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PHOTOSYNTHESIS. VAN HELMONT’S EXPERIMENT (1649) 2,3 kg shoot + 90,9 kg soil = 77 kg tree + 90,8 kg soil 5 years only water.

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Presentation on theme: "PHOTOSYNTHESIS. VAN HELMONT’S EXPERIMENT (1649) 2,3 kg shoot + 90,9 kg soil = 77 kg tree + 90,8 kg soil 5 years only water."— Presentation transcript:



3 VAN HELMONT’S EXPERIMENT (1649) 2,3 kg shoot + 90,9 kg soil = 77 kg tree + 90,8 kg soil 5 years only water

4 What do you think happened tothe mouse in experiment 1? Why do you think that happened? What do you think happened tothe mouse in experiment 2? Why do you think that happened? JOSEPH PRIESTLEY’S EXPERIMENT 1771 EXP. 1 EXP. 2

5 In the early 1900`s scientists believed that light reactions split carbon dioxide and release oxygen. In 1930 van Neil studied bacterial photosynthesis. CO H 2 S CH 2 O + H 2 O + 2S C O2O2 Dark reactions + H 2 OC H 2 O CO2CO2

6 In bacterial photosynthesis:  Oxygen is not released  This proves that light does not split carbondioxide in plantphotosynthesis.  Light reactions split water and releas e oxygen. Anabaena sp.

7 Photosynthesis is the process which converts light energy into chemical energy. WHAT IS PHOTOSYNTHESIS?

8 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. WHICH ORGANISMS DO PHOTOSYNTHESIS?





13 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

14 OVERALL EQUATION OF PHOTOSYNTHESIS 6CO H 2 O Light energy Enzymes, ETS C 6 H 12 O H 2 O + 6 O 2

15 What is the source of oxygen that is released?

16 STAGES OF PHOTOSYNTHESIS LIGHT ENERGY WATER OXYGEN GRANA Light reactions convert light energy into chemical energy CARBON DIOXIDE GLUCOSE STROMA Dark reactions result in the reduction of carbon dioxide into glucose ADP + Pi ATP NADP + NADPH 2

17 STAGES OF PHOTOSYNTHESIS There are two, linked stages of photosynthesis: 1.The light reactions in the grana produce ATP by photophosphorylation and split water, evolving oxygen and forming NADPH 2 by transferring electrons from water to NADP The dark reactions (Calvin Cycle) occur in the stroma and use the energy of ATP and the reducing power of NADPH 2 to form sugar from CO 2. Dark reactions don’t require light directly, it usually occurs during the day, when the light reactions are providing ATP and NADPH 2.


19 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

20  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. 380nm 750nm violet green red LIGHT AND PHOTOSYNTHETIC PIGMENTS


22  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. PHOTOSYSTEMS

23 Organization of Photosystems in Grana

24 PHOTOSYNTHETIC PIGMENTS 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 C 55 H 72 O 5 N 4 Mg Chlorophyll b  absorbs red and blue light, reflects green  transfers the absorbed light to the chlorophyll a  molecular formula is C 55 H 70 O 6 N 4 Mg Chlorophyll contains C, H, O, N and Mg in its structure. (Mg containing protein). Its synthesis requires the presence of light, Fe, and K.


26 ACCESSORY PHOTOSYNTHETIC PIGMENTS Caroten(orange) Xantophyll (yellow) Phycoerythrin (red) Phycocyanin (blue) They absorb light energy and transfer it to the chlorophyll.

27 REACTIONS OF PHOTOSYNTHESIS LIGHT REACTIONS DARK REACTIONS Cyclic photophosphorylation Non-Cyclic photophosphorylation

28 LIGHT REACTIONS  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. Cyclic photophosphorylation

29 Electron Excitation

30 LIGHT REACTIONS Cyclic photophosphorylation Ferredoxine (Fd) Photosystem I PSI ( Chl a) Plastoquinone (PQ) Cytochrome b 6 Cytochrome f Plastocyanine è è è è è è ADP + Pi ATP light

31 The overall equation for cyclic electron transport 2ADP + 2P i 2ATP light chlorophyll


33 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 ferrodoxin to NADP leading to the production of NADPH 2, 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 REACTIONS Non-Cyclic photophosphorylation

34 LIGHT REACTIONS Non-Cyclic photophosphorylation PSII (Chl a (P680)) light Plastoquinone (PQ) Cytochrome b 6 Cytochrome f Plastocyanine Ferredoxine (Fd) PSI ( Chl a(P700)) H2OH2O light 2è 2e-2e- 2e-2e- ADP + Pi ATP 2NADP + 2NADPH + H 2 photolysis ½ O 2 2H + source è By product

35  T he products of the two types of light reactions are ATP, NADPH 2 and oxygen.  The first two products enter the dark reactions of photosynthesis, where they become involvedin the Calvin Cycle and the synthesis of PGALand eventually of glucose.  Oxygen is diffused into the air. LIGHT REACTIONS

36 Non-Cyclic photophosphorylation 2NADP + 2NADPH + H 2 2e-2e To dark reactions

37 Non-Cyclic photophosphorylation

38 The overall equation for non-cyclic electron transport Pathway of electron transport H2OH2O PSII PSI 2NADP + To dark reactions 2e - 2H 2 O + ADP+ P i + 2NADP + ATP + 2NADPH 2 + O 2 Dark reactions By product 2e -



41 DARK REACTIONS (CALVIN CYCLE)  Dark reactions involve a series of chemical reactions, first described by Melvin Calvin.  CO 2 is incorporated into more complex molecules and eventually carbohydrate.  Energy for the reactions is supplied by ATP with NADPH 2 acting as a reducing agent, both coming from the light reactions.  As long as CO 2, ATP and NADPH 2 are present light is not required for the Calvin cycle to continue. That’s why they are called dark reactions.

42  Every turn of the cycle fixes one molecule of CO 2 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 NADPH 2 are used.  Therefore, for the synthesis of a hexose (glucose) 18 ATP and 12 NADPH 2 are used. DARK REACTIONS (CALVIN CYCLE)

43 6 RuDP 6 RuMP 10 PGAL 12 PGAL 12 DPGA 12 PGA(3C) 6 (6C)UNSTABLE MOLECULE 2 PGAL GLUCOSE(6C) 6ADP + 6Pi 6ATP With series of reactions 12ATP 12ADP + 12Pi 12 NADPH 2 12NADP + 12H 2 O 6H 2 O 6CO 2 2Pi




47 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.)

48 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 INTERNAL (GENETIC) FACTORS

49 EXTERNAL (ENVIRONMENTAL) FACTORS 1.Light intensity Relative rate of photosynthesis Foot candles


51 2. Carbon dioxide concentration CO 2 concentration(% by volume) Relative rate of photosynthesis


53 * Light intensity and carbon dioxide concentration Light intensity Relative rate of photosynthesis High CO 2 concentration Moderate CO 2 concentration Low CO 2 concentration

54 3. Temperature Relative rate of photosynthesis °C 2530

55 *light intensity and temperature Relative rate of photosynthesis Intensity High intensity Low intensity

56 4. Light wavelength Relative rate of photosynthesis 380 nm 750nm V B G Y O R

57 ENGELMANN`S EXPERIMENT Engelmann exposedSpirogyra cells to a colorspectrum produced bypassing light through aprism. He estimated therate of photosynthesisindirectly by observing themovement of aerobicbacteria toward the portionsof the algal filament emittingthe most oxygen. He observed that the bacteria aggregated most densely alongthe cells in the blue-violet and red portions of the spectrum.

58 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

59 Mineral concentration/ amount of water Relative rate of photosynthesis Mineral concentration/ amount of water

60 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: C 4 plants like corn, sugar cane and CAM plants (Crassulacean Acid Metabolism like desert plants). In C 4 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.

61 *Oxygen concentration Relative rate of photosynthesis oxygen concentration (%by volume) 21


63 Adaptive Value : more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewerenzymes and no specialized anatomy). Most plants are C3. C3 Photosynthesis : C3 plants

64 C 4 Photosynthesis : C 4 plants

65 Adaptive Value :  Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO 2 is delivered directly to RUBISCO, not allowing it to graboxygen and undergo photorespiration.  Has better Water Use Efficiency because PEP Carboxylase brings in CO 2 faster and so does not need to keep stomata open as much (less water lost bytranspiration) for the same amount of CO 2 gain for photosynthesis.  C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbushpictured here, corn, and many of our summer annualplants. C 4 Photosynthesis : C 4 plants


67 C AM Photosynthesis : CAM Plants


69 Adaptive Value :  Better Water Use Efficiency than C3 plants under arid conditions due to opening stomata at night whentranspiration rates are lower (no sunlight, lowertemperatures, lower wind speeds, etc.).  When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given offin photosynthesis is used for respiration and CO2 given offin respiration is used for photosynthesis.  CAM plants include many succulents such as cactuses and agaves. C AM Photosynthesis : CAM Plants

70 FATE OF PHOTOSYNTHETIC PRODUCTS PGAL FructoseVitamins RuDP Glucose Sucrose Starch Maltose Cellulose PGA Pyruvic acid Cellular respiration Vitamins Hormones Amino acids Proteins NucleotidesNucleic acids Glycerol + Fatty acids Lipids Products of photosynthesis; PGAL, PGA and glucose are used in various metabolic processes

71 PHOTOSYNTHESISAEROBIC RESPIRATION Raw materials are CO 2 and H 2 O Raw materials organic food molecules and oxygen End products are organic food molecules and oxygen (results in the increase of biomass) End products are CO 2 and H 2 O (results in the decrease of biomass) Occurs in the cells that contain chlorophyll Certain cells of plants (assimilation parenchyma) Some of the protists (algae, euglena) Some the bacteria ( cyanobacteria) Occurs in most of the actively metabolizing cells

72 PHOTOSYNTHESISAEROBIC RESPIRATION Takes place in chloroplast of eukaryotic cells, in the cytoplasm of prokaryotic cells Takes place in the cytoplasm and mitochondria of eukaryotes, in the cytoplasm of prokaryotic cells Involves photophosphorylation Involves substrate level and oxidative level phosphorylation Location of ETS: Thylakoid membrane of chloroplast Location of ETS: cristae of mitochondria

73 PHOTOSYNTHESISAEROBIC RESPIRATION Principal electron transfer components: NADP + Principal electron transfer components: NAD +, FAD, CoQ, Co-A Source of electron for ETS: In non-cyclic photophosphorylation water (undergoes photolysis to yield electron, protons and oxygen) Immediate source: NADH 2, FADH 2 Ultimate source: glucose or other fuel molecules Terminal electron acceptor for ETS: In non-cyclic photophosphorylation: NADP + (becomes reduced to form NADPH 2 ) Oxygen (becomes reduced to form water)

74 PHOTOSYNTHESISAEROBIC RESPIRATION Process occurs in the presence of light Takes place all the time (day and night)


76 CO H 2 (CH 2 O ) n + H 2 O light bacteriochlorophyll CO H 2 S (CH 2 O ) n + H 2 O+ 2S light bacteriochlorophyll BACTERIAL PHOTOSYNTHESIS

77 H 2 or H 2 S 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. BACTERIAL PHOTOSYNTHESIS


79 Examples of chemosynthetic organisms Nitrifying bacteria (Nitrosomonas, Nitrobacter) Sulfur bacteria Iron bacteria Hydrogen bacteria Methane bacteria

80 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. CHEMOSYNTHESIS

81 EXPERIMENTS ON PHOTOSYNTHESIS 1. To see if carbon dioxide is necessary for photosynthesis NaOH KOH III *NaOH and KOH absorb CO 2 What can you predict about the result of this experiment

82 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

83 EXPERIMENTS ON PHOTOSYNTHESIS 3. To see if light is necessary for photosynthesis

84 EXPERIMENTS ON PHOTOSYNTHESIS 4. To prove that organic substances are produced as a resultof photosynthesis 1. Several disks are removed from aleaf before the sun rises.2. Mass of the discs are measured 3. Leaf is left to do photosytnhesis 5. Mass of the discstaken several hourslater are measured 4. Several new disks areremoved from the same leafbefore the sun set Will there be any differencebetween the two measurements?

85 EXPERIMENTS ON PHOTOSYNTHESIS 5. To show that oxygen is produced during photosynthesis How can you prove that the gas which is produced isoxygen?

86 EXPERIMENTS ON PHOTOSYNTHESIS 6. To find out the source of oxygen that is produced duringphotosynthesis Unlabeled H 2 O Labeled CO 2 (CO 2 18 ) Labeled glucose(C 6 H 12 O 6 18 ) Unlabeled O 2 Labeled water(H 2 O 18 ) Unlabeled CO 2 Unlabeled glucose(C 6 H 12 O 6 ) Labeled O 2 (O 2 18 )

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