PhotosynthesisPhotosynthesisStage 2 - Conversion of light EnergyStage 2 - Conversion of light Energy

Stage 3 - Storage of EnergyStage 3 - Storage of Energy

Stage 2 - Conversion of Stage 2 - Conversion of Light EnergyLight Energy Light energy is converted to chemical Light energy is converted to chemical

energyenergy Excited electrons that leave the Excited electrons that leave the

chlorophyll pigments in Stage 1 are usedchlorophyll pigments in Stage 1 are used Excited electrons are passed through Excited electrons are passed through

proteins in the thylakoid membrane like a proteins in the thylakoid membrane like a ball being passed from person to personball being passed from person to person

Electron Transport ChainsElectron Transport Chains 1st ETC occurs between to pigment 1st ETC occurs between to pigment

moleculesmolecules Uses a protein that acts as a membrane Uses a protein that acts as a membrane

pumppump Electrons lose energy as they pass Electrons lose energy as they pass

through this proteinthrough this protein

Energy lost by these electrons is used in the Energy lost by these electrons is used in the protein to pump hydrogen ions (H+) into the protein to pump hydrogen ions (H+) into the thylakoid (active transport)thylakoid (active transport)

This pump along with splitting water This pump along with splitting water molecules provides a concentration molecules provides a concentration gradient inside the thylakoidgradient inside the thylakoid

Due to the high concentration gradient of Due to the high concentration gradient of H+ inside the thylakoid, some H+ diffuse H+ inside the thylakoid, some H+ diffuse out of the thylakoidout of the thylakoid

This passive transport occurs through This passive transport occurs through specialized carrier proteinsspecialized carrier proteins

These carrier proteins also work as an These carrier proteins also work as an enzymeenzyme

They also catalyze a reaction where a They also catalyze a reaction where a Phosphate is added to a molecule of ADPPhosphate is added to a molecule of ADP

ADP + P --> ATP (energy is produced)ADP + P --> ATP (energy is produced)

The ATP produced is used in the 3rd The ATP produced is used in the 3rd stage of photosynthesisstage of photosynthesis

2nd ETC occurs with pigment molecule2nd ETC occurs with pigment molecule Produces NADPH to help power 3rd stage Produces NADPH to help power 3rd stage

of photosynthesisof photosynthesis

Excited electrons combine with an Excited electrons combine with an electron acceptor NADP+electron acceptor NADP+

NADP+ + H+ --> NADPH (energy carrier)NADP+ + H+ --> NADPH (energy carrier)

Summary of Light Summary of Light Dependent ReactionsDependent Reactions

Pigment molecules in thylakoid absorb Pigment molecules in thylakoid absorb light energylight energy

Electrons excited by light move Electrons excited by light move through ETC in thylakoid through ETC in thylakoid

These electrons are replaced by water These electrons are replaced by water moleculesmolecules

Oxygen atoms from water combine Oxygen atoms from water combine to form oxygen gasto form oxygen gas

H+ concentration inside thylakoid H+ concentration inside thylakoid increasesincreases

Concentration gradient provides Concentration gradient provides energy to make ATPenergy to make ATP

H+ combine with NADP to create H+ combine with NADP to create NADPH, an energy carrier moleculeNADPH, an energy carrier molecule

Stage 3 - Storage of Stage 3 - Storage of EnergyEnergy Organic compounds are formed Organic compounds are formed

(glucose)(glucose) Light independent reactions Light independent reactions (dark rxns)(dark rxns) Transfer of carbon from CO2 to Transfer of carbon from CO2 to

organic compounds (carbon dioxide organic compounds (carbon dioxide fixation)fixation)

Calvin CycleCalvin Cycle Most common method of carbon Most common method of carbon

dioxide fixationdioxide fixation Occurs in 4 stepsOccurs in 4 steps Needs ATP and NADPH from Stage 2Needs ATP and NADPH from Stage 2

Step 1 - CO2 is added to a 5 carbon Step 1 - CO2 is added to a 5 carbon compoundcompound

Step 2 - Resulting 6C compound splits Step 2 - Resulting 6C compound splits into two 3C compounds. Phosphates into two 3C compounds. Phosphates from ATP and electrons from NADPH are from ATP and electrons from NADPH are added to form 3C sugarsadded to form 3C sugars

Step 3 - One 3C sugar is used to make Step 3 - One 3C sugar is used to make organic compounds (starch and sucrose)organic compounds (starch and sucrose)

These compounds are stored for later use These compounds are stored for later use by the organismby the organism

3D model of sucrose

Step 4 - the five other 3C sugars create Step 4 - the five other 3C sugars create the 5C sugars that start the cycle againthe 5C sugars that start the cycle again

The Calvin Cycle is named for Melvin CalvinThe Calvin Cycle is named for Melvin Calvin Discovered in 1950s at UC BerkleyDiscovered in 1950s at UC Berkley 3 CO2 molecules must enter the Calvin 3 CO2 molecules must enter the Calvin

Cycle to produce each 3C sugarCycle to produce each 3C sugar The 3C sugars are used to make other The 3C sugars are used to make other

organic molecules which provide energy for organic molecules which provide energy for growth and metabolismgrowth and metabolism

Factors that Affect Factors that Affect PhotosynthesisPhotosynthesis

Light - increased light intensity increases Light - increased light intensity increases until all pigments are being useduntil all pigments are being used

Carbon dioxide - at a certain Carbon dioxide - at a certain concentration photosynthesis can’t concentration photosynthesis can’t proceed any fasterproceed any faster

Temperature - unfavorable temp. can Temperature - unfavorable temp. can inactivate certain enzymesinactivate certain enzymes

Alternate Carbon Dioxide Alternate Carbon Dioxide FixationFixation

C4 PLANTS - Allows certain plants C4 PLANTS - Allows certain plants to fix CO2 into 4C compounds. to fix CO2 into 4C compounds. During the Hottest part of the day, During the Hottest part of the day, C4 plants have their stomata C4 plants have their stomata partially closed. Include corn, sugar partially closed. Include corn, sugar cane and crabgrass. Conserves cane and crabgrass. Conserves water in the plantwater in the plant

CAM PLANTS - Cactus, pineapples CAM PLANTS - Cactus, pineapples must survive in hot, dry climates. must survive in hot, dry climates. Plants open their Stomata at night Plants open their Stomata at night and close during the day. They and close during the day. They grow slowly, but lose less water.grow slowly, but lose less water.

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