photosynthesis hour 2

7/30/2019 Photosynthesis Hour 2

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Powerpoint@lecture Slides Are Prepared By Biology Lecturer, KMPk
mailto:point@lecturemailto:point@lecture


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PREVIOUSLESSON


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SUBTOPICS

16.3 Light Dependent Reaction


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OBJECTIVE

Explain the photoactivation of chlorophyll

resulting in the conversion of light energyinto ATP and reduced NADP+


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Stages of Photosynthesis

1. Light Dependent

Reactions

- thylakoid

membranes

2. Light IndependentReactions

- stroma


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- transform light

energy into

chemical energy

that is trapped and

carried by ATP and

NADPH to Calvin

cycle


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Excitation of Chlorophyll by Light

When a chlorophyll molecule absorbs a photon

of light,

An electron boosts to an orbital of higherenergy

Pigment molecule in an excited state.


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Photosystem

Chlorophyll molecules are organized along with

other small organic molecules and proteins into

complexes called photosystem.Light harvesting complex of thylakoid

membrane.


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Photosystem:

Composed of :

Reaction center complex

organized association of protein holding special pair

of chlorophyll a molecules

Light harvesting complex: antenna molecule

Primary electron acceptor

traps excited state electrons released from thereaction center chlorophyll.

The reaction center complex contain molecule

capable for accepting electron and become reduced.


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Types of photosystems

Photosystem I

reaction center: P700

Absorption peak: 700 nm

Photosystem II

reaction center: P680

Absorption peak: 680 nm


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Photosystem Harvest Light

Photon strikes a pigmentmolecule in light harvesting

complex (antenna molecule)

Energy passed from onemolecule to another

Until reaches reaction center

complex

An excited electron fromreaction center chrolophyll

transferred to primary electron

acceptor


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a

(Accessory pigment)

1

2

3


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Light Dependent Reaction

Photophosphorylation

Process of generating ATP from ADP and phosphate

by chemiosmosis, using a proton motive force

generated across the thylakoid membrane ofchloroplast during light reaction of photosynthesis

Types:

Non cyclic photophosphorylation

Cyclic photophosphorylation


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Photophosphorylation


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Non-cyclic Photophophorylation


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non-cyclic photophosphorylation

1.pigments in

photosystem II absorbs light

electron

excited

captured by the

primary electron acceptor

chlorophyll molecules in

the reaction centre loses an

electron & become oxidized


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2.Enzyme catalyzewater splitting.

Electrons from

hydrogen atom are

transferred to P680.


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The important of water photolysis

To replace electron in photosystem II

H2O 2H+ +2e- + O2

The proton (H+) are used to reduced NADP+.

Oxygen is given off or used in respiration

Water photolysis


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3. The electrons from primary electron

acceptor of PSII are pass along an

electron transport chain, before

ending up at an oxidizedphotosystem I reaction center.

a series of

carriers thatpass

electron from

one to another

electron transport

chain


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4. The energy lost when these electrons

pass along the electron transport chain

and will used to form ATP from ADP

-chemiosmosis

5 At th b tt f thi l t t t h i th


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5. At the bottom of this electron transport chain, theelectrons fill an electron hole in an oxidized P700 center.

electron

Hole is created when photons excite

electrons on the Photosystem I

At th


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At the same

time,P700 absorbs

photon and

electron areemitted and

accepted by

primary electron

acceptorof PS I

6 Th l d h l h i


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6. Then electron are passed to the electron transport chain,

ferrodoxin (Fd) and then to an enzyme called NADP+

reductase This chain doesnt create a proton

gradient, not produce ATP


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NADP+ reductase catalyse the transfer

of electron frm Fd to NADP+

2 e- + NADP+ + 2H+ NADPH


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Photosystem I acts as its own,

without photosystem II

The P700 molecule which is

the reaction centre of

photosystem I absorbs photon

and become energised the

electron


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The electron are

emitted and taken

up by the primary

electron acceptor



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The electrons pass along the

electron transport chain,

before back to reaction

centre of PSI

The energy lost when these

electrons pass along the

transport chain and will usedto form ATP from ADP

-chemiosmosis


C li d li


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Cyclic and noncyclic

photophosphorylation occur at the

same time.

C i i f li d


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Comparision of cyclic and

non-cyclic photophosphorylation

Non-cyclicPhotophosphorylation

CyclicPhotophosphorylation

Involve PS I and PS II Involve only PS I

e- flow is non-cyclic e- flow is cyclic

H2O is 1st e- donor From PS I (P700)

Last e- acceptor is NADP PS 1 (P700)

Products are ATP,NADPH and O2

ATP is produce


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QUESTIONS

1. What is photolysis?

2. What is photophosphorylation?

3. What are the products of non-cyclic

photophosphorylation?

4. How are photosystem I and photosystem II

similar? How are they different?


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16.4 Light independent reaction/

Calvin Cycle

photosynthesis hour 2

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