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sWhat is the general chemical equaion for photosynthesis?
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Explain why photosynthesis is an example of a redox reduction.
- reduction: gain electrons, shifting of electrons towords atom
- oxidation: loses electrons, shifting of electrons away from atom
carbon is being reduced while oxygen is being oxidized
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Define Autotrophs.
organisms that make their own food (sugar) using sunlight by process of photosynthesis
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Where does photosynthesis occur in autotrophs?
plants and algae -> in chloroplasts
cyanobacteria -> cell membrane
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where does the light reaction of photosynthesis occur?
- light reaction produces ATP/NADP + H
- - it occurs at the thlakoid structure
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describe the roles of photosystems 1 and 2 in the light reaction.
Photosystem 2( produces ATP )
photosystem 1 produces NADPH,
- To begin photosynthesis, the chlorophyll molecule in photosystem II is
- excited by sunlight and the energy produced helps to break down a water
- molecule (H2O) into ½O2 (with electrons removed) and 2H+. The removed
- electrons are excited by the light energy. When the electrons prepare to
- come to their rest state, they go through an oxidative phosphorylation
- process and produces an ATP molecule.
- As the electrons are coming to a resting state, they are excited again
- in photosystem I and raised to a even higher energy state. The excited
- electrons are then used to produce NADP+ + H+. The highly energetic
- NADPH molecule is then fed into the Calvin Cycle to conduct carbon
- fixation.
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explain, in detail, the light reaction of photosynthesis.
- 1. As photons are absorbed
- by pigment molecules in the antenna complexes of Photosystem II, excited electrons
- from the reaction center are picked up by the primary electron acceptor of the
- Photosystem II electron transport chain. During this process, Photosystem II
- splits molecules of H2O into 1/2 O2, 2H+, and
- 2 electrons. These electrons continuously replace the electrons being lost by
- the P680 chlorophyll a molecules in the reaction centers of the Photosystem
- II antenna complexes.
- 2. During this process,
- ATP is generated by the Photosystem II electron transport chain and chemiosmosis.
- According to the chemiosmosis theory, as the electrons are transported down
- the electron transport chain, some of the energy released is used to pump protons
- across the thylakoid membrane from the stroma of the chloroplast to the thylakoid
- interior space producing a proton gradient or proton motive force. As the accumulating
- protons in the thylakoid interior space pass back across the thylakoid membrane
- to the stroma through ATP synthetase complexes, this proton motive force is
- used to generate ATP from ADP and Pi.
- 3. Meanwhile, photons are
- also being absorbed by pigment molecules in the antenna complex of Photosystem
- I and excited electrons from the reaction center are picked up by the primary
- electron acceptor of the Photosystem I electron transport chain. The electrons
- being lost by the P700 chlorophyll a molecules in the reaction centers
- of Photosystem I are replaced by the electrons traveling down the Photosystem
- II electron transport chain. The electrons transported down the Photosystem
- I electron transport chain combine with 2H+ from the surrounding
- medium and NADP+ to produce NADPH + H+.
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explain 3 ways the hydrgen ion concentration gradient across the thylakoid membrance is established.
- 1. splitting of water, generating H+
- 2. Add more H+, pumping of proton pumps
- 3. outside of stroma NADP+ picked up
- - reduce Hydrogen conc. difference in stroma
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Where exactly does the calvin cycle of photosynthesis occur?
stroma
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Explain how the calvin cycle reduces carbon dioxide to form sugar.
- RUBISCO attaches CARBON to RuBP
- First an enzyme (ribulose biphosphate carboxylase)
- causes carbon dioxide to combine with ribulose biphosphate (RuBP) to form
- a six-carbon compound that quickly decomposes to give two molecules of 3-phospho-glycerate
- (a three-carbon compound). Then, after being changed to glyceraldehyde 3-phosphate
- (G3P), this re-forms ribulose biphosphate with the release of the sugars
- fructose and glucose.
- These sugars are used in respiration
- or as a building block in making starch and
- cellulose
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