Photosynthesis

Slide 1 : APT ACADEMIC SOLUTIONS believes in people who will deliver the right solutions, and it proudly possesses them.

Dr. Pankaj KumarDirector – Apt Academic Solutions : Dr. Pankaj KumarDirector – Apt Academic Solutions A Doctorate in Biology has a great depth eClass management. With his international exposure in imparting, Dr Pankaj enriches company’s brand value to make it a name to recon with. The Anchor

Slide 3 :

Slide 4 : Session objectives

Slide 5 : Photosynthesis 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 It is a process of oxidation and reduction Water is oxidised CO2 is reduced Raw materials required are pigments, light, water and CO2

Slide 6 : Photosynthesis Light Reaction Dark Reaction

Slide 7 : Photosynthetic pigments Carotenoids Carotenes Xanthophylls Phycobilins Phycocyanin Phycoerythrin Chlorophylls Chlorophyll a Chlorophyll b Chlorophyll c Chlorophyll d Chlorophyll e Bacteriochlorophyll

Chlorophyll : Chlorophyll Porphyrin head and phytol tail. Porphyrin head consists of four pyrrole rings Mg2+ is present at its centre Mg2+ is bounded to pyrrole ring by two covalent and two co-ordinate bond Light is essential for biosynthesis of chlorophyll Chlorophyll molecule consists of two parts Chlorophyll a has a methyl (–CH3) group while chlorophyll b has an aldehyde (–CHO) group on ring II of porphyrin head (carbon no. –3) Phytol tail is absent in chlorophyll c

Slide 9 : Chlorophyll extract is prepared in? Ethyl alcohol Acetone Petroleum ether Chloroform Illustrative Problem

Carotenoids : Carotenoids Structurally related to phytol Soluble in fats and other organic solvent Biosynthesis does not require light Occurs in chloroplast and chromoplast Carotene has general formula of C40H56 Orange – yellow in color Lycopene is a type of carotene – found in purple sulpher bactria, tomato, red chillies, roses etc Three main types of carotene are a, b & g a b g

Do You Know ? : Do You Know ? What is the fate of b carotene in animals ? b carotene is converted into vitamin A C40H56 + 2H2O = 2 C19H27CH2OH (Vitamin A) Leaf turns yellow in the absence of light. Why ? Absence of sunlight Degradation of Chlorophyll Unmasking of caotenoids Yellow color of carotenoids appear

Xanthophyll & Phycoblins : Xanthophyll & Phycoblins Yellow or brown pigment Oxygen containing derivatives of carotene Xanthophyll has general formula of C40H56O2 Most common forms are Lutein, Zeaxanthin, fucoxanthin Blue or red in color Phycoblins are of three types – phycocyanin, phycoerythrin and allohycocyanin Water soluble pigments What is Pteridines ?

Absorption & Action Spectra : Absorption & Action Spectra Absorption spectrum is the amount of light absorbed by pigment, plotted as function of wavelength Action spectrum is the actual rate of photosynthesis in terms of oxygen evolution or carbon utilization, plotted as function of wavelength There is a close correlation between the absorption and action spectra

Absorption Spectra of photosynthetic pigments : Absorption Spectra of photosynthetic pigments The absorption maxima of chlorophyll a is 430 and 662 nm For chlorophyll b maxima is 453 and 642 nm The absorption maxima of carotenoids lies in the range of 425 – 490 nm The absorption maxima of phycoblins lies in the range of 500 – 650 nm

Slide 15 : Emerson’s First Effect (Red drop) Emerson’s Second Effect of Enhancement Emerson’s Effects Emerson (1957) measured Quantum yield in Chlorella in different wavelengths of monochromatic lights The yield dropped suddenly in the region above 680 m (red region) This fall in photosynthetic yield beyond red region is called 'red drop' or Emerson's first effect.

Emerson’s Effects : Emerson’s Effects Quantum yield was enhanced beyond 680 m by combined effect of short and long wavelengths of light This enhancement is known as Emerson's second effect

Slide 17 : Emerson’s conclusions Photosynthesis involves two light reactions carried out by two different PHOTSYSTEMS chlorophyll a – chl a680 which absorbs short wavelength --- PS II other pigments and chlorophyll a – chl a700 which absorbs long wavelength ---PS I

Photosynthetic Unit : Photosynthetic Unit It consists of antenna molecule and reaction center Antenna complex harvest light energy and channel the excitation energy to the reaction center Once the energy reaches the reaction center, a special pair of chl. molecules carries out photochemistry and an excited electron is transferred to an electronacceptor molecule

Illustrative Problem : Illustrative Problem The number of photosynthetic pigments in a photosynthetic Unit is 200 250 300 350 Ans: Photosynthetic unit consists of 300 pigments out of which 240 is Chlorophyll molecule

Reaction center : Reaction center PS I or P700 PS II or P680 PS I is located in both stroma and grana lamellae It is mostly made up of Chl. ‘a’ (Chl. a >> Chl. b) Accessory pigments are comparatively less PS II is located mainly in grana lamellae It is made up of both Chl. ‘a’& ‘b’ (Chl. a > or = Chl. B) Asociated with photolysis of water and release of O2

Slide 21 : Which pigment system is inactivated in red drop? (AICBSE-PMT, 2001) PS I and PS II PS I PS II None of these Ans: PS II ( At higher wavelength of light PSII is deactivated as it is sensitive to light of smaller wavelength Illustrative Problem

Excitation of pigments : Excitation of pigments Pigments are arranged according to increasing absorption spectra Pigments shows the phenomena of fluorescence Energy is transferred from antenna molecule to reaction center by Inductive Resonance

Slide 23 : Dark Reaction or Thermochemical Phase i. Carboxylation ii. Phosphorylation iii. Reduction iv. Regeneration of RuBP Mechanism of Photosynthesis Light Reaction or Photochemical Phase i. Non-cyclic pathway ii. Cyclic pathway

Slide 24 : Noncyclic electron transport pathway PS I & PS II is involved Photolysis occurs & O2 is released e- is transferred from water to PS II e- from PSII goes to PSI and finally to NADP

Slide 25 : Pheophytin PQ Cytochrome Plastocyanin Ferredoxin red. sub. NADP+ Ferredoxin H2O NADPH+ Assimilatory products are NADPH+ & ATP

PQ Pump : PQ Pump e- e- NADPH+ e- e- H+ H+ H+ H+ H+ H+ H+ ATP Stroma

Illustrative Problem : Illustrative Problem Source of H+ ions in intra-thylakoidal space in chloroplast is Water PQ pump CO2 Both a & b Ans: d ; Photolysis of water and PQ pump

Slide 28 : Cyclic electron transport pathway

Cyclic electron transport pathway : Cyclic electron transport pathway Only PS I is involved No Photolysis hence no release of O2 Loss of e- by PS I is compensated by its own electron PQ pump operates Assimilatory product in the form of ATP

Photophosphorylation : Photophosphorylation Coupling of ADP and iP in the presence of light ATP is formed Explained by Chemo-osmotic hypothesis of Mitchell H+ H+ ATP O2 Stroma

Slide 31 : During light reaction of photosynthesis which of the following phenomenon is observed for cyclic phosphorylation as well as noncyclic phosphorylation? (Delhi-PMT, 2001) Release of O2 Formation of ATP Formation of NADPH Involvement of PS I and PS II Ans: Formation of ATP Illustrative Problem

Energetics : Energetics One quanta or photon of light is required to move one electron For the release of one molecule of O2 , 8 photons are required – 4 photons each by PSI and PSII 18 ATP & 12 NADPH+ are formed as a result of release of 6 molecules of O2 4H2O = 4OH- + 4H+ 4OH- = 4e- + 4OH 4OH = 2H2O + O2 12H2O + 18ADP + 12NADP 6H2O + 6O2+ 18ATP + 12NADPH+

HOMEWORK : HOMEWORK What is the number of ATP formed during release of 30 molecules of Oxygen in light reaction of photosynthesis ? What is the number of photons required by PS II for the formation of 4 molecules of oxygen ? In bacterial photosynthesis O2 is not released. Why ?

Slide 34 : Dark Reaction (Calvin or C3 cycle) Dark Reaction or Thermochemical Phase can be divided into following stages i. Carboxylation ii. Phosphorylation iii. Reduction iv. Regeneration of RuBP Calvin experimented on green alga __________ by ______________technique and worked out the details of C3 cycle

Carboxylation : Carboxylation RUBP – 5 carbon compound binds with CO2 to form 6-carbon unstable compound Binding occurs in the presence of RUBISCO- the most abundant protein on this earth Unstable compound splits into two molecules of 3 carbon compound 3-PGA CO2 + RUBP 6C compound (unstable) 2 x 3-PGA

Phosphorylation : Phosphorylation 3-PGA is phosphorylated in the presence of enzyme phosphoglycero kinase ATP is consumed 1,3-diPGA is formed 3-PGA + ATP 1,3-diPGA + ADP

Reduction : Reduction 1,3-diPGA is reduced into PGAL Reaction occurs in the presence of enzyme Dehydrogenase & NADPH2 PGAL + NADP 1,3-diPGA + NADPH2

Regeneration of RUBP : Regeneration of RUBP PGAL through series of reaction forms 6-C compound fructose RuBP is regenerated with the help of one molecule of ATP PGAL Fructose STARCH RuMP RuBP Enz ??

Slide 39 : Calvin cycle

Slide 40 : What is the number of ATP and NADPH2 molecules required to fix 1 CO2 molecule during Calvin cycle? (AICBSE-PMT, 2002) 3 ATP and 1 NADPH2 3 ATP and 2 NADPH2 2 ATP and 3 NADPH2 3 ATP and 3 NADPH2 Ans: 3 ATP and 2 NADPH2 Illustrative Problem

Illustrative Problem : Illustrative Problem For the fixation of one molecule of carbohydrate, calvin cycle will run? One time Two times Six times Twelve times Ans: c Single carbon is fixed in one cycle, hence six turn of cycle is needed for a molecule of carbohydrate

Slide 42 : C4 plants Sugarcane, maize Kranz leaf anatomy: Vascular bundles surrounded by a layer of bundle sheath cells Dimorphic chloroplasts: Large size in bundle sheath cells; normal size in mesophyll cells

C4 cycle (Hatch and Slack pathway) : C4 cycle (Hatch and Slack pathway) PEP OAA MALATE MALATE Pyruvate Aspartate Aspartate MESOPHYLL CELL BUNDLE SHEATH CELL

Slide 44 : C4 cycle (Hatch and Slack pathway)

C4 cycle (Hatch and Slack pathway) : C4 cycle (Hatch and Slack pathway) Mesophyll Cell PEP act as CO2 acceptor 4-C compound Oxaloacetic acid is formed OAA is converted into Malic acid Malic acid is transported into bundle sheath cell Aspartic acid in some cases is transferred to bundle sheath cell Bundle Sheath Malic acid is decarboxylated CO2 is utilized in Calvin cycle Pyruvate is transported back to mesophyll cell CO2 acceptor - PEP is regenerated

Energetics : Energetics 5 ATP and 2 NADPH2 is required for the fixation of one molecule of CO2 18 additional ATP is required in comparison to C3 plants

Difference between C3 & C4 plants : Difference between C3 & C4 plants

Slide 48 : Which of the following enzyme helps in CO2 fixation during C4 cycle? (AICBSE-PMT, 2000) RuBP carboxylase PEP carboxylase RuBP oxygenase PGA Ans: PEP carboxylase Illustrative Problem

Photorespiration : Photorespiration Light dependent respiration Chlorolast, peroxisome and Mitochondria are involved in the process RUBISCO shows oxygenase activity under higher ratio of O2 /CO2 RuBP splits into 3-C compound 3-PGA and 2-C compound phosphoglycolate Glycolate act as substrate for photresiration

Slide 50 : Chloroplast Calvin cycle RuBP Glycolate Peroxysome

Slide 51 : Peroxysome Glycolate Glyoxylate Glycine Mitochondria Mitochondria Glycine Hydroxy pyruvate Calvin cycle in Chloroplast 3-PGA

Slide 52 : Photorespiration

Photorespiration : Photorespiration Glycolate is transferred to peroxisome In the presence of O2 Glyoxylate is formed Glyoxylate is aminated to glycine Glycine is transferred to Mitocondria 2 molecules of glycine together form one molecule of 3-C compound serine and one molecule of CO2 Serine is finally transported back to chloroplast

Slide 54 : Photorepiration is negligible in C4 plants. Why ? Kranz anatomy ensures perfect carboxylase activity of Rubisco in bundle sheath cell. Red light is the most efficient light for photosynthesis. Why ? In red light loss of energy is minimum, hence it is most efficient in comparison to other light

CAM (Crassulacean acid metabolism) : CAM (Crassulacean acid metabolism) In CAM plants stomata open in night and closes in day CO2 accumulation is similar to that of C4 plants CO2 fixation and assimilation is not separated spatially but in time CAM helps plant to thrive in conditions of High daytime temperatures Intense sunlight Low soil moisture. Some examples of CAM plants are Cacti, Bryophyllum,pineapple etc

Slide 56 : At Night CAM plants take in CO2 through their open stomata The CO2 joins with PEP to form the 4-carbon oxaloacetic acid. This is converted to 4-carbon malic acid that accumulates during the night in the central vacuole of the cells. In the morning, Stomata close The accumulated malic acid leaves the vacuole and is broken down to release CO2 The CO2 is taken up into the Calvin (C3) cycle

Slide 57 : PEP OAA MALATE MALATE Pyruvate NIGHT DAY MALATE VACUOLE Stomata close

Factors affecting Photosynthesis : Factors affecting Photosynthesis External Internal

CO2 : CO2 CO2 is needed during the dark reactions where it is fixed into organic compounds The normal atmospheric concentration of CO2 is 0.03-0.04% With the increase in concentration the photosynthetic rate increases  The short-term optimum is about 0.5% but this can cause damages over long periods, What is compensation point ?

Slide 60 :

Light : Light Light intensity  As light intensity increases, the rate of photosynthesis increases linearly - until  other factors become limiting and the rate of photosynthesis levels off Effect of high light intensity is known as Solarization which occurs due to photo-oxidation of chlorophyll

Temperature : Temperature As temperature increases up to a specific optimum, the rate of photosynthesis increases. This is due to the fact that photosynthesis is an enzyme-controlled process and enzymes, being proteins, are temperature sensitive

Oxygen : Oxygen Rate of photosynthesis increases with the increase in the concentration of oxygen Beyond 21% concentration, decrease in the rate of photosynthesis is observed What is Warburg effect ?

Limiting Factor : Limiting Factor Proposed by Blackman If a process is simultaneously under control of several factors, the factor which is minimum in number controls the metabolic process and is known as limiting factor

Slide 65 : Translocation of solutes Carbohydrates are translocated from leaves to roots and storage organs along the phloem in the form of sucrose at the rate of 100 cm/hr Expenditure of metabolic energy

Slide 66 : Evidences for translocation of organic solutes: Ringing or girdling experiment Translocation of solutes

Slide 67 : In which form food is translocated in plants? (AICBSE-PMT, 2002) Starch Sucrose Glucose Galactose Ans: Sucrose Illustrative Problem

TEST : TEST 15 Questions Each question carries 3 marks -1 mark for incorrect response Question will be displayed once for 30 seconds

Class Exercise - 1 : Class Exercise - 1 Source of oxygen in photosynthesis is ? (a) water (b) carbon-dioxide (c) carbohydrate (d) both a & b

Class Exercise - 2 : Class Exercise - 2 Assimilatory product formed during non-cyclic photophosphorylation is (a) ATP & FAD (b) ATP only (c) ATP & NADH (d) none

Class Exercise - 3 : Class Exercise - 3 Photolysis occurs in Thylakoidal membrane Inter-thylakoidal space (c) Intra-thylakoidal space (d) none

Class Exercise - 4 : Class Exercise - 4 In the absence of CO2, assimilatory product formed during non-cyclic photophosphorylation is ATP only (b) NADP only (c) Both ATP & NADP (d) none

Class Exercise - 5 : Class Exercise - 5 Which of the following chlorophyll is of least molecular weight Chlorophyll a (b) Chlorophyll b (c) Chlorophyll c (d) Chlorophyll d

Class Exercise - 6 : Class Exercise - 6 Pressure potential in completely plasmolysed cell is a. positive  b. negative c. zero d. can’t say

Class Exercise - 7 : Class Exercise - 7 Which of the following element plays prominent role during photolysis a. Cl b. Mn c. Ca d. All of the above

Class Exercise - 8 : Class Exercise - 8 Pitcher of a Nepanthes is a modified Leaf tip (b) Petiole (c) Leaf blade (d) Mid rib

Class Exercise - 9 : Class Exercise - 9 Energy transfer among pigments during photosynthesis occurs through (a) fluorescence (b) phosphoresce (c) Inductive resonance (d) Both a & c

Class Exercise - 10 : Class Exercise - 10 No. of photons required for the release of one molecule of O2 is (a) 2 (b) 4 (c) 8 (d) 16

Class Exercise - 11 : Class Exercise - 11 Cu containing photosynthetic intermediate of light reaction is PQ Cyt. b (c) Plastocyanin (d) Ferrodoxin

Class Exercise - 12 : Class Exercise - 12 Correct sequence during cyclic phosphorylation is PS II ----PQ-----cyt-----PSI PS I ----PQ-----cyt-----PSI PS I ---- fd ----- cyt-----PSI (d) PS II ----PQ-----cyt-----PSII

Class Exercise - 13 : Class Exercise - 13 ATP synthesis during photosynthesis occurs at Intra thylakoidal space (b) Inter thylakoidal space (c) Thalkoidal membrane (d) stroma

Class Exercise - 14 : Class Exercise - 14 Which of the following is a bacterial disease Red rot of sugarcane (b) Whiptail disease of Cauliflower (c) Brown spot disease of Rice (d) Little leaf disease of Brinjal

Class Exercise - 15 : Class Exercise - 15 Root pressure is Active force (b) Passive force (c) Both a & b (d) Either a or b

ANSWER : ANSWER

Slide 85 :