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PhotosynthesisChapter 8
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Light & Color
Primary colors of light: red, green, blue White light = equal “amounts” of red, green, and
blue Pigments absorb certain colors of light and reflect
others Primary colors of pigment: yellow, cyan, magenta
Black = equal amounts of yellow, cyan, and magenta White = no pigment
Sun produces white light Objects appear the color of the wavelength of light
they reflect
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Plant Pigments
Plants contain a number of pigments, yielding a variety of colors and shades Chlorophyll a is the primary pigment involved in
photosynthesis Blue-green in color
Accessory pigments = all other pigments
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The Chloroplast
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Chlorophyll and Photosystems
Chlorophyll is embedded in the thylakoid membrane
Photosystem = collectionof pigments inthylakoid membrane
Photosystems captureenergy from the sun tocarry out reactions ofphotosynthesis
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Overview of Photosynthesis
Overall equation:
12 H2O + 6 CO2 6 H2O + 6 O2 + C6H12O6
Photosynthesis is a two-stage process: The Light Reactions
Hydrolyze water to obtain electrons and produce ATP and NADPH, oxygen is a waste product
The Calvin Cycle Products of the light reactions power this stage to
create sugar from carbon dioxide
lightenergy
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The Light Reactions
1. Water is hydrolyzed by chlorophyll a when excited by light – Photosystem II
Electrons are liberated Two split waters = one oxygen molecule
2. Electrons pass through a series of proteins in the thylakoid membrane producing ATP
Electron Transport Chain
3. Electrons used to reduce NADP+ into NADPH – Photosystem I
NADPH is an electron carrier that delivers electrons to the Calvin Cycle
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The Light Reactions
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The Calvin Cycle
1. Carbon dioxide is fixed to RuBP (ribulose biphosphate), a 5-carbon molecule
Catalyzed by RuBisCO
2. Newly created 6-carbon molecule with two phosphates splits apart
3-carbon molecules created
3. ATP hydrolyzed to phosphorylate the 3-carbon molecule
4. NADPH is oxidized to NADP+ when it reduces the 3-carbon molecule
End product is a 3-carbon sugar = Glyceraldehyde 3-phosphate
(G3P)
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The Calvin Cycle
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Photosynthesis Animation
(view animation file on public server)
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Arid Environments & Carbon Fixation
Plants close stomata on hot, dry days to avoid dehydration In leaf, CO2 level falls, O2 level rises Rubisco attaches oxygen to RuBP =
photorespiration C4 and CAM plants use alternative methods for
carbon fixation
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C4 and CAM Plants