PHOTOSYNTHESIS

Carbon dioxide

C6H12O6

Photosynthesis

H2OCO2 O2

Water

+ 66

Lightenergy

Oxygen gasGlucose

+ 6

6 CO2 + 12 H2OC6H12O6 + 6 O2 + 6 H2O

Reduction

Oxidation

Light energy

autotrophs (producers)

Primary consumer (prey)

Secondary consumer (predator)

Tertiary consumer

Decomposers

There is a pathway of energy flow between environment and organisms.

• During photosynthesis , green plants convert sunlight energy into chemical bond energy so it provides its own food

6CO2 +12H2O Glucose + 6O2 +6 H2O ( C6H12O6)

Solar Energy

Chlorophyll

Sunlight Energy Chemical Energy Photosynthesis

From air from soil

• Plants can also produce ATP ( energy ) by breaking down food by respiration. Autotrophs

• Animals life depend on plants for food. They get their energy from these foods and again by respiration (Heterotrophs). So sunlight is very important for energy conversion on Earth.

• Insectivourous Plants : They have chloroplast and can make photosynthesis-autotrophs

• But they live in Nitrogen poor soil so they get Nitrogen from insects that they capture.- heterotrophs

EXCEPTIONAL PLANTS

• They make extracelllar digestion.

LEAF STRUCTURE AND THE CHLOROPLAST

• Photosynthesis occurs mainly in leaf cells which carry chloroplast. Leaf cells contain:

• Epidermis : nonphotosynthetic cell layer• Mesophyll: photosynthetic parenchyma

cells (palisade and spongy parenchyme)• Stoma: embedded in the epidermis for gas

exchange• Vascular tissue that carries water and

minerals(xylem), organic molecules (phloem)

CO2 O2Stoma

Spongy parenchyma

Vascular bundle

Chloroplast

Mesophyll

Leaf structure

Leaf Epidermis

Palisade ParenchymaSpongy parenchyma

Epidermis

Chloroplast

Outer and inner membrane

Intermembrane spaceGranumStroma

Thylakoid

• Green Plant and cyanobacteria Photosynthesis :

• The source of Hydrogen in glucose is H2O

• O2 is product coming from H2O

• Chlorophyll found in chloroplast in eukaryotic organisms

6CO2 + 12 H2O Glucose +6 O2 ( CH2O)6

Solar Energy

Chlorophyll

•Bacteria Photosynthesis :•Bacteria produce only food , they don’t produce Oxygen .Because their Hydrogen supply is H2S instead of H2O

•Chlorophyll is in Cytoplasm (Prokaryotic)

Using sunlight ,CO2 and Chlorophyll and synthesis of organic matter are same

CO2 +2H2S (CH2O)6 + H2O + 2S Solar Energy

Chlorophyll

6CO2+12H2O18 C6H12O6+6H2O+6O2

18

CO2+2H2S (CH2O)n+2S+ H2O(bacteria)

CO2+2H2 (CH2O)n+ H2O (bacteria)

LIGHT ENERGY AND CHLOROPHYLL• Light is a form of photons. When a

photon meets a molecule, one of three things happens:

• The photon may be reflected by the molecule

• The photon may pass through the molecule.

• The photon may be absorbed by the molecule.

When the photon absorbed by a molecule it disappears. Its energy, however, cannot disappear, because energy is neither created nor destroyed.

• When a molecule absorbs a photon, the molecule acquires the energy of the photon. It is thereby raised from a ground state (lower energy) to an excited state (higher energy)

• When the white light (light containing visible light of all wavelengths) falls on a pigment, certain wavelengths of the light are absorbed.

Shorter

High energy

Longer

Low energy

• Molecules that absorb wavelengths in the visible spectrum are called pigments.

•

• Engelman tried to find out the the wavelengths that work best for photosynthesis. He reflected a beam of light on a green algae and added aerobic bacteria to the medium , to see the distribution of bacteria.

Is wavelength of the light important for photosynthesis?

•He found that the algae released more oxygen under the red and blue light.

Shorter

High energyLonger

Low energy

PHOTOSYNTHESIS REACTIONS

• The reactions of photosynthesis can be divided into two pathways:

1.Light reactions( depend on light energy)

Aim: to produce ATP and NADPH22.Calvin–Benson cycle,(doesn’t use

light directly Aim: to fix CO2 by using ATP and

NADPH2

Photosynthesis

LIGHT DEPENDENT

At thylakoids

LIGHT INDEPENDENT

At stroma

Aim: produce ATP, NADPH,

( O2)

Aim: Use ATP NADPH to bind

CO2 and produce organic

molecules.

NADP ve NADPH(coenzyme)Similar to NAD in mitochondria, NADP is found to accept electrons •NADP+ + 2H = NADPH + H+ •NADP accepts H and is reduced.

What are the molecules that are needed for photosynthesis?

a)Produced by themselves

b)Obtain from outside

• Chlorophyll• Chloroplast(only in eukaryotes)• Enzymes 

• H2O

• CO2

• Minerals• Light and Temperature

NADPH

Photosystem II

e–

Millmakes

ATP Ph

oto

n

Photosystem I

ATP

e–

e–

e–

e–

e–

e–

Ph

oto

n

LIGHT DEPENDENT REACTIONS

• Light reactions ; • Occurs in grana(thylakoid membrane)

of chloroplast• Depends on light energy to produce

ATP• Converts light energy into chemical

energy• Chloropyll and ETS function• Has two parts as cyclic and non-cyclic

photophosphorylation

PHOTOSYSTEMS-Reaction centers

• Photosystems are composed of pigments and proteins. Excitation energy from photons moves from pigments that absorb shorter wavelengths (higher energy) to pigments that absorb longer wavelengths (lower energy).

• There are two photosystems ( PSI, PSII ) in thylakoid membrane. Each of them has chl-a at their center but chl-a bind with different proteins so they can absorb different wavelenghts.

• ( PSI works at 700 nm,• PSII work at 680 nm) higher

energy

• When light is absorbed by chlorophyll, the chlorophyll becomes Chl+

( oxidized ) The energized electron that leaves the activated chlorophyll in the reaction center needs somewhere to go. It passes through a chain of electron carriers in the thylakoid membrane ( ETS ).There are two different systems of electron transport in photosynthesis:

• Cyclic electron transport produces only ATP.

• Noncyclic electron transport produces NADPH + H+ and ATP.

A) Cyclic photophosphorylation

• Aim: to produce only ATP• Cyclic electron transport occurs

when the ratio of NADPH + H+ to NADP+ in the chloroplast is high.

• It is called cyclic because electron passes from an excited chlorophyll molecule to the ETS and cycles back to the same chlorophyll molecule at the end of the chain of reactions.

Cyclic PhotophosphorylationPS I (700nm, chl-a)

light

Ferredoxine

Cytochrome

e-

Chl

Chl+

e-

e-

Primary e- acceptor

Plastocyanine

H are pumped to thylokoid space using the energy from high to low ETS

ATP ADP

B. Noncyclic photophosphorylation

• Aim: to produce ATP and NADPH also oxygen

• In noncyclic electron transport, light energy is used to

• oxidize water(photolysis), forming Oxygen, H+, and electrons

• Noncyclic electron transport requires two different photosystems.

_ Photosystem I (700 nm), uses light energy to reduce NADP+ to NADPH + H+.

_ Photosystem II (680 nm), uses light energy to oxidize water molecules, producing electrons, protons (H+), and O2.PS II ETS II PS I ETS I NADP+

2 NADP 2NADPH2

2H2O 4e-+4H+

+O2

4e-

Chlorophyll-a (PSI) light

Ferredoxine4e-

light

4e-

PQPC4e- 4e-

4 e-

Chlorophyll-a

Atmosphere

(PS-2)

2ATP 2ADP + 2Pi

CYT

700 nm

680nm

Primary e acceptor

4 e-

e

primaryelectronacceptor

pigment molecules

lightenergy

e

electron transportchain

ATP

e

e

Photosystem I

NADP

NADPH

e

electron transportchain e

H+

2

1/2

e

H+

+

high

low

reactioncenter

H2O

O2

Photosystem II

en

erg

y level of

ele

ctr

on

s 3

4

1

2

7 8

9

5

6

plastoquinon

cytochrome

plastocyanine

ferredoxin

H+ are pumped into the thylakoid space

ATPsynthase

photosystem I

photosystem II

thylakoidmembrane

lightenergy

+

P

ATP

NADP+

ADP

NADPH

Calvincycle

CO2

C6H12O6

sugar

e–

e–

e–

e–

e–

e–

1/2

2

H2O

electron transport chain IIelectrontransportchain I

(stroma)

(thylakoid space)

O2

A high H+ concentration iscreated in the thylakoid space

The flow of H+ down their concentration gradientpowers ATP synthesis

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

1

23

Steps of the noncyclic photophosphorylation

• Electrons from Photosystem II move through ETS to Photosystem I.

• Electrons from Photosystem I move to ferredoxin then to last e acceptor NADP.

• Photosystem II replaces its electons from water by photolysis.

• During these reactions H+ (from water -photolysis) are pumped into thylakoid space.

• Chemiosmosis in Chloroplasts• As H in the thylakoid space

increases, it creates a proton gradient. By using this gradient ATP is synthesized by chemiosmosis of H ions from thylakoid to stroma.

• Hydrogens that pass to the stroma reduce NADP+ molecules to make NADPH2

• During noncyclic electron transport ATP is produced by using two molecules of water. Also NADPH2 forms and oxygen is given to atmosphere.

• So water is electron supply for PSII,

hydrogen supply for NADP and oxygen supply for atmosphere.

• As a result during LIGHT DEPENDENT reactions for fixation of a CO2 molecule

• 3 ATP

• 2 NADPH2 are produced

• Oxygen is given to atmosphere.2H2O+3ADP+Pİ 2NADPH2+3ATP +O2

lıght

Chl.

•The needed NADPH2 and ATP are mostly provided by noncyclic phosphorylation but sometimes the cells can make also cyclic photophosphorylation when they needs more ATP

Cyclic Photophosphorylation

Noncyclic Photophosphorylation

Only PSI works( 700 nm )

Both PSI ( 700 nm) and PSII ( 680 nm ) works

Only ATP is produced

ATP , NADPH2 and oxygen are produced

Nothing used H2O is used and NADP+ is reduced

• Which one of the given statements does not occur in noncyclic reactions?

• A. Include two types of chlorophyll• B. Photophosphorylation occurs

• C. H2O is used

• D. NADPH2 is oxidized

• E. Oxygen is given to atmosphere

The Calvin–Benson CycleCO2 fixation

• Aim: to fix CO2 in air and use it to produce (CH2O)n. Also uses NADPH2 and ATP.

• Location: Stroma of chloroplast. • This step is not directly dependent

to light energy but dependent to light reactions because of ATP and NADPH2

NADPH

ATP

P

2 PGAL

P

Fixation:

CO2

1

Rubisco

P2 PGA

P

CALVINCycle

2

2

2

P

2

PGAL

P

3

PGALP GlucoseProduct:

4ATP1

1 ADP

NADP+

2 ADP +

Ribulose biphosphate RBP

unstable

2 DPGA

6 x calvin = 1 glucose

Pi

Ribulose monophosphate RMP

RBP

C3CO2

C C C6

PGA

NADP+

ATP

ADP

NADPH

6

6

6

6

C C C1

PGAL

C C C5

PGAL

ATP

ADP

3

3

C C C3

RuBP

C C C1

PGAL

+ C C C1

PGAL

C C C1

glucose

C C C

C C C6

PGAL

Calvincycle

Energy from ATPand NADPH is used to convert the sixmolecules of PGA tosix molecues of PGAL

Carbon fixationcombines three CO2

with three RuBP usingthe enzyme rubisco

Using the energyfrom ATP, five of the six molecules of PGALare converted to threemolecules of RuBP 4 One molecule of

PGAL leaves the cycle

Two molecules of PGAL combine toform glucose and other molecules

C C

5

3

4

2

1

The Calvin Cycle:• The Calvin cycle occurs in three steps:

1.Carbon fixation : This reaction is catalyzed by rubisco which combines three CO2 molecules and its product is 6 PGA.

2.The synthesis of PGAL: PGA are reduced to form a carbohydrate, 6 PGAL. 3ATP are used and 2 NADPH2 are oxidized.

3.The regeneration of ribulose bisphosphate (RuBP): ATP is used with five of the six PGAL molecules to regenerate the five-carbon RuBP necessary to repeat the cycle

• The remaining PGAL molecule, which is the end product of photosynthesis, exits the cycle

• In reactions that occur outside the Calvin cycle, two PGAL molecules can be combined to form one six-carbon glucose molecule.

• To fix 1 molecule of CO2 , 3 ATP and 2 NADPH2 are used.

• For 1 molecule glucose (6CO2 are used) the calvin benson cycle repeated at 6 times so 18 ATP and 12 NADPH2 are used during the reactions.

• Cycle is sensitive to differences in temperature.

• PGA and PGAL are used for the formation of amino acids, vitamins and nucleotides. Glucose increases the osmotic pressure in the plant cells and the cells take water and swells so it is converted into starch and cellulose in a short time ( Starch is not dissolved in water )

Synthesis of different organic molecules during photosythesis

* PGA can form pyruvate , aminoacids and fatty acids

Synthesis of different organic molecules during photosythesis

CelluloseStarch

Disaccharide

6C 3C2

N

Glycerol

Fatty acidsOrganic basesVitamins

Amino acidsGlucose

* PGA can form pyruvate , aminoacids and fatty acids

Light dependent reactions

Light independent

reactions

Takes place in

Grana of chloroplast

Stroma of chloroplast

It needs Light , water , NADP, ADP

Ezymes , CO2, ATP and NADPH2

It produces 3 ATP , 2NADPH2, oxygen

Glucose and the other organic molecules

• A plant cell releases 120 molecules O2 during light reactions.

• A.How many glucose is produced?

• B.How many ATP are used?

• C.How many NADP are reduced ?

• D.How many H2O molecules are broken down by photolysis ?

• If a plant cell uses 18 molecules

of CO2 during light independent reactions, how many PGAL and glucose molecules are produced?

• The net ATP yield of a plant cell is 114 ATP during the cellular respiration.So how many NADPH2

should be used during formation of these glucose molecules in photosynthesis?

• 195 molecules of water are needed to hydrolyze the starch molecule.How many CO2 should be used to make the monomers of this starch?

NADP+

NADPH

ATP

CO2

+

H2O

ADPP

Electrontransport

chainsThylakoidmembranes

LightChloroplast

O2

CALVINCYCLE

(in stroma)

Sugars

Photosystem II

Photosystem I

LIGHT REACTIONS

RuBP

3-PGA

CALVIN CYCLE

Stroma

G3P Cellularrespiration

Cellulose

Starch

Other organiccompounds

+

O2

H2O12 H+

NADP+ H+ NADPH

+ 2

H+

H+

H+ H+

H+

H+

H+

H+

H+H+

H+

H+

H+ H+

Photosystem II Photosystem IElectrontransport

chain

ATP synthase

LightLight

Stroma (low H+

concentration)

Thylakoid space(high H+ concentration)

ADP + P ATP

NADPH

ATP

RuBP

3

P

G3P

P

Input:CO2

1

Rubisco

3 P

Step Carbon fixation

3-PGA6 P

CALVINCYCLE

6

6

6

6

P

Step Reduction

2

2

G3P5 P

3

3

G3P1 P

Glucoseand othercompounds

Output:

Step Release of one

molecule of G3P

1

Step Regeneration of RuBP4

4ATP3

3 ADP

NADP+

6 ADP +