ch 8 Flashcards
during photosynthesis, the ultimate electron donor is __.
water
The oxidation of water is linked with the reduction of carbon dioxide through a series of redox reactions making up the __.
photosynthetic electron transport chain
Photosynthesis is a __ reaction. During photosynthesis, CO2 molecules are reduced to form higher-energy __ molecules
redox; carbohydrate
Photosynthesis begins with the absorption of light by protein-pigment complexes known as __
photosystems
photosystems:
use absorbed light energy to drive redox reactions and thereby set the photosynthetic electron transport chain in motion. movement synthesizes ATP and NADPH
__ are the energy sources needed to synthesize carbohydrates from CO2 in the __.
ATP and NADPH; Calvin cycle
In the ocean, photosynthesis occurs in the surface layer about 100 m deep, called the __
photic zone
The __ proposes that the ancestor of the chloroplast was a free-living cyanobacterium that was engulfed by a eukaryotic cell.
endosymbiotic hypothesis
filling much of the center of the chloroplast is a third, highly folded membrane known as the __.
thylakoid membrane
Thylakoid membranes form structures that resemble flattened sacs, which are grouped into stacks called __.
grana
Within the grana is the __, and the area outside is the __.
lumen; stroma
Calvin Cycle step 1: carboxylation:
CO2 absorbed from the air is added to a 5-carbon molecule, ribulose-1, 5-bisphosphate (RuBP). reaction is catalyzed by rubisco (very slow enzyme). The 6-carbon molecule formed is broken down into two 3-carbon molecules of 3-phosphoglycerate (3-PGA)
__ is the reducing agent in the Calvin Cycle.
NADPH
> transfers the energy and electrons that allow carbohydrates to be synthesized from CO2
In the Calvin Cycle, the reduction of 3-PGA involves 2 steps:
1) ATP is used to phosphorylate 3-PGA
2) NADPH transfers two high-energy electrons to the phosphorylated compound
Calvin Cycle step 2: reduction:
For every six triose phosphate molecules that are produced, only one can be withdrawn from the Calvin cycle because ribulose-1,5-bisphosphate needs to be regenerated using the other triose phosphates
Calvin Cycle step 3: regeneration:
The 5-carbon molecule needed for carboxylation is regenerated. lots of reshuffling is required to produce three 5-carbon RuBP molecules from the five remaining 3-carbon triose phosphate molecules.
Calvin cycle regeneration: __ and __ are needed for each molecule of CO2 incorporated by rubisco.
Three NADPH; three ATP
Excess carbohydrates are converted to __ and stored
starch
Light is a type of __
electromagnetic radiation
The wavelengths of visible light are from __
400−700 nm
__ are molecules that absorb some wavelengths of visible light. __ look colored because they reflect light enriched in the wavelengths that they do not absorb.
pigments
Chlorophyll:
photosynthetic pigment, appears green. it has a large, light-absorbing head containing magnesium at its center and a long hydrocarbon tail that allows the pigment to be anchored in the lipid membrane
carotenoids:
orange/yellow
found in the thylakoid membrane, are able to absorb light from regions of the visible spectrum that are poorly absorbed by chlorophyll.
Absorption of __ by a chlorophyll molecule results in one of its electrons being elevated to a higher energy state
visible light
For isolated chlorophyll in the lab, most of the light energy absorbed by the electron is rapidly released as __ and some is reemitted as __.
heat; fluorescent light
chlorophyll in a photosystem absorbs light and __ the energy to another chlorophyll molecule, which then transfers the energy to another. The energy is passed from chlorophyll to chlorophyll until it reaches a specially configured pair of chlorophyll molecules known as the __
transfers; reaction center
The chlorophylls in the __ act as __, transferring absorbed energy from one to the other until it reaches a reaction center
thylakoid membrane; antenna
__ systems are necessary to provide enough energy to pull electrons from water and then use them to reduce NADP+.
2
Photosystem II:
supplies electrons to the beginning of the electron transport chain. When photosystem II loses an electron, it is able to pull another electron from water.
Photosystem I:
energizes the electrons with a second input of light energy, so they have enough energy to reduce NADP+.
Electrons pass between photosystem II and I through the
cytochrome b6f complex
Plastoquinone Pq vs plastocyanin Pc
Plastoquinone Pq carries electrons from photosystem II to the cytochrome b6f complex, while plastocyanin Pc carries electrons from the cytochrome b6f complex to photosystem I by diffusing through the thylakoid lumen
How do protons accumulate in the thylakoid lumen?
1) The oxidation of water releases protons and O2 into the lumen
2) the cytochrome b6f complex functions as a proton pump. As electrons transit through the complex, some of the energy that is released by each redox reaction is used to drive protons from the stroma side of the thylakoid membrane to the lumen
cyclic electron transport:
protects the cell from high energy electrons- electrons are shunted into an alternate pathway that increases the production of ATP while decreasing the production of NADPH. Electrons from photosystem I are redirected from ferredoxin back into the electron transport chain
antioxidant detoxification:
Antioxidants such as ascorbate, beta-carotene, and other antioxidants are able to neutralize reactive oxygen species.
Xanthophyll:
yellow-orange pigments that slow the formation of reactive oxygen by reducing excess light energy; these pigments accept absorbed light energy directly from chlorophyll and then convert this energy to heat
__ occurs when __ adds O2 instead of CO2 to RuBP, resulting in one molecule with three carbon atoms (3-PGA) and one molecule with only two carbon atoms
(2-phophoglycolate)
Photorespiration; rubisco
__ is theoretically around 4% of incoming solar energy, but actual yields are closer to 1% to 2%
Maximum photosynthetic efficiency
