Photosynthesis (Light Dependent and Calvin Cycle)

8/3/2019 Photosynthesis (Light Dependent and Calvin Cycle)

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PhotosynthesisBountiful Blessings of Light and Nature


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Photosynthesis

is a chemical process thatconverts carbon dioxide into organiccompounds, especially sugars, using the

energy from sunlight and water.


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Where it all Happen

Photosynthesis takes place in the leaves ofthe plant.


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External Structure of a Leaf


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External Structure

Leaf: chlorophyll containing outgrowth of astem or branch; the site of photosynthesis.

Blade (lamina): main part of the leaf.

Vein: line dividing, but not completely, theleaf into sections.

Midrib: line dividing the leaf in two.


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External Structure

Leafstalk (petiole): part of the leaf that isattached to the stem.

Stem: part of the plant that carries theleaves.

Sheath: part of the leaf that attaches thepetiole to the stem.

Stipules: small appendage at the base ofthe petiole.


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Types of Leaves


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Types of Leaves


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Leaf Arrangement


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Internal Structure of

a Leaf


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The location and structure of chloroplastsoverview

LEAF CROSS SECTION MESOPHYLL CELLLEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outer

membrane

Innermembrane

Thylakoid

compartmentThylakoidStroma

Granum

StromaGrana


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Internal Structure of a Leaf


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Material Flow through the Internal Structure


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Photosynthesis in

the Leaf


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The location and structure of chloroplastsoverview

LEAF CROSS SECTIONMESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outer

membrane

Innermembrane

ThylakoidcompartmentThylakoid

Stroma

Granum

StromaGrana


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Inside the Chloroplast (An Overview)


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Chloroplast

Organelle where photosynthesistakesplace.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected together


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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A Thylakoid Disc


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Light Dependent Reaction

Light R ti


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NADP

2H+

ADP

ATP

PSII

PSI

XY

Light Reaction

NADPH2

Solar energy

H2O O2

Solarenergy is converted to chemical energy ia ATP &NADPH2.T hey are used in the Dark reaction

a

ADP

Light Reaction


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2H+

ADP

ATP

PSII

PSI

X Y

Light Reaction

NADPH2

H2O

O2

PHOTOLYSIS of WATER

Exitedelectrons

arereleased

fromP

SII

Picked up by low enrgy electron accepter

SoloarEnerg

yisabsorbedbyPS

II

2H+O2

ADP

LIGHT REACTION Picked up by a low energy


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NADP

2H+

ADP

ATP

PSII

PSI

X Y

LIGHT REACTION

NADPH2

H2O

O2

PHOTOLYSIS of WATER

ExitedelectronsarereleasedfromP

SII

picked up by a low

energy electronaccepter

Picked up by a low energyelectron accepter

Solarenerg

yisabsorbedby

PSII

O2

1

2

3

4

5

5

6

8

7

99

10

11

12


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Light Reaction (Electron Flow)

Occurs in the Thylakoidmembranes

During the light reaction, thereare two possible routes forelectron flow:

A.Cyclic Electron FlowB.Noncyclic Electron Flow


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Cyclic Electron Flow

Occurs in the thylakoid membrane. Uses Photosystem I only

P700 reaction center- chlorophyll a

Uses Electron Transport Chain(ETC)

Generates ATP only

ADP + ATPP


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Noncyclic Electron Flow

Occurs in the thylakoid membrane Uses Photosystem II andPhotosystem I

P680 reaction center (PSII) -chlorophyll a P700 reaction center (PS I) -

chlorophyll a Uses Electron Transport Chain(ETC)

Generates O2, ATP and NADPH


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Noncyclic Electron Flow

ADP + ATP NADP+ + H NADPH Oxygen comes from the splittingof H2O, not CO2

H2O 1/2 O2 + 2H+

P


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Chemiosmosis

Powers ATP synthesis Takes place across the thylakoidmembrane

Uses ETC and ATP synthase(enzyme)

H+ move down their concentrationgradient through channels of ATPsynthase forming ATP from ADP


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ChemiosmosisH+ H+

ATP Synthase

H+ H+ H+ H+

H+ H+ high H+

concentration

H+ADP + P ATP

PS II PS IE

TC

low H+concentration

H+Thylakoid

Space

Thylakoid

SUN (Proton Pumping)


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Calvin Cycle

Carbon Fixation (light independentreaction) C3 plants (80% of plants on

earth) Occurs in the stroma Uses ATP and NADPH from lightreaction as energy

Uses CO2 To produce glucose: it takes 6turns and uses 18 ATP and 12

NADPH.


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Ph t r spir ti n


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Photorespiration

Occurs on hot, dry, bright days Stomates close

Fixation of O2 instead of CO2

Produces 2-C molecules instead of3-C sugar molecules

Produces no sugar molecules or noATP


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Photorespiration

Because of photorespiration, plantshave special adaptations to limitthe effect of photorespiration:

1. C4 plants

2. CAM plants

C Plants


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C4 Plants Hot, moist

environments 15% of plants(grasses, corn,sugarcane)

Photosynthesisoccurs in 2 places

Light reaction -

mesophyll cells Calvin cycle - bundlesheath cells

CAM Pl


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CAM Plants

Hot, dry environments 5% of plants (cactus and iceplants)

Stomates closed during day Stomates open during the night Light reaction - occurs during

the day Calvin Cycle - occurs when CO2 ispresent


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Cam plants close

their stomata inthe hottest part

of the day toconserve water

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Photosynthesis (Light Dependent and Calvin Cycle)