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The Reactions of Photosynthesis
Transcript of The Reactions of Photosynthesis
take place in the thylakoid membranes and involve the photosystems B. Electron Carriers a) when sunlight hits chlorophyll molecules, some of their electrons become excited (have high-energy)
b) excited electrons leave chlorophyll and are transported by electron carriers to other molecules 1) electron transport chain: the series of electron carrier molecules that transport electrons
2) NADP+: one of the electron carriers
NADP+ + 2e- + H+ NADPH
3) NADPH: a high-energy molecule that provides energy to make many molecules including glucose C. Light Dependent Reactions a) the following are the steps of the light dependent reactions of photosynthesis 1) chlorophylls of photosystem II absorb light energy 3) the electrons are passed through the electron transport chain to photosystem I 5) the 2 electrons replace those lost from a chlorophyll 7) some of the hydrogen ions move inside the thylakoid (energy comes from the moving electrons) 9) these electrons are passed through a second electron transport chain to NADP+ b) net result: water was used, NADPH, ATP, and oxygen were made D. The Calvin Cycle a) Calvin Cycle: another name for the light independent reactions; makes high-energy sugars (glucose) 1) named after Melvin Calvin who uncovered the reactions of the cycle b) must have the energy from NADPH and ATP from the light dependent reactions to work
c) steps of the Calvin Cycle: 1) 6 CO2 molecules enter the cycle 3) this produces 6 molecules each with 6 carbons 5) the 3 carbon compounds are converted into higher energy 3 carbon compounds 7) the other 10 are converted back into 6 molecules of the 5 carbon compounds (of step 2) d) net result: 6 CO2 molecules were used to make 1 glucose E. Factors Affecting Photosynthesis a) many factors affect the rate of photosynthesis including: 1) lack of water - slows/stops it; plants in dry areas reduce water loss in a waxy coating on leaves
2) high or low temperatures - slows/stops it
3) increasing the light level increases the rate of photosynthesis until a maximum rate is reached a) chloroplasts: the plant organelle containing chlorophyll where photosynthesis occurs 2) thylakoid: a saclike structure; its membrane contains the chlorophyll 3) granum: a stack of thylakoids (grana is the plural - refers to more than one stack 4) photosystem: a cluster of chlorophyll molecules organized into a light-collecting unit
photosystem II: 1st set of chlorophylls that absorb light (II because it was discovered second)
photosystem I: 2nd set of chlorophylls that absorb light (I because it was discovered first) 2) light independent reactions: the reactions of photosynthesis not requiring the presence of light
also called the Calvin Cycle
take place in the stroma
require substances made by the light dependent reactions to occur 2) each chlorophyll loses 2 electrons 4) enzymes of the thylakoid membrane split the water into 2 hydrogen ions, 2 electrons, and 1 oxygen 6) the oxygen joins with another to become the oxygen of the air 8) the 2 electrons at photosystem I are reenergized by light 10) NADP+ plus the 2 electrons and 1 hydrogen ion join to make NADPH 11) hydrogen ions on the inside move through a membrane protein providing energy to make ATP 2) they join with 6 molecules that each have 5 carbons 4) they split into 12 molecules each with 3 carbons 6) Two or three of the carbon compounds join to make glucose (which has 6 carbons) or some other substance