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Light Dependent Reaction
Photosystems­ The two groups of molecules that capture and transfer energy in the light dependent reaction.
The main function of the light dependent reaction is to capture and transfer energy.
­this involves the transfer of electrons.
­the energy from the electrons is used to make energy carriers like ATP and NADPH.
­These molecules are not used for energy for the cell, but are used in later stages of photosynthesis.
Photosystem II and the Electron transport chain have the first 3 steps and Photosystem I has the next 4.
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Photosystem II and Electron Transport
1. Chlorophyll in the thylakoid absorbs energy from the sunlight.
­the energy is transferred to electrons (e­)
­the high energy electrons leave the chlorophyll and enter the electron transport chain.
2. Water molecules split
­
3. Hydrogen Ions transported
­Electrons move from protein to protein in the electron transport chain.
­This energy is used to pump H+ ions against the concentration gradient into the thylakoid.
­Electrons move to Photosystem I
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Photosystem I
4. Energy absorbed from sunlight
­Chlorophyll absorbs energy from the sunlight
­Electrons are energized and leave the molecules
5. NADPH produced
­ Energized electrons are added to NADP+ (like ADP) and becomes NADPH (like ATP).
­NADPH goes to the light­independent reaction
Finally Production of ATP
6. Hydrogen Ion Diffusion
­ The H+ in photosystem II make a concentration gradient with the higher concentration of H+ ions outside of the thylakoid
­ this is called a chemiosmotic gradient and stores potential energy.
­The ions diffuse through a channel in the thylakoid
7. ATP Produced
­ATP synthase is an enzyme that makes ATP by adding a phosphate group to ADP.
­This is possible because of the diffusion of H+ ions.
Review
Oxygen, NADPH and ATP are produced
Oxygen is a waste product.
NADPH and ATP are used later to make sugars.
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Light­Independent Reaction
Does not need sunlight occur, but does occur in the chloroplasts
­Can take place anytime energy is available
­The energy source is the molecules of ATP and NADPH from the light dependent reaction
Calvin Cycle
­Uses carbon dioxide gas from the atmosphere and energy carried by ATP and NADPH to make simple sugars.
1. Carbon Dioxide is added
­ CO2 molecules are added to the 5 CO2 molecules already in the Calvin Cycle to make 6.
2. Three­carbon molecules form
­ATP and NADPH is used to split the 6 carbon molecules and rearranged into three­carbon molecules with higher energy.
3. Three­carbon molecules exit
­One high energy three­carbon leaves the cycle
­After two three­carbon molecules leave the cycle, they are bonded to build a six­carbon molecule GLUCOSE!
4. Three­carbon molecules recycled
­ATP is used to change the remaining three­
molecules back into five­carbon molecules and the cycle can begin again.
carbon Review
+ Products are a six­carbon molecule (like Glucose), NADP
and ADP.
NADP+ and ADP return to light­dependent reactions.
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Functions of Photosynthesis
Photosynthesis is important to Earth's environment and to Earth's organisms.
Photosynthesis produces food for themselves and other organisms.
Both plants and animals will release the stored energy in food through cellular respiration.
­This process uses the oxygen produced as waste product of photosynthesis.
Photosynthesis also provides materials for plant growth and development.
Photosynthesis also helps to regulate Earth's environment by removing carbon dioxide from the Earth's atmosphere.
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