Photosynthesis. Photosynthesis Photosynthesis is the way that plants make food from sunlight –You take in food which is digested and then transferred

PhotosynthesisPhotosynthesis


• Photosynthesis is the way that plants make food from sunlight– You take in food which is digested and then

transferred to cells for use by mitochondria– Plants can’t “eat” so they make food which is

then transferred to the mitochondria– Mitochondria then transform the “food energy”

into chemical energy


• Why does it matter?– Source of nearly all the energy on Earth– Process by which atmospheric gases are

maintained in the ratios we need to survive


• Who photosynthesizes?

Some bacteria


• Who photosynthesizes?

Some bacteria Some protists


Mostplants


• Heterotroph: organism that must consume food

• Autotroph: organism that makes its own food (photosynthesis)


6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Carbondioxide

Water Carbohydrate Oxygen


6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Carbondioxide

Water Carbohydrate Oxygen

Vein

Epidermis

Mesophyll

Guardcells

Vein

Stoma

Epidermis


• Vein: water delivery


• Epidermis: water-proof covering of the surface of the leaf– Prevents unwanted loss of water and gases


• Stoma: Opening in the leaves– water exits

– O2 exits

– CO2 enters


• Stoma: Opening in the leaves– water exits

– O2 exits

– CO2 enters

Transpiration


• Guard cells: surround stoma– Open and close stoma


• Mesophyll: central layer of cells– contains chloroplast-rich cells– site where most photosynthesis occurs



• 2 sets of reactions:



– LIGHT DEPENDENT REACTIONS




– LIGHT DEPENDENT REACTIONS

– LIGHT INDEPENDENT REACTIONS

(Calvin cycle)


Light Dependent ReactionsLight Dependent Reactions


• Thylakoids contain pigments


• Pigments: molecules that absorb light energy


• Pigments: molecules that absorb light energy– Electrons are energized by absorbing energy

and “jumping” energy levels


• Pigments: molecules that absorb light energy– Electrons are energized by absorbing energy

and “jumping” energy levels– A specific amount of energy is required in

order for the electron of a specific atom to jump and land in another energy level

• Ex. Long jumping versus hopscotch


• Thylakoids contain the pigment chlorophyll– Chlorophylls a and b

• Absorb light on opposite ends of the visible light spectrum

• Between 500 and 600 nm light is reflected• Why chlorophyll appears green


• Thylakoids contain the pigment chlorophyll

Absorbed AbsorbedReflected


• Thylakoids contain pigments called carotenoids– Absorb light below 550 nm– Appear red, orange, and yellow


• Thylakoids contain pigments called carotenoids

Absorbed Reflected


• Thylakoids contain pigments– Which pigment is dominant in deciduous trees

right now?


• Pigment in the thylakoids form Photosystems– Network of pigments held together within a

protein matrix– Channel energy absorbed from light to a

specific pigment molecule: reaction center chlorophyll


• Pigment in the thylakoids form Photosystems– Reaction center chlorophyll passes the

energy (via an energized electron) to a primary electron acceptor: Ferredoxin


• Process of replacing the electrons that follows this step depends on the organism:– Bacteria: cyclic – Algae and plants: non-cyclic


• Cyclic phosphorylation– Bacteria– Contain only 1 photosystem: Photosystem I– From electron acceptor, electrons go through

electron transport system from which ATP is produced

– Electrons then return to Photosystem I


• Non-cyclic phosphorylation– Algae and plants– Contain 2 photosystems: Photosystem I, and

Photosystem II– PS II acts first


• Non-cyclic phosphorylation– Photon of light energy excites electron which

is passed from PS II to electron transport chain and then to PS I

– Another photon of light re-excites the electron now in PS I which passes the electron to the primary electron acceptor and through a series of reactions


• Non-cyclic phosphorylation– Electrons lost from PS II must be replaced

• PS II takes an electron from protein Z• Protein Z then takes an electron from water by

splitting a water molecule into H+ ions and O

• H+ ions are used later, O forms O2 and is “exhaled”


• Electron transport chains– Series of enzymes embedded in membrane

called the cytochrome complex– Receive excited electrons from PS II and PS I– Electrons are passed from 1 molecule to the

next


• Electron transport chains– Energy from the electrons energized in PS II

powers a proton pump – Proton pump pumps protons into the thylakoid

space– Results in high concentration of protons in the

thylakoid space– Concentration gradient powers ATPase


• Electron transport chains– ATPase allows protons back out of membrane– Rush of protons provides enough energy to

attach a phosphate to an ADP forming

– This process is called chemiosmosis

ATP


• Electron transport chains– Energy from the electrons energized in PS I is

passed to a reduction complex – At the reduction complex NAD+ is transformed

into NADH


• Electron transport chains– NAD+ is an electron acceptor: it holds on to

the energy from the electrons until it can be used to bind a phosphate group to an ADP


• Electron transport chains– and NADH produced leave the thylakoid

to participate in the next set of reactions: the light independent reactions or Calvin cycle

ATP


Ferredoxin


Ferredoxin

Z


Ferredoxin

Energy is taken from theelectrons and is used to

make ATP from ADP

Z


Feredoxin

Ferredoxin


make ATP from ADP

Z


Ferredoxin

Ferredoxin


make ATP from ADP

Energy is takenfrom the

electrons and is used to

make NADPHfrom NADP

Z


Ferredoxin

Ferredoxin


make ATP from ADP

Energy is takenfrom the

electrons and is used to

make NADPHfrom NADP

ATP and NADPH leave the thylakoid and enter the stromawhere they are used in the Calvin cycle

Z


Light

2e-

Ferredoxin

Water molecule is splitby protein Z

H2O

O

2H+

+

2e-

Photosystem II

Electron Transport System

Energy is removed from the electrons as they move down the ETC. The energy is used to pump p+ into thylakoid. p+s power ATPase which converts ADP to ATP

ADP + Pi + Energy → ATP

2e-

2e-

FerredoxinElectron Transport

System

NADPH

+H+

2e-

NADP+

+2H+

Light

ATP and NADPHleave thylakoidand enter stromato be used in theCalvin cycle

Oxygen isreleased as a

by-productZ

Cytochromecomplex

NADPHreductas

e

Photosystem I

Light Independent ReactionsLight Independent Reactions(Calvin cycle)(Calvin cycle)

Calvin cycleCalvin cycle

• Uses ATP and NADPH produced in the light-dependent reactions

• Also uses CO2 taken in through stoma

• Requires no sunlight

• Produces carbohydrate which is used by mitochondria in respiration


(3 PGA) (From lightdependentreactions)


(3 PGA) (From lightdependentreactions)

(From lightdependentreactions)


(PGA) (From lightdependentreactions)




RuBP

CO2

Rubisco

3 PGA ATP

NADPH

ADP

NADP+

Pi

G3P

Output for use bymitochondria inrespiration

G3P(carbohydrate)

G3P

ATP

ADP

1,3 Bisphosphoglycerate

CARBON FIXATION

REDUCTION

REGENERATION OFRuBP


3 CO2 + 3 RuBP → 6 PGA


3 CO2 + 3 RuBP → 6 PGA↓Rubisco


3 CO2 + 3 RuBP → 6 PGA → → 6 G3P↓Rubisco



↓6 ATP



↓6 ATP

↓6 NADPH


3 CO2 + 3 RuBP → 6 PGA → → 6 G3P ↓Rubisco

↓6 ATP

↓6 NADPH

output

↓


3 CO2 + 3 RuBP → 6 PGA → → 6 G3P → 3 RuBP ↓Rubisco

↓6 ATP

↓6 NADPH

output

↓



↓6 ATP

↓6 NADPH

output

↓

↓ATP



↓6 ATP

↓6 NADPH

output

↓

↓ATP


3 CO2 + 3 RuBP → 6 PGA



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Photosynthesis. Photosynthesis Photosynthesis is the way that plants make food from sunlight –You take in food which is digested and then transferred