an acceptor
molecule, which is thereby reduced.
process occurs because the transferred electron is less tightly bound to the donor in
its excited state than it is in the ground state.
In photosynthesis, excited chlorophyll (Chl*) is such a donor.
The energy of the absorbed photon is thereby chemically transferred to the
photosynthetic reaction system.
Photooxidized chlorophyll, Chl +, a cationic free radical, eventually returns to its
ground state by oxidizing some other molecule.
41. CYCLIC PHOTOPHOSPHORYLATION
In cyclic electron flow, the electron begins in a pigment
complex called photosystem I, passes from the primary
acceptor to plastoquinone, then to cytochrome b6f (a similar
complex to that found in mitochondria), and then to
plastocyanin before returning to chlorophyll.
This transport chain produces a proton-motive force,
pumping H+ ions across the membrane; this produces a
concentration gradient that can be used to power ATP
synthase during chemiosmosis.
This pathway is known as cyclic photophosphorylation, and it
produces neither O2 nor NADPH. Unlike non-cyclic
photophosphorylation, NADP+ does not accept the electrons,
but they are sent back to photosystem I. NADPH is not
produced in cyclic photophosphorylation. In bacterial
photosynthesis, a single photosystem is used, and therefore is
involved in cyclic photophosphorylation.
It is favoured in anaerobic conditions and conditions of high
irradiance and CO2 compensation point.
42. Noncyclic Photophosphorylation
Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product
Primary
electron acceptor
Primary
electron acceptor
Photons
Energy for
synthesis of
PHOTOSYSTEM I
PHOTOSYSTEM II by chemiosmosis
43. PLANTS PRODUCE O2 GAS BY SPLITTING
H2O
The O2 liberated by photosynthesis is made from the
oxygen in water (H+ and e-)
44. Noncyclic Photophosphorylation
Noncyclic photophosphorylation, is a two-stage process
involving two different chlorophyll photosystems. Being a
light reaction, Noncyclic photophosphorylation occurs on
thylakoid membranes inside chloroplasts
First, a water molecule is broken down into 2H+ + 1/2 O2 +
2e- by a process called photolysis (or light-splitting). The two
electrons from the water molecule are kept in photosystem II,
while the 2H+ and 1/2O2 are left out for further use.
Then a photon is absorbed by chlorophyll pigments on
surrounding the reaction core center of the photosystem. The
light excites the electrons of each pigment, causing a chain
reaction that eventually transfers energy to the core of
photosystem II, exciting the two electrons that are
transferred to the primary electron acceptor, pheophytin. The
deficit of electrons is replenished by taking electrons from
another molecule of water. .
45. The electrons transfer from pheophytin to plastoquinone,
then to plastocyanin, providing the energy for hydrogen ions
(H+) to be pumped into the thylakoid space. This creates a
gradient, making H+ ions flow back into the stroma of the
chloroplast, providing the energy for the regeneration of ATP.
The still-excited electrons are transferred to a photosystem I
complex, which boosts their energy level to a higher level
using a second solar photon. The highly excited electrons are
transferred to the acceptor molecule, but this time are
passed on to an enzyme called Ferredoxin- NADP
reductase|NADP+ reductase(FNR) which uses them to
catalyse the reaction : NADP+ + 2H+ + 2e- → NADPH + H+
This consumes the H+ ions produced by the splitting of water,
leading to a net production of 1/2O2, ATP, and NADPH+H+
with the consumption of solar photons and water.
The concentration of NADPH in the chloroplast may help
regulate which pathway electrons take through the light
reactions. When the chloroplast runs low on ATP for the
Calvin cycle, NADPH will accumulate and the plant may shift
from noncyclic to cyclic electron flow
46. Concept of Light Reaction
• Two types of
photosystems
cooperate in the
light reactions
ATP
mill
Water-splitting NADPH-producing
photosystem photosystem
47. HOW THE LIGHT REACTIONS GENERATE ATP AND
NADPH?
Primary NADP
electron
acceptor
Energy
Primary to make 3
electron
acceptor 2
Light
Light
Primary
electron
acceptor
Reaction-
1 center NADPH-producing
chlorophyll photosystem
Water-splitting
photosystem
2 H + 1/2
48. IN THE LIGHT REACTIONS, ELECTRON
TRANSPORT CHAINS GENERATE ATP,
NADPH, & O2
Two connected photosystems collect photons of light and
transfer the energy to chlorophyll electrons
The excited electrons are passed from the primary
electron acceptor to electron transport chains
Their energy ends up in ATP and NADPH
50. CHEMIOSMOSIS POWERS ATP SYNTHESIS
IN THE LIGHT REACTIONS
The electron transport chains are arranged with the
photosystems in the thylakoid membranes and pump H+
through that membrane
The flow of H+ back through the membrane is harnessed by
ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form
NADPH
51. The production of ATP by chemiosmosis in
photosynthesis
Thylakoid
compartment
(high H+) Light Light
Thylakoid
membrane
Antenna
molecules
Stroma ELECTRON TRANSPORT
(low H+) CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE