PHOTOSYNTHESIS
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PHOTOSYNTHESIS. VAN HELMONT’S EXPERIMENT (1649). 5 years only water. = 77 kg tree + 90,8 kg soil. 2,3 kg shoot + 90,9 kg soil. JOSEPH PRIESTLEY’S EXPERIMENT 1771. EXP. 2. EXP. 1. What do you think happened to the mouse in experiment 1?.

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Photosynthesis

PHOTOSYNTHESIS


Photosynthesis

VAN HELMONT’S EXPERIMENT (1649)

5 years

only water

= 77 kg tree + 90,8 kg soil

2,3 kg shoot + 90,9 kg soil


Photosynthesis

JOSEPH PRIESTLEY’S EXPERIMENT 1771

EXP. 2

EXP. 1

What do you think happened to the mouse in experiment 1?

What do you think happened to the mouse in experiment 2?

Why do you think that happened?

Why do you think that happened?


Photosynthesis

In the early 1900`s scientists believed that light reactions split carbon dioxide and release oxygen.

In 1930 van Neil studied bacterial photosynthesis.

CO2 + 2 H2S CH2O + H2O + 2S

C

Dark

reactions

+ H2O

C H2 O

CO2

O2


Photosynthesis

  • In bacterial photosynthesis:

  • Oxygen is not released

  • This proves that light does not split carbon dioxide in plant photosynthesis.

  • Light reactions split water and release oxygen.

Anabaena sp.


Photosynthesis

WHAT IS PHOTOSYNTHESIS?

Photosynthesis is theprocess which converts light energy into chemical energy.


Photosynthesis

WHICH ORGANISMS DO PHOTOSYNTHESIS?

  • Photosynthesis occurs in some bacteria (blue green algae), algae (green , golden-yellow, red, brown) and in plants.

  • In autotrophic eukaryotes, photosynthesis occurs inside chloroplast.

  • In autotrophic prokaryotes photosynthesis occurs in the cytoplasm.


S tructure of chloroplast

STRUCTURE OF CHLOROPLAST


S tructure of chloroplast1

STRUCTURE OF CHLOROPLAST

  • All chloroplasts contain the green pigment chlorophyll which is found in the thylakoid membranes and absorbs the light energy that initiates photosynthesis.

  • Chloroplasts like mitochondria contain DNA, RNA and ribosome and can duplicate themselves


Overall equation of photosynthesis

OVERALL EQUATION OF PHOTOSYNTHESIS

Light energy

6CO2

+ 12 H2 O

C 6 H 12 O 6

+ 6 H2 O + 6 O 2

Enzymes, ETS


Photosynthesis

What is the source of oxygen that is released?


Stages of photosynthesis

STAGES OF PHOTOSYNTHESIS

LIGHT ENERGY

WATER

CARBON DIOXIDE

ADP + Pi

GRANA

STROMA

Light reactions convert light energy into chemical energy

Dark reactions result in the reduction of carbon dioxide into glucose

ATP

NADP+

NADPH2

GLUCOSE

OXYGEN


Stages of photosynthesis1

STAGES OF PHOTOSYNTHESIS

There are two, linked stages of photosynthesis:

  • The light reactions in the grana produce ATP by photophosphorylation and split water, evolving oxygen and forming NADPH2 by transferring electrons from water to NADP+.

    2. The dark reactions (Calvin Cycle) occur in the stroma and use the energy of ATP and the reducing power of NADPH2 to form sugar from CO2.

    Dark reactions don’t require light directly, it usually occurs during the day, when the light reactions are providing ATP and NADPH2.


Light and photosynthetic pigments

LIGHT AND PHOTOSYNTHETIC PIGMENTS

  • Light falling on an object may,

    • pass through it (be transmitted)

    • be reflected (seen as colour)

    • be absorbed (has its energy converted into the energy of motion)

  • Only absorbed light is available for photosynthesis


Photosynthesis

LIGHT AND PHOTOSYNTHETIC PIGMENTS

  • Photosynthetic pigments are organic molecules that absorb light.

  • Main plant pigments are chlorophyll and carotenoids with several forms of each type.

  • The pigments absorb the visible light wavelengths.

    380nm750nm

    violetgreen red


Photosynthesis

PHOTOSYSTEMS

  • Chlorophyll a and one or more types of accessory pigments such as chlorophyll b and various carotenoids surround a single molecule of specialized chlorophyll a (P680 and P700), forming a “photo-system”.

  • Photo-system I (PSI) contains P700 and photo-system II (PSII) contains P680 at the reaction center.


Photosynthesis

Organization of Photosystems in Grana


Photosynthetic pigments

PHOTOSYNTHETIC PIGMENTS

  • Chlorophyll contains C, H, O, N and Mg in its structure. (Mg containing protein).

  • Its synthesis requires the presence of light, Fe, and K.

Chlorophyll b

  • absorbs red and blue light, reflects green

  • transfers the absorbed light to the chlorophyll a

  • molecular formula is C55 H70 O6 N 4 Mg

Chlorophyll a

  • absorbs red and blue light

  • is the primary photsynthetic pigment

  • is involved directly in converting of light energy into chemical energy

  • presence of chlorophyll a hides the effect of carotenes and xanthophyll in leaves

  • molecular formula is C55 H72 O5 N 4 Mg


Photosynthesis

PHOTOSYNTHETIC PIGMENTS


Accessory photosynthetic pigments

ACCESSORY PHOTOSYNTHETIC PIGMENTS

Caroten(orange)

Xantophyll (yellow)

Phycoerythrin (red)

Phycocyanin (blue)

They absorb light energy and transfer it to the chlorophyll.


Reactions of photosynthesis

REACTIONS OF PHOTOSYNTHESIS

LIGHT REACTIONS

DARK REACTIONS

Cyclic photophosphorylation

Non-Cyclic photophosphorylation


Light reactions

LIGHT REACTIONS

Cyclic photophosphorylation

  • Various pigments in PSI collect light, passing the energy on to P700

  • An electron with raised energy levels is accepted by ferredoxin and passed onto an ETS where ATP is produced as the energy level falls back to the starting point.


Photosynthesis

Electron Excitation


Light reactions1

LIGHT REACTIONS

Cyclic photophosphorylation

è

Plastoquinone (PQ)

Ferredoxine (Fd)

ADP + Pi

è

ATP

è

Cytochrome b6

ADP + Pi

Photosystem I

PSI ( Chl a)

è

ATP

è

Cytochrome f

light

è

Plastocyanine


Photosynthesis

The overall equation for cyclic electron transport

light

2ADP + 2Pi2ATP

chlorophyll


Light reactions2

LIGHT REACTIONS

Non-Cyclic photophosphorylation

1. When PSII absorbs light, an electron is removed from chlorophyll. This hole in PSll must be filled.

2. Water is split by photolysis.

3. Electrons from water molecule are passed to PSII and then onto PQ (plastoquinon).

4. As in cyclic photophosphorylation, ATP is produced via the ETS, with the electron dropping down to PSI.

5. Light energy also causes the release of an electron from PSI which is accepted by ferrodoxin.

6. Electrons pass from ferrodoxinto NADP leading to the production of NADPH2, with hydrogen coming from the separation of water into ions.

7. Electrons lost by PSI are replaced with the electrons coming from the ETS (PSII).


Light reactions3

LIGHT REACTIONS

Non-Cyclic photophosphorylation

Cytochrome f

2NADP+

Ferredoxine (Fd)

ADP + Pi

Plastocyanine

2NADPH + H2

ATP

Cytochrome b6

PSI ( Chl a(P700))

Plastoquinone (PQ)

è

source

light

2e-

2e-

H2O

PSII (Chl a (P680))

photolysis

½ O2

2H+

light

Byproduct


Photosynthesis

  • The products of the two types of light reactions are ATP, NADPH2 and oxygen.

  • The first two products enter the dark reactions of photosynthesis, where they become involved in the Calvin Cycle and the synthesis of PGAL and eventually of glucose.

  • Oxygen is diffused into the air.

LIGHT REACTIONS


Photosynthesis

Non-Cyclic photophosphorylation

2e-

2NADP+

4

3

2NADPH + H2

2

1

To dark reactions


Photosynthesis

Non-Cyclic photophosphorylation


Photosynthesis

Pathway of electron transport

PSII

PSI

2e-

2e-

2e-

To dark reactions

2e-

H2O

2NADP+

The overall equation for non-cyclic electron transport

2H2O + ADP+ Pi

+ 2NADP+

ATP + 2NADPH2 +O2

Dark reactions

By product


Comparison of cyclic and non cyclic photophosphorylation

COMPARISON OF CYCLIC AND NON-CYCLIC PHOTOPHOSPHORYLATION


Dark reactions calvin cycle

DARK REACTIONS(CALVIN CYCLE)

  • Dark reactions involve a series of chemical reactions, first described by Melvin Calvin.

  • CO2 is incorporated into more complex molecules and eventually carbohydrate.

  • Energy for the reactions is supplied by ATP with NADPH2 acting as a reducing agent, both coming from the light reactions.

  • As long as CO2, ATP and NADPH2 are present light is not required for the Calvin cycle to continue. That’s why they are called dark reactions.


Dark reactions calvin cycle1

DARK REACTIONS(CALVIN CYCLE)

  • Every turn of the cycle fixes one molecule of CO2 by producing two molecules of PGA and then two molecules of PGAL.

  • Thus six turns produce sufficient quantities of PGAL for the production of one molecule of glucose.

  • During dark reactions, for the incorporation of one carbon dioxide molecule into the process 3 ATP and 2 NADPH2 are used.

  • Therefore, for the synthesis of a hexose (glucose) 18 ATP and 12 NADPH2 are used.


Photosynthesis

DARK REACTIONS (CALVIN CYCLE)

6CO2

6 RuDP

6 (6C)UNSTABLE MOLECULE

6H2 O

6ADP + 6Pi

12 PGA(3C)

12ATP

6ATP

12ADP + 12Pi

12 NADPH2

12 DPGA

6 RuMP

12H2 O

12NADP+

With series of reactions

12 PGAL

10 PGAL

2 PGAL

2Pi

GLUCOSE(6C)


Factors affecting the rate of photosynthesis

FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS

PRINCIPLE OF LIMITING FACTOR (1905 –Blackman)

When a chemical process is affected by more than one factors, its rate is limited by the factor which is nearest its minimum value. (The rate of a biochemical process is limited by the factor which is nearest its minimum value.)


Internal genetic factors

INTERNAL (GENETIC) FACTORS

1. Anatomy of leaves

Surface area

Thickness of cuticle

Number of stomata

Volume of airspace

Thickness of epidermis and mesophyll

Number of chloroplasts in mesophyll

2. Amount of chlorophyll

3. Amount of enzymes

4. Accumulation of end products


External environmental factors

EXTERNAL (ENVIRONMENTAL) FACTORS

1.Light intensity

Relative rate of photosynthesis

Foot candles


Photosynthesis

2. Carbon dioxide concentration

Relative rate of photosynthesis

CO2 concentration(% by volume)


Photosynthesis

* Light intensity and carbon dioxide concentration

Relative rate of photosynthesis

High CO2 concentration

Moderate CO2 concentration

Low CO2 concentration

Light intensity


Photosynthesis

Relative rate of photosynthesis

3. Temperature

°C

25

30


Photosynthesis

*light intensity and temperature

Relative rate of photosynthesis

High intensity

Low intensity

Intensity


Photosynthesis

4. Light wavelength

Relative rate of photosynthesis

V BG Y O R

380 nm 750nm


Engelman n s experiment

ENGELMANN`S EXPERIMENT

Engelmann exposed Spirogyra cells to a color spectrum produced by passing light through a prism. He estimated the rate of photosynthesis indirectly by observing the movement of aerobic bacteria toward the portions of the algal filament emitting the most oxygen.

He observed that the bacteria aggregated most densely along the cells in theblue-violet and redportions of the spectrum.


Photosynthesis

5. Mineral concentration and amount of water

  • About 1% of water absorbed by roots is used in photosynthesis

  • Mgstructure of chlorophyll

  • Fesynthesis of chlorophyll, protein synthesis (Ferredoxin and cytochromes), PQ

  • Nstructure of chlorophyll, proteins, DNA, RNA, ATP, NAD, NADP

  • Ksynthesis of chlorophyll, growth

  • PDNA, RNA, ATP, NADP

  • Caformation of cell membrane, cell wall

  • Sprotein synthesis

  • CuPlastocyanin synthesis

  • Mn and Clcatalysts of photolysis


Photosynthesis

Mineral concentration/ amount of water

Relative rate of photosynthesis

Mineral concentration/ amount of water


Photosynthesis

6. Oxygen concentration

  • Oxygen is a competitive inhibitor of carbon dioxide fixation

  • RuDP carboxylase acts as oxygenase and causes breakdown of the RuDP. (Photorespiration-when the oxygen concentration is high)

  • The output of photosynthesis is decreased by 30-40% and even as much as 50%.

  • Affects C3 plants (ex: wheat, oat, Soya bean).

  • Some species of plants have evolved alternate modes of carbon dioxide fixation.

    Ex:C4 plants like corn, sugar cane and CAM plants(Crassulacean Acid Metabolism like desert plants). In C4 plants synthesis of one glucose requires the use of 30 ATP molecules(not 18 ATP), but there is no loss of RuDP due to photorespiration.


Photosynthesis

*Oxygen concentration

Relative rate of photosynthesis

21

oxygen concentration (%by volume)


Photosynthesis

C3 Photosynthesis : C3 plants

Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy).

Most plants are C3.


Photosynthesis

C4 Photosynthesis : C4 plants


Photosynthesis

C4 Photosynthesis : C4 plants

  • Adaptive Value:

    • Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration.

    • Has better Water Use Efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis.

    • C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbush pictured here, corn, and many of our summer annual plants.


Photosynthesis

C4 Photosynthesis : C4 plants


Photosynthesis

CAM Photosynthesis : CAM Plants


Photosynthesis

CAM Photosynthesis : CAM Plants

Adaptive Value:

  • Better Water Use Efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.).

  • When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis.

  • CAM plants include many succulents such as cactuses and agaves.


Photosynthesis

FATE OF PHOTOSYNTHETIC PRODUCTS

PGAL

Hormones

Vitamins

Nucleotides

Nucleic acids

Vitamins

Fructose

PGA

Glucose

RuDP

Glycerol +

Fatty acids

Lipids

Pyruvic acid

Sucrose

Maltose

Cellulose

Amino acids

Proteins

Cellular respiration

Starch

Products of photosynthesis; PGAL, PGA and glucose are used in various metabolic processes


Bacterial photosynthesis

BACTERIAL PHOTOSYNTHESIS


Photosynthesis

BACTERIAL PHOTOSYNTHESIS

light

CO2 + 2 H 2

(CH2 O )n + H 2O

bacteriochlorophyll

light

(CH2 O )n + H 2O+ 2S

CO2 + 2 H 2S

bacteriochlorophyll


Photosynthesis

BACTERIAL PHOTOSYNTHESIS

  • H2 or H2S are the source of electron.

  • They do not release oxygen as by product because they do not use water as electron source.

  • Bacteria do not contain chloroplasts.

  • The chlorophyll, known as bacterioclorophyll is present in the cytoplasm.

  • But blue green bacteria (cyanobacteria) contain chlorophyll a and use water so they release oxygen.


Chemosynthesis

CHEMOSYNTHESIS


Examples of chemosynthetic organisms

Examples of chemosynthetic organisms

  • Nitrifying bacteria (Nitrosomonas, Nitrobacter)

  • Sulfur bacteria

  • Iron bacteria

  • Hydrogen bacteria

  • Methane bacteria


Chemosynthesis1

CHEMOSYNTHESIS

  • Certain bacteria carry out a process in which food is made from carbon dioxide by using the energy of inorganic substances.

  • Like photosynthetic organisms, chemosynthetic bacteria fix carbon dioxide through the reactions of the Calvin Cycle.

  • However, the energy to make ATP and NADPH comes from the oxidation of organic substances, not light.

  • They are important for recycling of materials in ecosystem.


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

1. To see if carbon dioxide is necessary for photosynthesis

KOH

NaOH

I

II

What can you predict about the result of this experiment

*NaOH and KOH absorb CO2


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

2. To see if chlorophyll is necessary for photosynthesis

Predict the starch test results for the two areas shown on the leaf


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

3. To see if light is necessary for photosynthesis


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

4. To prove that organic substances are produced as a result of photosynthesis

1. Several disks are removed from a leaf before the sun rises.

2. Mass of the discs are measured

Will there be any difference between the two measurements?

3. Leaf is left to do photosytnhesis

4. Several new disks are removed from the same leaf before the sun set

5. Mass of the discs taken several hours later are measured


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

5. To show that oxygen is produced during photosynthesis

How can you prove that the gas which is produced is oxygen?


Photosynthesis

EXPERIMENTS ON PHOTOSYNTHESIS

6. To find out the source of oxygen that is produced during photosynthesis

Labeled CO2 (CO218)

Labeled O2 (O218)

Unlabeled CO2

Unlabeled O2

Labeled glucose (C6H12O618)

Unlabeled glucose (C6H12O6)

Unlabeled H2O

Labeled water (H2O18)


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