A. Structures of PSblogs.4j.lane.edu/sanderson/files/2018/10/01_PhotosynthesisNotes_IB-Bio-C.pdf1. carboxylation of RuBP to make Glyceraldehyde-3-Phosphate 2. Glyceraldehyde-3-Phosphate

Vein

Leaf cross section

Mesophyll

CO2 O2Stomata

A. Structures of PS• Site of PS in plants:

• mostly in leaves• in chloroplasts

Inside the chloroplast

• Identify the structures in the diagram

Chloroplast

Mesophyll

5 µm

Outer membrane

Inner membrane

Thylakoid intermembrane

space

ThylakoidGranumStroma

1 µm

• Chloroplasts

• thylakoids

• grana

• stroma

6H2O + 6CO2 ------> C6H12O6+ 6O26 waters

6 carbon dioxides(plus light E, makes...)

1 glucose6 oxygen

B. The Net Reaction of Photosynthesis

Net Reaction• photolysis (hydrolysis) of water

• e- of H --> sugar• O --> O2

6 CO2 12 H2OReactants:

Products: C6H12O6 6 H2O 6 O2

Figure 10.4Photosynthesis is a redox process

Water is oxidized, carbon dioxide is reduced

• we will stay (mostly) conceptual

• follow the energy

II. PS Overview

• Occur in the inter membrane space of thylakoids1. absorption of photons generates excited e-

2. split water3. release oxygen4. produce ATP

a. ETC uses e- from PSII to make proton gradientb. ATP synthase in thylakoid membranes makes ATP

5. e- from PSI reduce NADP• E transfer

A. Light Dependent Rxns

• aka The Calvin cycle• in the stroma1. carboxylation of RuBP to make

Glyceraldehyde-3-Phosphate2. Glyceraldehyde-3-Phosphate —> G3P

• Req ATP for energy• Req NADPH for reducing power

3. G3P (aka triose phosphate)• triose phosphate used to regenerate RuBP &

make carbs• Req ATP to regenerate RuBP

B. Light Independent Rxns

PS Overview

PS Overview

PS Overview

III. Closer look at LD Rxns

• How does the chloroplast absorb light?

• Pigments

• chlorophyll a,b

• accessory pigments

Photosynthetic Pigments: The Light Receptors

Excited state

Ene

rgy

of e

lect

ion

Heat

Photon (fluorescence)

Chlorophyll molecule

Ground statePhoton

e–

Figure 10.11 A

• When a pigment absorbs light

• ground state --> excited state (unstable)

Excitation of Chlorophyll by Light

Photosystems• Light harvesting

complexes• aka “antenna

pigment mols”• pigment mols

bound by proteins

• funnel energy to reaction center

• e- gets bumped• p680 (PSII)• p700 (PSI)

Primary election acceptor

Photon

Thylakoid

Light-harvesting complexes

Reaction center

Photosystem

STROMA

Thyl

akoi

d m

embr

ane

Transfer of energy

Special chlorophyll a

molecules

Pigment molecules

THYLAKOID SPACE (INTERIOR OF THYLAKOID)Figure 10.12

e–

Mill makes ATP

ATP

e–

e–e–

e–

e–

Phot

on

Photosystem II Photosystem I

e–

e–

NADPH

Phot

on

Figure 10.14

Analogy for the Lt Rxns

Noncyclic electron flow• Produces NADPH, ATP, and oxygen

© 2014 Pearson Education, Inc.

The biomass (dry weight) of a tree comes primarily from

A. soil. B. water. C. air. D. organic fertilizer (manure, detritus). E. light.

© 2014 Pearson Education, Inc.

The light reactions, which involve the very hydrophobic chlorophyll, are located here in the chloroplast.

A.

B.C. (lumen)

E.

D.

© 2014 Pearson Education, Inc.

What colors of light will drive photosynthesis by green plants most efficiently?

A. red only B. yellow only C. green only D. blue only E. red and blue

© 2014 Pearson Education, Inc.

How are the light reactions and the Calvin cycle connected?

A. The light reactions provide ATP to the Calvin cycle, and the Calvin cycle provides NADPH for the light reactions.

B. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns ADP and NADP+ to the light reactions.

C. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns reduced sugars to the light reactions.

D. The light reactions provide NADPH to the Calvin cycle, and the Calvin cycle provides RuBP to the light reactions.

E. The light reactions provide RuBP to the Calvin cycle, and the Calvin cycle returns G3P to the light reactions.

• Occurs:

• Sim to Citric Acid Cycle (aka Krebs) in CR

• opposite of anaerobic glycolysis

• 3 phases

• C-fixation

• Reduction

• Regeneration of the CO2 acceptor

Calvin Cycle

The Calvin Cycle

The Calvin Cycle• Starts w/ CO2 + enzyme Rubisco +RuBP

• 3 “turns” of Calvin make...

• 3-C sugar

• 6 “turns” = 1 glucose

The Calvin Cycle• Three phases...

• Fixation

• CO2 + RuBP + Rubisco

• Reduction

• requires ATP (for E)

• requires H (from NADPH)

• produces 3-C sugars: G3P

• 1/6 of which form Glu

• Regeneration

• 5/6 of 3-C sugars regenerate RuBP

• requires ATP

• aka Cyclic Phosphoryllation

• Under certain conditions

• ATP deficit

• excess NADPH, deficit of NADP+

• bumped e-’s take an alternative path

• generates ATP

Cyclic Electron Flow

• Only photosystem I is used• Only ATP is produced (no O2 or NADPH)

Primary acceptor

Pq

Fd

Cytochrome complex

Pc

Primary acceptor

Fd

NADP+

reductaseNADPH

ATPFigure 10.15 Photosystem II Photosystem I

NADP+

Cyclic Electron Flow

Effect of Light Intensity

• low light => not enough ATP, NADPH

• what would be rate limiting step in Calvin Cycle?

• unusual unless the plant is heavily shaded

Effect of CO2 Concentration

• low CO2 => what would be rate-limiting step?

• this is a common limiting factor

Effect of Temperature

• low temps => rate of rxn = ____

• high temps => CO2 fixation doesn’t work