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Ps12 Manjula Agg Ps12 Manjula Agg Presentation Transcript

  • PHOTOSYNTHESIS CLASS-XII Manjula Agarwal Subject:Biology Category-sr. sec.
  • Raw materials required for
  • It is a process in which plants use Sunlight, chlorophyll, CO 2 & H 2 O to synthesize food 6CO 2 +12H 2 O C 6 H 12 O 6 +6H 2 O+6O 2 NUTRITION IN PLANTS Chlophyll Sunlight PHOTOSYNTHESIS
  • SITE OF PHOTOSYNTHESIS (Site Of Photosynthesis)
  • Chlorophyll pigments are present in a cell organelles called plastids-chloroplast PLASTIDS-CHOLOROPLAST Stroma(matrix) granum (stacks of thylakoids)
  • SECTIONAL VIEW OF CHLOROPLAST
  • MESOPHYLL-Palisade & spongy parenchyma Palisade cell
    • Four 5-membered rings, called pyrolle rings
    • Central core of magnesium.
    • A side chain , called the phytol chain, extends from one of the pyrolle rings in the chlorophyll molecule.
    • Chl a and Chl b are similar in structure except that the-CHO group in chlorophyll a is replaced with –CH 3 group in chlorophyll b.
    STRUCTURE OF CHLOROPHYLL
  • The chemical struture of chlorophyll PYRROLE RINGS CH3/CHO PHYTOL TAIL
    • Pigment is a substance that absorbs light of different wavelengths.
    • Chlorophyll absorbs light in the violet and blue wavelengths an also in the red region of the visible spectrum of light.
    • This portion of the spectrum between 400nm and 700nm is also known as photo synthetically active radiation (PAR).
    ABSORPTION SPECTRUM
  • Absorption spectrum wavelength,nm
    • CHLOROPHYLL
    • I t is a major pigment converts the light energy into electrical energy.
    • CAROTENOIDS
    • They absorb light of different wavelengths and funneled to the reaction centre (accessory pigments or antennae molecules)
    • They also protect the chlorophyll from oxidation.
    PIGMENTS (PHOTORECEPTOR MOLECULE) Chlorophyll a Cholorophyll b REACTION CENTRE Acessory pigments
  • PHOTOSYSTEM ( reaction centre + acessory pigments )
    • Photo system I(PSI)
    • It includes Chl a with maximum absorption at 700nm(P 700 )&other accessory pigments.
    • They are present in stroma thylakoids & non oppressed regions of Grana.
    • Photo system II (PSII )
    • It includes Chl a with maximum absorption at680nm(P 680 )&other accessory pigments.
    • They are present in the oppressed regions of Grana thylakoids.
    Types of photosystems
  • Reaction centre
    • There are two steps of photosynthesis
    • Light reaction
    • Dark reaction
    MECHANISM OF PHOTOSYNTHESIS (photochemical phase) (biosynthetic phase)
  •  
    • Chlorophyll absorbs light energy in the form of photons, get excited and release electron.
    • Electron passes through electron transport chain.
    • NADP reduces to NADPH + H +
    • Energy release in the form of ATP
    • ADP+Pi ATP
    LIGHT REACTI0N
  • Z scheme of light reaction
  • Formation of ATP in the presence of light is photophosphorylation. ADP+Pi ATP It occurs in two ways: 1.Non- cyclic and 2.cyclic Photophosphorylation
    • It includes two photo systems-PSI AND PSII.
    • When PSII(P680)absorbs light , excited and its electrons are transferred to an electron acceptor molecule.
    • Now PSII becomes a strong oxidizing agent and splits a molecule of water(photolysis of water).PSII restores the electrons from the water molecule
    • The primary e- acceptor (Phepophytin in plants) is reduced.
    • The reduced acceptor is strong a reducing agent now denotes the e - to an electron transport chain, consisting of plastoquinone, cytochrome complex and plastocyanin to PSI(P700).
    • P700 is excited by absorbing light and emits electron which is accepted by primary electron acceptor.
    • The primary electron acceptor is reduced. It transfers its electrons to Ferridoxin.
    • Ferridoxin in turns transfers the electrons to NADP which along with the protons is reduced to NADPH 2
    NON-CYCLIC PHOTOPHOSPHORYLATION
  • PHOTOLYSIS OF WATER +2e- Fd NADP reductase Electron Transport Chain PQ Cyt b 6 Cyt f PC ADP+Pi ATP
    • Splitting of water in presence of light H 2 O 2H + + 1 / 2 O 2 + 2e -
    • The electrons generated in this process are used to replace the electrons lost by P680
    • The protons are used for reducing NADP to NADPH.
    • Oxygen is liberated as a byproduct of photosynthesis.
    PHOTOLYSIS OF WATER
    • When chloroplast is illuminated with light greater than 680nm,only PSI is activated, as it has a maximum absorption at 700nm,and PSII absorbs at 680nm.remains inactivated.
    • In cyclic only PSI is involved. When it is activated by light, it emits electrons.
    • These electrons are accepted by the primary acceptor, then transfer to ELECTRON TRANSPORT CHAIN i.e. Ferridoxin,Plastoquinone, cytochromeb6&bf and then finally come back to PSI(P700).
    • This downhill movement of electrons from an electron acceptor to P700 results in the formation of ATP from ADP, and is termed as cyclic photophosphorylation. In cyclic photophosphorylation oxygen is not released (as there is no photolysis of water ) and NADPH2 is also not produced.
    CYCLIC PHOTOPHOSPHORYLATION
  • ADP+Pi ATP primary e-acceptor
  • CHEMIOSMOTIC HYPOTHESIS (mechanism of ATP synthesis)
    • Carbon dioxide is reduced to carbohydrates (carbon fixation).
    • Carbon fixation occurs in the stroma of chloroplast.
    • The process makes use of the ATP and NADPH produced in the light reaction .
    BIOSYNTHETIC PHASE (DARK REACTION)
    • It consists of three phases.
    • Carboxylation
    • Reduction
    • Regeneration of RuBP Carboxylation -
    • The first acceptor of CO 2 is Ribulose 1,5 biphosphate.6 molecules of CO2 reacts with molecules of 6 RUBP (Ribulose bi phosphate) to form a short lived 6C compound.
    • The reaction is catalyzed by RuBP carboxylase (Rubisco).
    • 6C compound breaks into 2 molecules of 3C-compound i.e.phosphoglyceric acid.
    • PGA is the first stable compound in this pathway.
    DARK REACTION (CALVIN-BENSION CYCLE)
    • 12 molecules of PGA is converted into 12 molecules of 1,3-di-phosphoglycerate and then reduced to phosphoglyceraldehyde (PGAL) using ATP and NADPH.
    • Two molecules of PGAL are used for the synthesis of glucose molecule than starch.
    • 10 molecules of PGAL by a series of complex reactions are converted into 5Ccompound,RUBP.
    • The formation of 6 molecules of RuBP needs 6 ATP molecules.
    • Total 18 ATP and 12NADPH is required in the synthesis of one molecule of Glucose.
    REDUCTION REGENERATION OF RuBP
  • C 6 H 12 O 6 DARK REACTION
      • Hatch and Slack Pathway:
    • This pathway of carbon fixation occurs in plants like maize, sugarcane, pearl millet and amaranth.
    • These plants have two types of photosynthetic cells i.e. mesophyll cells and bundle sheath cells (Kranz anatomy).
    • The chloroplast are dimorphic i.e. those in the mesophyll cells are granal and those in the bundle sheath cells agranal.
    THE C4 PATHWAY
  • Mesophyll cell Bundle sheath cell
  • THE C4 PATHWAY
    • Phospho-enol-pyruvate(PEP) is the CO2 acceptor , present in the mesophyll cells and the reaction is catalyzed by the enzyme PEP case .
    • The first stable product is oxalo acetic acid (OAA) which is a 4C-compound
    • OAA is converted into malic acid and transported to bundle sheath cells where it is decarboxylated into pyruvic acid .
    • The CO2 librated is used for Calvin cycle in the bundle sheath cells.
    • Pyruvic acid is transported back to mesophyll cells where it converts into PEP. During this conversion 2 ATP are used.
    MECHANISM OF C4 PATHWAY
  • FILL IN THE COLUMNS 2&3 IN THIS TABLE TO FIND OUT THE DIFFERENCES BETWEEN C3 AND C4 CYCLES.
  • Yes/no/not always Does the plant have PEP case ? PGA/OAA/RuBP/PEP Which is the first stable product? 5/4/3 Number of carbons in the primary CO2 acceptor RuBP/PEWP/PGA Which is the primary CO 2 acceptor? 1.Mesophyll,bundle sheath. 2. .Mesophyll How many cell types does the leaf have that fixCO2 Mesophyll/bundle sheath/both Cell type in which the initial carboxylation reaction occurs Mesophyll/bundle sheath/both the Calvin cycle Cell type in which takes place Choose from C4plants C3plants Characteristics
  • PHOTORESPIRATION
  • RuBisCO Enzyme RUBP+CO 2 2 X 3PGA {CALVIN CYCLE} RUBP +O 2 PGA + Phosphoglycolate {PHOTO RESPIRATION} Most Abundant Enzyme In The World
    • At high temperatures and limited CO 2 supply Rubisco enzyme binds with O 2 instead of CO 2 in C3 plants and enters in the cycle of photorespiration.
    • It involves interaction pf three organelles-chloroplast, peroxisome and mitochondria.
    • RUBP+O 2 Phosphoglycote+PGA
    • (CHLOROPLAST)
    • Phosphoglycolate passes through series of reactions and finally forms RUBP.
    • 75% of the carbon lost by the oxygenation of RUBP is recovered and 25% is lost as release of one molecule of CO 2.
    • No doubt it is a wasteful process but it has a useful role in protecting the plants from oxidative damage
    Photorespiration
  • FACTORS AFFECTING PHOTOSYNTHESIS
  • WATER CARBON DIOXIDE LIGHT Temperature Internal factors
  •  
    • LIGHT-The chlorophylls absorb mostly the blue and red regions of the spectrum. The rate of photosynthesis increases at the lower intensities of light and decreases at higher intensities.
    • Reason: I-other factors required for photosynthesis become limiting.
    • 2. destruction of chlorophyll occurs
    FACTORS AFFECTING PHOTOSYNTHESIS
    • The rate of photosynthesis increases with increase in temperature up to a maximum of 30oc. However the rate starts decreasing if the temperature rises beyond 3o 0 C.
    • REASON: Photosynthesis involves number of enzymes. The function of enzyme is maximum at optimum temperature. Low temperature inhibits the rate of photosynthesis as it lowers the activity of enymes.High temperature inhibits the rate of photosynthesis as as it denatures the enzymes
    TEMPERATURE
  • Rate Of Photosynthesis Effect Of Temprature On Rate Of Photosynthesis Temperature
    • The rate of photosynthesis increases with an increase in carbon dioxide concentration up to a certain level. Beyond that, carbon dioxide concentration has no effect on the rate of photosynthesis.
    • In C3 plants rate of photosynthesis increase up to 500 µ l.l -1 but in C4 plants up to300 µ l.l -1 due to two factors:
    • 1.high availability of substrate for the carboxylation reaction.
    • 2. reduced photorespiration due to more available CO 2 to RUBISCO.
    CARBON DIOXIDE
  • EFFECT OF CO2 ON THE RATE OF PHOTOSYNTHESIS
    • The rate of photosynthesis is slow in water deficient conditions because of two factors.
    • 1. Under water deficient conditions stomata remain closed to reduce the rate of transpiration. This reduce or stops the entry of CO 2 into the leaves.
    • 2.Reduced water potential.
    water
  • ACTIVITIES RELATED TO PHOTOSYNTHESIS
  • To make a temporary stained mount of lily and petunia leaf and count the number of stomata on upper and lower surface of epidermis PEEL OF LILY LEAF
  • PEEL OF PETUNIA LEAF
  • Water CO2 IS NECESSARY DURING PHOTOSYNTHESIS
  • Hydrilla OXYGEN IS LIBERATED DURING PHOTOSYNTHESIS