photosynthesis chapter 7. photosynthesis occurs in green plants, algae, and some bacteria transforms...
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Photosynthesis
Chapter 7
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Photosynthesis
• Occurs in green plants, algae, and some bacteria
• Transforms light E into chemical E– Stored in sugar bonds
• Also produces O2
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Anatomy of a Leaf
• Exterior of stoma (pl. stomata) for gas exchange• Veins carry water from roots and sugars from leaves• Mesophyll is interior leaf tissue– Filled with chloroplasts, site of photosynthesis
• Stroma, thylakoids with chlorophyll, grana
– All green areas of plants, concentrated in leaves
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The Electromagnetic Spectrum• Electromagnetic (light)
energy travels in waves– Wavelength from crest to crest
• Energy levels vary– Low energy = long waves
• Microwaves, radio waves– High energy = short waves
• Gamma rays, x-rays– Visible spectrum
• Colors seen are those that are reflected, not absorbed– White reflects all light– Black absorbs all light– Green plants reflect green
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Light Energy• Exists as photons, discrete units of
energy• Pigments absorb specific photons – Energy elevates e-s of pigments to
higher orbital ( PE)
• Unstable in upper orbital so ‘fall’ back quickly– Releases energy as heat
• White vs black cars/clothing in the South
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Plant Pigments• Leaves contain a variety of pigments– Chlorophyll a: reflects green
• Direct photosynthetic reaction– Chlorophyll b: reflects green
• Absorbs E and transfers to chlorophyll a– Carotenoids: reflects yellow and orange
• Behaves like chlorophyll b• Expand system capabilities
– Photoprotection: absorbs excess E to prevent damage– Similar mechanism in retina “Carrots for good eyes”
– Anthocyanins: reflects red and purple• Cherries and flowers
• Fall foliage change b/c other pigments outlast chlorophyll’s
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Overview of Photosynthesis• Light reaction
– In the thylakoids– Light E to ATP and NADPH
• Fuels the dark cycle– Oxygen atoms escape
• Dark reaction– In the stroma– Assembles sugars
• Carbon fixation: incorporate CO2 to organic compounds
– NADPH reduces carbon• Electron mov’t?
– ATP provides chemical E to run the cycle
– No direct need for light
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Light Capturing• In thylakoids• Electron transfer chain in photosystem– Clusters of chlorophyll, pigments, and proteins– Light-gathering “antennae”– Photosystem I (P680)—absorbs red light at 680nm– Photosystem II (P700)—absorbs far-red light at 700nm
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Light-Dependent (Light) Reaction
• Starts with:– Sunlight – Water
• Ends with:– ATP and NADPH
• Important products in this process:– Oxygen
• e-’s from water to PS II/PS I to NADP+
– ETC between photosystems set up [H +] gradient in thylakoid space
– H + out to stroma through ATP synthase• Photophosphorylation
• Where do you recognize this process from?
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Light-Independent (Dark) Reaction
• Starts with:– 6 CO2
– ATP and NADPH• Ends with:– 2 G3P (3C) = sugar
precursor• Important products in this
process:– NADP+ and ADP + Pi
– 3 RuBP
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Review of Photosynthesis