PHOTOSYNTHESIS

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

JOSEPH PRIESTLEY’S EXPERIMENT 1771 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?

In 1930 van Neil studied bacterial 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

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.

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

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.

STRUCTURE OF CHLOROPLAST

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 Light energy 6CO2 + 12 H2 O C 6 H 12 O 6 + 6 H2 O + 6 O 2 Enzymes, ETS

What is the source of oxygen that is released?

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 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 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

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. 380nm 750nm violet green red

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.

Organization of Photosystems in Grana

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 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 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

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 LIGHT REACTIONS DARK REACTIONS Cyclic photophosphorylation Non-Cyclic photophosphorylation

Cyclic photophosphorylation 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.

Electron Excitation

Cyclic photophosphorylation 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

The overall equation for cyclic electron transport light 2ADP + 2Pi 2ATP chlorophyll

Non-Cyclic photophosphorylation 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 ferrodoxin to 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).

Non-Cyclic photophosphorylation LIGHT REACTIONS Non-Cyclic photophosphorylation 2è Cytochrome f 2è 2NADP+ Ferredoxine (Fd) ADP + Pi 2è Plastocyanine 2NADPH + H2 ATP 2è 2è Cytochrome b6 2è PSI ( Chl a(P700)) Plastoquinone (PQ) è source light 2e- 2e- H2O PSII (Chl a (P680)) photolysis ½ O2 2H+ light By product

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

Non-Cyclic photophosphorylation 2e- 2NADP+ 4 3 2NADPH + H2 2 1 To dark reactions

Non-Cyclic photophosphorylation

PSII PSI To dark reactions H2O 2NADP+ 2H2O + ADP+ Pi + 2NADP+ Pathway of electron transport PSII PSI 2e- 2e- 2e- 2e- To dark reactions 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 Pathway of è CYCLIC NON-CYCLIC First è donor PSI WATER Last è acceptor NADP+ Products ATP ATP, NADPH2, O 2 Numbers of PS involved PSI ONLY PSI and PSII

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 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.

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 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 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 1.Light intensity Relative rate of photosynthesis Foot candles

2. Carbon dioxide concentration Relative rate of photosynthesis CO2 concentration(% by volume)

* Light intensity and carbon dioxide concentration Relative rate of photosynthesis High CO2 concentration Moderate CO2 concentration Low CO2 concentration Light intensity

3. Temperature Relative rate of photosynthesis °C 25 30

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

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

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 the blue-violet and red portions of the spectrum.

5. Mineral concentration and amount of water About 1% of water absorbed by roots is used in photosynthesis Mg structure of chlorophyll Fe synthesis of chlorophyll, protein synthesis (Ferredoxin and cytochromes), PQ N structure of chlorophyll, proteins, DNA, RNA, ATP, NAD, NADP K synthesis of chlorophyll, growth P DNA, RNA, ATP, NADP Ca formation of cell membrane, cell wall S protein synthesis Cu Plastocyanin synthesis Mn and Cl catalysts of photolysis

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

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.

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

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.

C4 Photosynthesis : C4 plants

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.

C4 Photosynthesis : C4 plants

CAM Photosynthesis : CAM Plants

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.

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

PHOTOSYNTHESIS AEROBIC RESPIRATION Raw materials are CO2 and H2 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 CO2 and H2 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

PHOTOSYNTHESIS AEROBIC 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

PHOTOSYNTHESIS AEROBIC 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: NADH2, FADH2 Ultimate source: glucose or other fuel molecules Terminal electron acceptor for ETS: In non-cyclic photophosphorylation: NADP+ (becomes reduced to form NADPH2) Oxygen (becomes reduced to form water)

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

BACTERIAL PHOTOSYNTHESIS

BACTERIAL PHOTOSYNTHESIS light CO2 + 2 H 2 (CH2 O )n + H 2O bacteriochlorophyll light (CH2 O )n + H 2O+ 2S CO2 + 2 H 2 S bacteriochlorophyll

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

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

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.

EXPERIMENTS ON PHOTOSYNTHESIS 1. To see if carbon dioxide is necessary for photosynthesis What can you predict about the result of this experiment NaOH KOH I II *NaOH and KOH absorb CO2

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

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

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

EXPERIMENTS ON PHOTOSYNTHESIS 6. To find out the source of oxygen that is produced during photosynthesis Labeled water (H2O18) Unlabeled CO2 Unlabeled glucose (C6H12O6) Labeled O2 (O218) Unlabeled H2O Labeled CO2 (CO218) Labeled glucose (C6H12O618) Unlabeled O2