Captures light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules. Photosynthesis nourishes almost all the living world directly or indirectly.
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Autotrophs
produce organic molecules from CO2 and other inorganic raw materials obtained from the environment.
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Heterotrophs
live on organic compounds produced by other organisms. ( also fungi and prokaryotes)
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Major sites of photosynthesis in most plants
Leaves
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Mesophyll
The interior of the leaf, where most chloroplasts are found
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Stomata
microscopic pores in the leaf
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Parts of a chloroplast
inner, outer, and inter membrane, lamella, lumen, thylakoid, stroma, grana/granum
uses energy from light reactions to make CO2 into sugar
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photophosphorylation.
generating ATP using chemiosmosis
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Do light reactions produce sugar?
No, that only happens in the Calvin Cycle
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carbon fixation
beginning of carbon cycle, involves incorporating CO2 into organic molecules
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light-independant/dark-cycle
metabolic reactions that don't intrinsically require light
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light
form of electromagnetic energy or radiation
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electromagnetic spectrum.
entire range of electromagnetic radiation
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visible light
narrow band between 380 and 750 nm, visible to human eye
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photon
particle of light
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Visible light
radiation that drives photosynthesis
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spectrophotometer
measures the ability of a pigment to absorb various wavelengths of light.
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absorption spectrum
plots a pigmentâs light absorption versus wavelength.
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Chlorophyll a
which participates directly in the light reactions, absorbs best in the red and violet-blue wavelengths and absorbs least in the green.
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Chlorophyll b
has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a
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Carotenoids
can funnel the energy from other wavelengths to chlorophyll a and also participate in photoprotection against excessive light
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photosystem
composed of a reaction-center complex surrounded by several light- harvesting complexes.
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reaction-center complex
organized association of proteins holding a special pair of chlorophyll a molecules.
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light-harvesting complex
pigment molecules (which may include chlorophyll a, chlorophyll b, and carotenoids) bound to proteins.
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primary electron acceptor,
accepts an excited electron from the reaction center chlorophyll a.
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Photosystem naming
in order of discovery, not in order of when they work
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PSII(Photosystem 2)
has a reaction-center chlorophyll a known as P680, with an absorption peak at 680 nm.
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PSI(Photosystem 1)
has a reaction-center chlorophyll a known as P700, with an absorption peak at 700 nm.
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Linear electron flow
Drives synthesis of ATP and NADPH
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light reactions part 1
look at the picture
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light reactions part 2
look at the picture
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ATP Synthase
used same as in a normal cell
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Where do the protons for the gradient come from?
water
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G3P
actual product of Calvin Cycle
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carbon fixation phase,
Each CO2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP)
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rubisco
Rubisco is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. Used to catalyze carbon fixation
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reduction
3-phosphoglycerate receives another phosphate group from ATP to form 1,3-bisphosphoglycerate. These are then reduced into 6 G3P, which ends up into a net gain of carbohydrates. Other five are recycled to regenerate RuBP
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regeneration
carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle to regenerate three molecules of RuBP. 3 more molecules of ATP are spent, it makes RuBP prepared to receive CO2
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What is a main issue for plants?
dehydration
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main site of water loss
stomata
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What do plants do with stomata on dry days, and what does this lead to?
They close their stomata, and it leads to a large buildup of oxygen and less increase in CO2 taken in
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photorespiration.
consumes ATP and doesnt produce sugar. Originally thought to be some kind of evolutionary baggage.
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C4
fix CO2 in a four-carbon compound
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Bundle-sheath cells
arranged in tightly packed sheaths around the veins of the leaf
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C4 photosynthesis does what?
minimizes photorespiration and improves sugar production
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CAM
crassulacean acid metabolism,
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CAM plants
store the organic acids they make during the night in their vacuoles until morning, when the stomata close
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Differences between CAM plants and C4 plants
In C4 plants, carbon fixation and the Calvin cycle are structurally separated. In CAM plants, carbon fixation and the Calvin cycle are temporally separated. Both use Calvin Cycle