Transcript Photosynthesis

Photosynthesis
Chapter 7
Photosynthesis
• Occurs in green plants, algae, and some
bacteria
• Transforms light E into chemical E
– Stored in sugar bonds
• Also produces O2
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
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
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
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
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
Light Capturing
• In thylakoids
• Electron transfer chain in photosystem
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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
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?
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
Review of Photosynthesis