Photosynthesis L8-11 Flashcards
What is chlorophyll? Where is it located
A specialized light absorbing green pigment - located inside chloroplasts inside mesophyll cells
Is photosynthesis efficient?
Not very - only 4% of sunlight is used
Define photosynthesis
The process of transforming light energy into usable energy (ATP/NADPH) which is then stored in chemical bonds of carbohydrates
Describe why leaves are optimal organs for light absorption
They have a thin cross section and flat surface which allow for a cell organization that maximizes light capture/gas exchange and take little energy to produce
How much of the light spectrum can plants use?
The visible light spectrum only
What portion of the light spectrum is absorbed by chlorophyll?
Blue and red (400-450/650-700)
What pigments absorb the rest of the light if chlorophyll doesnt?
Bacteriochlorophyll
Chlorophyll a
Chlorophyll b
phycoerythin
beta-carotene
What are the 2 groups of pigments other than chlorophyll, and briefly summarize them
Carotenoids- accessory pigments that absorb between 400-500, anti-oxidant properties and prevent light damage (photo-protective role)
Bilin pigments
Accessory pigments
absorb between 400-500
How does chlorophyll absorption work?
It absorbs light photons which changes its energy state
Blue light excites chlorophyll more than red light
the excited state makes the pigment unstable
After absorption by chlorophyll what are the routes the energy may go
Heat-energy loss
Re-emittance of longer wavelength - fluorescence
Energy transfer- resonance transfer
Photochemistry- absorption with electron transfer
Summarize chloroplast anatomy
Relatively large
One circular chromosome
Arise from pre-existing chloroplasts or precursor proplastids
3 Membranes
What are the 3 membranes in chloroplasts
Outer- relatively permeable & contains porins
Inner - Very impermeable, requires transporters
Thylakoid- site of light reactions, contains integral proteins and pigments
What are the four protein complexes within the thylakoid membrane and what is their arrangement?
Photosystem 2
Cytochrome b6f complex
Photosystem 1
ATP synthase
They have a vectorial arrangement
Define resonance transfer
Vibrational transfer which passes energy down the energy gradient from pigments to reaction center chlorophyll - used for light absorbed by accessory pigments
What is the importance of P680+?
It is the strongest oxidizing agent in biological systems
Quickly summarize the difference between PS 1 and PS 2
in PS 2 Water is split and oxygen is released, it is a part of non cyclic electron flow
Cyclic electron flow uses only PS1
Summarize non cyclic electron flow
Z- scheme
5 steps
photo absorbtion
oxidation of water
ETC p1
ETC p2
Photophosphorylation
Uses both photosystems
Splits H20
What does the non-cyclic pathway produce?
Equal amounts ATP and NADPH
Briefly summarize cyclic electron flow
No water and no oxygen used
ATP produced
Electron from P700 moves to ferredoxin and is then transfered into PQ and CYTb6f
transferred into lumen and replace with plastocyanin
then generates ATP through ATP synthase in protein gradient
What are carbon reactions?
Reactions indirectly regulated by light
Allows photoautotrophic organisms to reduce CO2 to CH2O
Converts chemical energy to stored energy within carbohydrates
Occur in chloroplast stroma
What are the 3 phases of the carbon reactions?
Carboxylation
Reduction
RuBp regeneration
What are the products of the carbon reaction?
6 G3P molecules/ 3CO2 used
Where do the 6 G3P molecules from carbon reactions go?
5 are used for RuBP regeneration
1 is used to produce sugars and starch
Define retrograde regulation
Plastid controls nucleus
Define anterograde regulation
Nucleus controls plastid
