Rebecca Davenport 10 24 16 BIOL 1406 BW1 Ch 10 blueprint 1 Part 1 Photosynthesis the process that converts solar energy into chemical energy a Photo light Synthesis to build photosynthesis uses light energy to build sugars b Why is photosynthesis important i Directly or indirectly photosynthesis nourishes almost the entire living world c Where does it occur chloroplasts i In plants algae certain other unicellular eukaryotes and some prokaryotes ii Does NOT occur in just plants d e Chemical reaction of photosynthesis i 6 CO2 12 H2O Light energy C6H12O6 6 O2 6 H2O ii Chloroplasts split H2O into hydrogen and oxygen incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by product iii Reverses the direction of electron flow compared to respiration iv Redox process in which H2O is oxidized and CO2 is reduced v Endergonic process the energy boost is provided by light vi ix Purpose Stage xii Input xv output xviii f location vii x Light energy viii Light reactions xi linear electron flow xiii Light energy xiv photon water xvi ATP O2 oxygenxvii is waste NADPH xix Thylakoid xx membrane xxi Two stages of photosynthesis i Light reactions the photo part To build sugar Calvin cycle CO2 1 G3P Stroma 1 Occurs in the thylakoid membrane 2 Split H2O Release O2 3 Reduce the electron acceptor NADP to NADPH 4 Generate ATP from ADP by photophosphorylation ii Calvin cycle the synthesis part 1 In the stroma 2 Forms sugar from CO2 using ATP and NADPH 3 Begins with carbon fixation incorporating CO2 into organic molecules 4 Requires both NADPH and ATP g Site of photosynthesis in plantsi Leaves and other green areas are the major locations of photosynthesis ii Chloroplasts are found mainly in cells of the mesophyll the interior tissue of the leaf 1 iii CO2 enters and O2 exits the leaf through microscopic pores called stomata iv A chloroplast has an envelope of two membranes surrounding a dense fluid called the stroma v Thylakoids are connected sacs in the chloroplast which compose a third membrane system stacks grana vi Chlorophyll the pigment which gives leaves their green color resides in the thylakoid membranes vii 2 Autotrophs sustain themselves without eating anything derived from other organisms a Producers make organic molecules from CO 2 and other inorganic molecules b Photoautotrophs use the energy of sunlight to make organic molecules i Carbon source is CO2 3 Heterotrophs obtain their organic material from other organisms a Heterotrophs are the consumers of the biosphere b Almost all heterotrophs including humans depend on photoautotrophs for food and O 2 c d 4 Part 2 Nature of light a The Nature of sunlighti Light travels in rhythmic waves ii Wavelength is the distance between crests peaks of waves iii The electromagnetic spectrum is the entire range of electromagnetic energy iv Visible light consists of wavelengths that produce colors we can see v vi Photons are quantities of light energy b Photosynthetic pigments The light receptors i Pigments are substances that absorb visible light ii Different pigments absorb different wavelengths iii Wavelengths that are not absorbed are reflected or transmitted iv An absorption spectrum is a graph plotting a pigment s light absorption versus wavelength v An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process c Pigments i Chlorophyll a is the main photosynthetic pigment ii Accessory pigments such as chlorophyll b broaden the spectrum used for photosynthesis iii Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll photoprotection d Excitation of chlorophyll by light i When a pigment absorbs light it goes from a ground state to an excited state which is unstable e 5 Part 3 Light Reactions a Photosystem consists of a reaction center complex a type of protein complex surrounded by light harvesting complexes i The light harvesting complexes pigment molecules bound to proteins transfer the energy of photons to the reaction center ii Water is considered source of energy b Linear electron flow the primary pathway involves both photosystems and produces ATP and NADPH using light energy i Two possible routes for electron flow 1 Cyclica Electrons cycle back from Fd to the PS I reaction center b Uses only photosystem I and produces ATP but not NADPH c No oxygen is released d May protect cells 2 Linear a b Water is source of all electrons c KNOW WHICH IS P680 AND P700 ii v viii Photosystems iii Light iv Reaction harvesting complex center vi Pigments and vii Primary carotenoids electron acceptor ix x Pair of special chlorophyll molecule xi 8 steps involving two photosystems and two electron transport chains xii 6 Part 4 Calvin cycle a Regenerates its starting material after molecules enter and leave the cycle b Builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH c Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3 phospate G3P d For net synthesis of 1 G3P the cycle must take place three times fixing 3 molecules of CO2 e The Calvin cycle has three phases i Carbon fixation taking carbon from CO2 and attaching it to other molecules 1 CO2 attached to a 5 carbon molecule RuBP using the enzyme Rubisco to get 2 molecules of 3 phosphoglycerate 2 RuBP CO2 Rubisco 3 Phosphoglucerate ii Reduction 1 3 phosphoglycerate gets phosphorylated and reduced loses its phosphate group to become G3P 2 For every three CO2 that enter the Calvin Cycle 6 G3P are made but only one exits 3 Uses 6 ATP and 6 NADPH iii Regeneration of the CO2 acceptor RuBP 1 Carbon skeletons of 5 G3P rearranged to form 3 RuBP 2 Requires 3 ATP f iv Alternative mechanisms of carbon fixation i Dehydration is a problem for plants sometimes requiring trade offs with other metabolic processes especially photosynthesis ii On hot dry days plants close stomata which conserves H 2O but also limits photosynthesis iii The closing of stomata reduces access to CO2 and causes O2 to build up iv These conditions favor an apparently wasteful process called photorespiration 1 Photorespiration a In most plants C3 plants initial fixation of CO2 via rubisco forms a three carbon compound 3 phosphoglycerate b In photorespiration rubisco adds O2 instead of CO2 in the Calvin cycle producing a two carbon compound c Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar d v In relation to Photosynthesis 1
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