PHOTOSYNTHESIS* A.***PHASE*1.* - Steinbach Science · 2014-03-05 · PHOTOSYNTHESIS*!...
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PHOTOSYNTHESIS A. PHASE 1. Light'Dependent Reactions (phase of photosynthesis where light energy is converted to chemical energy in the form of ATP; results in the splitting of water and the release of oxygen) 1. Sunlight strikes the chlorophyll molecules in the thylakoid membrane; the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain (series of proteins embedded in a membrane along which energized electrons are transported; as electrons are passed from molecule to molecule, energy is released), a series of proteins embedded in the thylakoid membrane. a. Each protein in the chain passes energized electrons along from protein to protein, similar to a bucket brigade in which a line of people pass a bucket of water from person to person to fight a fire. At each step along the transport chain, the electron loses energy, just as some of the water might be spilled from buckets in the fire' fighting chain. b. The electron transport chain allows small amounts of the electron’s energy to be released at a time. This energy is used to form ATP from ADP, or to pump from ADP, or to pump hydrogen ions into the center of the thylakoid disc. After the electron has traveled down the first electron transport chain, it is passed down a second electron transport chain. 2. Following the second electron transport chain, the electron is still very energized. So that this energy is not wasted, the electron is transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP + (nicotinamide adenine dinucleotide phosphate, electron carrier molecule; when carrying excited electrons it becomes NADPH) is used. 3. When carrying the excited electron, NADP + combines with a hydrogen ion, H + , and becomes NADPH. NADPH will play an important role in the formation of carbohydrates later. Restoring Elections To Chlorophyll 4. Although some of the light'energized electrons may be returned to chlorophyll after they’ve moved through the electron transport chain, many leave with NADPH for the light' independent reactions. If these electrons are not replaced, the chlorophyll will be unable to absorb light and the light'dependent reactions will stop, as will the production of ATP. To replace the lost electrons, molecules of water are split. 5. Each molecule of water produces one'half molecule of oxygen gas, two hydrogen ions, and two electrons. This process is called photolysis (reaction taking place in the thylakoid membranes of a chloroplast during lightBdependent reactions where two molecules of water are split to form oxygen, hydrogen ions, and electrons). The oxygen of photolysis supplies the oxygen we breath.
Transcript of PHOTOSYNTHESIS* A.***PHASE*1.* - Steinbach Science · 2014-03-05 · PHOTOSYNTHESIS*!...
PHOTOSYNTHESIS*!
A.***PHASE*1.*Light'Dependent!Reactions!(phase&of&photosynthesis&where&light&energy&is&converted&to&chemical&energy&in&the&form&of&ATP;&results&in&the&splitting&of&water&and&the&release&of&oxygen)!
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1. Sunlight!strikes!the!chlorophyll!molecules!in!the!thylakoid!membrane;!the!energy!in!the!light!is!transferred!to!electrons.!
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These!highly!energized,!or!excited,!electrons!are!passed!from!chlorophyll!to!an!electron!
transport!chain!(series&of&proteins&embedded&in&a&membrane&along&which&energized&electrons&are&transported;&as&electrons&are&passed&from&molecule&to&molecule,&energy&is&released),!a!series!of!proteins!embedded!in!the!thylakoid!membrane.!
a. Each!protein!in!the!chain!passes!energized!electrons!along!from!protein!to!protein,!similar!to!a!bucket!brigade!in!which!a!line!of!people!pass!a!bucket!of!water!from!
person!to!person!to!fight!a!fire.!!At!each!step!along!the!transport!chain,!the!electron!
loses!energy,!just!as!some!of!the!water!might!be!spilled!from!buckets!in!the!fire'
fighting!chain.!
b. The!electron!transport!chain!allows!small!amounts!of!the!electron’s!energy!to!be!released!at!a!time.!!This!energy!is!used!to!form!ATP!from!ADP,!or!to!pump!from!ADP,!
or!to!pump!hydrogen!ions!into!the!center!of!the!thylakoid!disc.!
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After!the!electron!has!traveled!down!the!first!electron!transport!chain,!it!is!passed!down!a!
second!electron!transport!chain.!
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2. Following!the!second!electron!transport!chain,!the!electron!is!still!very!energized.!!So!that!this!energy!is!not!wasted,!the!electron!is!transferred!to!the!stroma!of!the!chloroplast.!!To!do!
this,!an!electron!carrier!molecule!called!NADP+!(nicotinamide!adenine!dinucleotide!
phosphate,!electron&carrier&molecule;&when&carrying&excited&electrons&it&becomes&NADPH)!is!used.!
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3. When!carrying!the!excited!electron,!NADP+!combines!with!a!hydrogen!ion,!H+,!and!becomes!NADPH.!!NADPH!will!play!an!important!role!in!the!formation!of!carbohydrates!later.!
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Restoring!Elections!To!Chlorophyll!
4. Although!some!of!the!light'energized!electrons!may!be!returned!to!chlorophyll!after!they’ve!moved!through!the!electron!transport!chain,!many!leave!with!NADPH!for!the!light'
independent!reactions.!!If!these!electrons!are!not!replaced,!the!chlorophyll!will!be!unable!to!
absorb!light!and!the!light'dependent!reactions!will!stop,!as!will!the!production!of!ATP.!
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To!replace!the!lost!electrons,!molecules!of!water!are!split.!
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5. Each!molecule!of!water!produces!one'half!molecule!of!oxygen!gas,!two!hydrogen!ions,!and!two!electrons.!!This!process!is!called!photolysis!(reaction&taking&place&in&the&thylakoid&membranes&of&a&chloroplast&during&lightBdependent&reactions&where&two&molecules&of&water&are&split&to&form&oxygen,&hydrogen&ions,&and&electrons).!!The!oxygen!of!photolysis!supplies!the!oxygen!we!breath.!
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PHOTOSYNTHESIS**B.***PHASE*2.*
Light'Independent!Reactions!(phase&of&photosynthesis&where&energy&from&lightBdependent&reactions&is&used&to&produce&glucose)!!
This!phase!of!photosynthesis!does!not!require!light.!
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It!takes!place!in!the!stroma!of!the!chloroplast.!
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6. The!Calvin!cycle!(series&of&reactions&during&the&lightBindependent&phase&of&photosynthesis&in&which&simple&sugars&are&formed&from&carbon&dioxide&using&ATP)!
a. We!begin!this!process!with!carbon!dioxide!reacting!with!ribulose!biphosphate!(RuBP)!to!produce!3'phosphoglyceric!acid!(PGA).!
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!!!©!!+!!©'©'©'©'©!!!!!©'©'©'©'©'©!!!!!©'©'©!!+!!©'©'©!&(CO2)&&&&&&&&&&&&(RuBP)&&&&&&&&&&&&&(unstable&intermediate)&&&&&&&(PGA)&&&&&&&&&&&&&(PGA)&
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b. PGA!molecules!are!converted!into!molecules!of!phosphoglyceraldehyde!(PGAL).!!This!requires!ATP!and!NADPH!from!the!light'dependent!reactions.!
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©'©'©!!+!!ATP!!+!!NADPH!!!!!©'©'©!!+!!(ADP!+!P)!!+!NADP+!!!(PGA)&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&(PGAL)&!
c. After!several!rounds!of!the!Calvin!cycle,!molecules!of!PGAL!leave!the!cycle!to!form!glucose!(C6H12O6).!
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©'©'©!!!!!©'©'©'©'©'©!&(PGAL)&&&&&&&&&&&&&&&&&&&&(Glucose)&!
Each!sugar!molecule!made!by!the!Calvin!cycle!contains!six!carbon!atoms,!and!because!
only!one!molecule!of!CO2!is!added!to!the!cycle!each!time,!it!takes!a!total!of!six!rounds!
of!the!cycle!to!form!one!sugar.!
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d. In!order!for!the!cycle!to!continue!incorporating!carbon!dioxide,!RuBP!must!be!generated.!!PGAL!molecules!are!used!to!form!RuBP.!!This!process!requires!ATP.!
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©B©B©&&!&&©B©B©B©B©&&&(PGAL)&&&&&&&&&&&&&&&&&&(RuBP)&!
e. Once!the!RuBP!is!formed,!it!is!available!to!unite!with!CO2!molecules!from!the!atmosphere!and!enter!another!turn!of!the!cycle.!
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