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Photosynthesis powerpoint
 

Photosynthesis powerpoint

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    Photosynthesis powerpoint Photosynthesis powerpoint Presentation Transcript

    • Topic 7 Photosynthesis
    • Photosynthesis: Capturing Energy
    • Autotrophs and Chemotrophs
      • Carbon fixation is the process of building complex carbon compounds from simple carbon compounds.
          • Autotrophs organisms that fix carbon, using carbon dioxide as a carbon source, and combine it with water
          • Photoautotrophs provide nearly all the energy used by living systems on Earth
    • Overview of Photosynthesis
      • Photosynthesis is a redox reaction:
      • Carbon dioxide is reduced to sugar
      • Water is oxidized to molecular oxygen
    • Light energy converted into chemical energy
      • Producers contain chlorophyll
      • Chlorophyll can trap light energy (photons).
      • The chlorophyll convert this energy into chemical energy.
      • The chemical energy is transferred as bond energy (electrons)and is transferred in turn to other chemical energy stores called carbohydrates, lipids and protein.
      • These molecules are called organic molecules.
    • Photosynthic Active Wavelengths
      • Photosynthesis uses only small visible portion of the electromagnetic spectrum
      • Wavelengths of visible light most important for photosynthesis.
      • The symbol for wavelength is 
    • The Sun
      • The sun is a star
      • It has very high surface temperatures
      • It produces a vast amount of electromagnetic radiation of widely varying frequencies
        • Gamma-rays, which have very short wavelengths
        • To the far-infrared (much longer )
    • Leaf Structure
      • Leaves have a layered organization
      • The mesophyll tissue (middle layers of cells) is the main site of photosynthesis
      • Sap flows through the veins
    • Upper epidermis.
      • Transparent cells
      • Covered in a waxy cuticle which decreases water loss
    • Palisade layer
      • cylindrical cells
      • filled with chloroplasts (usually several dozen of them)
      • Site of photosynthesis
      • (arrows point to stomata)
    • Spongy Mesophyll layer
      • irregular in shape and loosely packed.
      • their main function seems to be the temporary storage of sugars and amino acids synthesized in the palisade layer.
    • Stomata
      • microscopic pores found on the under side of leaves.
      • bounded by two half moon shaped guard cells that function to vary the width of the pore.
    • The Chloroplast • Double outer membrane • Internal membranes called thylakoids which is the location of the light dependent reaction • Stroma surrounding the thylakoids and inside the double membrane. This is the location of the light independent reaction that includes the Calvin cycle. • The stroma often contains starch grains and oil droplets both products of photosynthesis
    • Pigments
      • A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed).
    • Chlorophyll
      • Chlorophyll is a complex molecule. Several modifications of chlorophyll occur among plants and other photosynthetic organisms.
    • Chlorophyll a
      • All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll a.
      • Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths.
      • Chlorophyll a is the main photosynthetic pigment in all organisms except bacteria
    • Accessory pigments
      • Accessory pigments absorb energy that chlorophyll a does not absorb. Accessory pigments include chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids (such as beta-carotene).
    • Compare wavelength absorbed
      • 1. Chlorophyll a: Light to medium green. Main photosynthetic pigment.
      • 2. Chlorophyll b: Blue-green. Accessory Pigment.
      • 3. Carotene: Orange. Accessory Pigment.
      • 4. Xanthophyll: Yellow. Accessory Pigment.
    • Light absorption by chlorophyll
      • Absorption spectra are obtain
      • from samples of pigment.
      • Different wavelengths of
      • light are passed through
      • and the absorption is
      • measured using a colorimeter.
      • This absorption spectra for
      • chlorophyll shows:
      • • absorption of blue light
      • • absorption of red light
      • • green light is reflected.
    • Action Spectrum:
      • Notice the Y-axis is rate of
      • photosynthesis
      • • The rate of photosynthesis is
      • measured at different
      • wavelengths.
      • • The maximum rate are at the
      • blue end and red end of the
      • visible spectrum.
      • • The lowest rates are in the
      • yellow greens.
      • • Chlorophylls are absorbing blue
      • and red light well but not green.
    • Photolysis: Energy is absorbed to produce ATP , H + and O 2
      • Photolysis is the process in which:
      • • light is absorbed by the chlorophyll
      • molecules on the thylakoid
      • membranes of the chloroplast.
      • • Light energy is converted to
      • chemical energy in the form of
      • electrons
      • • The electron bring about chemical
      • changes that include the formation
      • of ATP , H + and O 2
    • Partition of Function in the Chloroplast
      • The light-dependent reactions (the harvesting of light) occur on the thylakoid membrane.
      • The carbon fixation reactions
      • (formation of carbohydrate) occur in the stroma.
    • Photosynthesis occurs in two main phases :
      • 1. Light Dependent Reaction in which
      • A. Energy of sun is trapped by chlorophyll molecules (oxidation)
      • B. ADP is reduced to ATP with NADP + reduced to NADPH.
      • C. The reaction must have light to take place.
      • D. This reaction takes place on the thylakoid membranes. 
      • 2. The Light Independent Reaction which
      • A. Uses the chemical energy from the LDR to fix atmospheric carbon into organic molecules such as glucose.
      • B.The process does not require light and can occur in both the light and dark periods.
      • C.This reaction takes place in the stroma
    • Photosystem I and II
    • Light Dependent Reaction (LDR)
      • • Light passes through the leaf until until it reaches the chloroplast
      • • Light is absorbed by chlorophyll a in Photosystem II (a number of different chlorophyll's working together).
      • • The chlorophyll absorbs the light energy and converts this to chemical energy in the form of electrons.
      • • Photosystem II is oxidized, releasing electrons
      Stages of Light Dependent reaction:
      • • The electrons from PS II pass along membrane proteins (in thylakoid)
      • • The membrane proteins like cytochrome are reduced
      • • The reduced membrane protein pumps H + from the stroma into the space inside the thylakoids.
    • Protons Build up Inside Thylakoids
      • • At the same time as a) Photosystem I (having a different chlorophyll combination) absorbs light with a peak absorption of 680nm.
      • • The chlorophyll molecule releases electrons in the oxidation of PS I
      • • PS I is now oxidized.
      • • The electrons pass from PSI to other membrane proteins named here as ferrodoxins
      • • These proteins bring about the reduction of NADP + to NADPH + H +
      • • NADPH is found in the stroma and is used in the light independent reaction
      • To continue absorbing light PSI must be reduced back to its 'ground state’
      • • The source of electrons for this reduction are those passed to cytochrome from PSII
      • • PS II must also be reduced and returned to its 'ground state' to maintain light absorption
      • • The source of electrons is water.
      • • Electrons are removed for PS II which leaves a source of H + and
      • Oxygen
      • • Oxygen is a waste product of photosynthesis
    • Summary diagram of Oxidative Photophosphorylation
    • Summary diagram of Oxidative Photophosphorylation
      • Note:
            • The arrangement of the membrane proteins and photosystem's
            • • The electron transfer along proteins
            • • sequence of coupled oxidations and reduction
            • • build up of protons (Hydrogen ions) in the thylakoid lumen
            • • Formation of NADPH, ATP and Oxygen
    • Cyclic Photophosphorylation: This is a biochemical adaptation to low light intensities
    • Light Independent Reaction (LIDR)
      • • The energy trapped from sunlight in the light dependent reaction (ATP and NADPH) is used to fix carbon from carbon dioxide into organic molecules.
      • • The reaction takes place in the stroma and is controlled by enzymes.
      • Ribulose bisphosphate carboxylase (Rubisco) allows carbon (carbon dioxide) to be fixed into an initial organic molecule
      • RBCase therefore can be seen as a link between inorganic (non-living) and the organic (living) e.g. Primary productivity
    • Light Independent Reaction
      • So-called because the reactions do not directly need light.
      • Occurs in the stroma of the chloroplast.
      • Fixes carbon to make carbohydrates.
    • The Calvin Cycle: Phases 1 & 2
      • 1. Carbon uptake
        • Adds carbon dioxide to 5C ribulose bisphosphate (RuBP)
        • Catalyzed into RUBISCO ; ribulose bisphosphate carboxylase
      • 2. Carbon reduction phase
        • Citrate is made and broken to form 2 phosphoglycerate (PGA)
        • PGA is rearranged and phosphorylated by ATP
        • NADPH reduces the backbone further to form glyceraldehyde-3-phosphate (G3P)
    • The Calvin Cycle: Phase 3
      • 3. Reformation of RuBP:
        • G3P is rearranged,
        • & phosphorylated
        • With further investment of ATP…
        • To make RuBP, a bisphosphorylated compound
      • Alternatively,
        • G3P is shuttled out of the cycle to produce glucose and other carbohydrates elsewhere
    • The Three phases of The Calvin Cycle LIR:
    • When RUBISCO Doesn’t Work
      • In high light and temperature:
        • Photosynthesis is very active
        • Water is easily lost
        • Leaf stomata close
        • Oxygen builds up
        • RUBISCO has mixed affinity for oxygen and CO 2
        • It binds O 2 when O 2 is abundant
        • G3P is NOT produced
    • Evolutionary “Work-Arounds” Avoid Photorespiration
      • 1. The C 4 pathway
        • Physically sequesters the carbon dioxide-requiring RUBISCO (carbon fixation) away from high oxygen
        • Uses compartmentation with biological membranes (in different cells)
        • In crabgrass, corn, and sugar cane
      • 2. Crassulacean acid metabolism (CAM)
        • Carries out C fixation separated in time from high temperature and high oxygen
        • In desert plants: succulents and cacti (also lilies and orchids)
    • C 3 versus C 4 Anatomy
      • Bundle sheath cells are arranged differently in C 3 and C 4 plants
    • C 4 Pathway
      • CO 2 is used by PEP carboxylase to convert phosphoenolpyruvate (3C) to oxaloacetate (4C)
      • Oxaloacetate is reduced to malate (4C)
      • Malate is transported via plasmodesmata to RUBISCO in the bundle sheath cell
      • Malate is degraded to CO 2 (1C) and pyruvate (3C), which is transported to the mesophyll cell
      • Pyruvate is phosphorylated to PEP by ATP
      • Takes 30 ATP per hexose, rather than 18 in C 3 ; used to regenerate PEP from pyruvate
    • Calvin cycle is all-important !
      • In C 3 , C 4 and CAM plants, the Calvin Cycle always receives the carbon dioxide that is made into carbohydrate...
      • . . . under all conditions! Reducing the effect of limiting factors
      • Scientists are very interested in getting C 4 chemistry genetically introduced into plants to increase crop efficiency.
    • Limiting Factors in the rate of Photosynthesis
      • • The rate of photosynthesis can be affected by light intensity, carbon dioxide concentration and temperature.
      • • Under a given set of conditions only one factor will affect the rate of photosynthesis this factor is at its minimum and is called the limiting factor .
      • • As has been shown photosynthesis is a process with many individual steps or stages.
      • • The overall rate of photosynthesis is determined by the step that is proceeding most slowly (rate-limiting step).
      • • Therefore each factor (e.g. light, temperature etc.) can become the limiting factor in any on the rate-limiting steps.
      • (a). As the concentration of CO 2 is increased the rate of photosynthesis increases.
      • (b).The concentration of CO 2 has saturated the process. The maximum rate of reaction has been achieved. Further increases in CO 2 do not increase the rate. The rate is now constant.
      • (c) Note this is the normal concentration of CO 2 in the atmosphere.! Therefore this is often the limiting factor.
      Carbon Dioxide (CO 2 )
    • Light intensity
      • As the intensity of light is increased the rate of reaction of photosynthesis increases. The rate maybe limited by a lack of NADP +
      • (b) Light intensity has saturated the plants. The rate now remains constant for any further increase in light intensity.
      • (c) Note that light intensity to achieve maximum rate of photosynthesis is less than the intensity of light in summer. Light in not normally a limiting factor
    • Temperature
      • The optimum temperature in a temperate climate is about 25° C.
      • • However. Temperature has many effects on a plant and the graph should be treated with caution.
      • • Temperature has just as many effects on respiration, transpiration and translocation all of which in turn affect photosynthesis.