Biology 111- Week 7: Photosynthesis
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- Where does photosynthesis occur?
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at the cell level, in chloroplasts
at the organism level, in leaves and stems - What is the formula for photosynthesis?
- CO2 + H2O = C6H12O6 + O2 + H2O
- Which chemical rxn is used in photosynthesis?
- endergonic/anabolic rxn
- What are the components of a leaf?
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*lipid cuticle
*stomata
*upper and lower epidermis
*palisade layer
*spongy layer
*vein - What is the purpose of the lipid cuticle?
- to resist desication
- What is the purpose of the stomata?
- the external pit, or pore, is used for gas exchange
- What are the upper and lower epidermis?
- outer cell layers
- What is the function of the palisade layer?
- primary site of photosynthesis
- What is the function of the spongy layer?
- gas "storage"
- What does the vein do?
- carries carbohydrates/water/minerals
- What are the parts of chloroplast?
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*outer and inner membranes
*thylakoid- the embedded pigments
*grana- the stack of thylakoids
*stroma- the internal fluid - How what ways does light exist?
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in packets of energy- photons
as waves of energy- wavelength - What are the types of wavelengths?
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*short= high energy
ie. gamma, x-rays, ultra violet
*long= low energy
ie. radio, microwaves, infra red - What are the colors of light and how are they measured?
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(short) V I B G Y O R (long)
they are measured in nanometers - What happens to light?
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*absorbed- by pigments in the thylakoid and used to drive chemical rxns
*reflected- bounced back into space as the color we see
*transmitted- passes through substances - What are pigments?
- substances that absorb visible light
- What is an absorption spectrum?
- a graph plotting a pigment's light absorption versus the wavelength
- What are the types of pigments which absorb light to drive photosynthesis?
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*chlorophyll A- blue/green
*chlorophyll B- yellow/green
*accessory pigments:
-carotenoids- yellow/orange
*phycocyanins - What are photosystems?
- light harvesting areas of the thylakoid membrane
- What is the light-harvesting complex made of?
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*chlorophyll
*proteins
*other kinds of molecules
*an antenna consisting of a few hundred pigment molecules - How does the antenna complex of the photosystem work?
- When an antenna molecule absorbs a photon, the energy is transmitted from pigment molecule to pigment molecule until it reaches a particular chlorophyll a located in the rxn center.
- What is P700?
- the rxn center chlorophyll A pigment of photosystem I that absorbs light in the 700nm part of the wavelength (the far red part
- What is P680?
- the rxn center chlorophyll A pigment of photosystem II that absorbs light in the 680nm part of the wavelength (also in the red part)
- What is the difference of P680 and P700?
- each associates with different proteins in the thylakoid membrane, affecting electron distribution to cause slightly different light-absorbing properties
- What does each photosystem consist of?
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*light harvesting antenna complex
*300 chlorophylls
*accessory pigments
*primary electron acceptor in the rxn center: P680 and P700
*electron transfer chain/proton pump - What is the relation of photosystems (I and II) to thylakoids?
- each thylakoid contains thousands of photosystems
- During light rxns of photosynthesis, what are the two possible routes for electron flow that generates ATP?
- cylic and noncyclic photophosphorylation
- What is noncyclic electron flow?
- the path the electrons take to generate ATP and NADPH
- What is non-cyclic photophosphorylation?
- ATP synthesis during noncyclic electron flow
- What is cyclic electron flow?
- an alternative path taken by electrons that uses only photosystem I, where there is no production of NADPH and no release of oxygen, though ATP is still generated
- What is cyclic photophosphorylation?
- ATP synthesis during cyclic electron flow
- What are the key components of light rxns?
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*two photosystems
*two electron transport chains
*ATP synthase - How does the photosystem II work?
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1. Photosystem II -noncyclic phototphosphorylation- starts its process when light energy reaches P680
2. 2 electrons are excited to a primary electron acceptor
3. 2 electron "holes" are filled in P680 by splitting water- leaving H+ and O2
4. electrons are passed through a series of molecules with energy being released at each step (this is the electron transport chain)
5. the energy is used to pump hydrogen ions from the stroma into the thylakoid compartment, creating a concentration gradient
6. the electrons are sent on to fill the "holes" in Photo I - How does the photosystem I work in noncyclic photophosphorylation mode?
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1. photosystem I receives energy from radiant energy
2. electrons in P700 are excited to a primary electron acceptor
3. electrons are passed through an electron transport chain and are added to NADP+ to form NADPH
4. the "holes" are filled with the electrons passed on from Photo II - How does photosystem I work when in cyclic photophosphorylation mode?
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1. photosystem I receives energy from itself (end of the cycle) and radiant energy
2. electrons in P700 are excited to a primary electron acceptor
3. electrons are passed through an electron transport chain and sent back
4. so the "holes" are filled with the electrons it sent back to itself - How does the hydrogen pump work?
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1. Energized electrons from photosystem II are passed through another electron transport chain. Their energy is used to pump hydrogen ions (H+) from the stroma into the thylakoid compartment, creating a concentration gradient.
2. The buildup of hydrogen ions inside the thylakoid compartment stores potential energy. This energy is harvested by an enzyme called ATP synthase.
3. As hydrogen ions diffuse through ATP synthase, down their concentration gradient, the enzyme uses the energy of the moving ions to make ATP.
(Next, ATP and NADPH are used in the sugar-making process of the Calvin cycle.) - What is chemiosmosis?
- coupled processes occurring in the electron transport chain + the hydrogen pump