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Photosynthesis
process in plants of breaking down carbon dioxide and oxygen into glucose with he assistance of sunlight
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Chlorophyll "a"
main type of chlorophyll that all plants have
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Accessory pigments
- absorb energy that chlorophyll "a" does not absorb
- such as chlorophyll b, c, d, e
- carotenoids (blood orange)
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Different pigments' purpose
- to absorb different waves of energy
- different pigments absorb different, specific kinds of energy
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Leaves in autumn
change colour because the light is received by the leaf at a different angle, therefore different wavelengths/colours are absorbed by the leaf
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Senescence
- trees talking using hormones
- why all trees' leaves change colour at same time
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Chlorophyll
pigment/colour
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Xylem
- dead cells/tissue
- transports water
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Phloem
- living cells
- transports sugars
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Cuticle, epidermis
- prevent water loss
- Cuticle is waxy, wax is an oil, water cannot escape past this oily waxy layer of the leaf
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Palisade mesophyll cells
contain chloroplasts
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Thylakoid
- system of interconnected flattened membrane sacs
- stack on top of each other, forming grana (multiple thylakoids stacked)
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Lamellae
structural support
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Photosynthesis
- occurs in thylakoid, stroma
- thylakoid: light dependent reactions, has pigment, traps light, so light is used
- stroma: light independent reactions, does not need any light
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ATP role
splits H2O, CO2, to make glucose (energy)
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NADPH
- holds electrons, gives electrons to something else
- made of an NADP, and an H
- NADP is positively charged, therefore bonds with two e- to balance out
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Photosynthesis stages
- 1. capture solar energy and transfer it to e-
- 2. use captured solar energy to make ATP; transfer high energy e- to NADP+: NADPH is then used as a high energy e- carrier
- 3.
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Reactants of photosynthesis are the products of
cellular respiration
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Light independent stage (stage 3 of photosynthesis)
- occurs during either day or night
- a.k.a. Calvin cycle
- carbon fixation occurs: incorporation of CO2 into organic compounds such as glucose
- occurs in stroma or chloroplast
- uses ATP and NADPH from light dependent reactions
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Stroma
gel-like fluid inside of chloroplast
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Capturing solar energy (stage 1 of photosynthesis)
- occurs in thylakoid membranes
- cluster of chlorophyll and other pigments
- photosystem 1 uses chlorophyll "a"
- photosystem 2 uses a slightly different form of chlorophyll "a"
- photosystems operate so that a wide range of wavelengths can be used for photosynthesis
- photosystem 2 occurs first, then photosystem 1 occurs second
- 2 energized e- are removed from photosystem 2 from chlorophyll
- e- enters an electron transfer chain
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Photosystem
- areas where light is being captured
- photosystem 2 makes NADPH
- photosystem 1 makes ATP
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Redox
- any time when an electron is moved
- ANY
- A N Y
- literally any time
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Electron transfer chain
- hot potato, basically of electrons
- ATP is made because of the energy release through the chain
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Photolysis
- occurs in thylakoid lumen
- literally "light cut"
- solar energy absorbed by chlorophyll is used to split water into H, e-, O2
- e- travels to photosystem 2
- O exits thru stomata or is used to make H2O
- H will be used later to reduce ADP
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Electron transfer and ATP synthesis events
- a) e-, excited by light at photosystem 2, are passed along an ETC
- e- releases energy at every step
- b) energy from e- is used to pull H+ ions across membrane into lumen
- e- have lost most of their energy
- H+ ion concentration builds up and so does a positive charge
- c) e- are transferred from ETC to photosystem 1
- d) e- are transferred to NADPH
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Chemiosmosis
- diffusion based on concentration of positive Hydrogen ions (high to low)
- electrical gradient results
- H+ ions rush through ATP synthase complex
- in doing so, H+ ions generate energy
- this energy is used to create ATP
- this energy in H+ ions comes from the sun originally
- ATP synthase complex is in the thylakoid membrane
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Light independent reactions
- happens in stroma
- Calvin-Benson cycle and carbon fixation
- carbon fixation = turning CO2 into glucose
- upon entering Calvin cycle, carbon is reduced
- direct product of Calvin cycle is G3P/PGAL, precursor to glucose
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Stage 3: Light independent reactions continued
- C, O atoms provided by CO2
- H atoms provided by photolysis of H2O
- 3 ATP, 2 NADPH are used per each CO2 that enters the Calvin cycle
- the building of one glucose molecule requires 18 ATPs, 12 NADPHs
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Stages of Calvin cycle/carbon fixation
- 1. CO2 fixation, reduction
- 2. PGAL/G3P molecules produced
- 3. regeneration of RUBP
- each stage requires enzymes to occur
- RUBP + CO2 -> unstable 6 - C molecule
- 6 - C molecule breaks down into two 3 - C molecules (PGA)
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Calvin cycle step 1
- RUBP (ribulose biphosphate) 5 carbon molecules long, attaches to CO2
- enzyme for this reaction is RUBP carboxylase
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Calvin cycle step 2
- each 3 PGA molecule gets reduced; ATP and NADPH provide this step
- 3 C PGA is reduced to form PGAL and water
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Calvin cycle step 3
- direct product - PGAL
- glucose: six revolutions of Calvin cycle required for one molecule of glucose
- 6 H2O
- (ADP, P, NADP+, H+) - products of photosynthesis
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Lumen
space inside of thylakoid itself
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Final electron acceptor in ETC
O2
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