Stage 2 - Conversion of light Energy Stage 3 - Storage of Energy Photosynthesis Stage 2 - Conversion of light Energy Stage 3 - Storage of Energy

Stage 2 - Conversion of Light Energy Light energy is converted to chemical energy Excited electrons that leave the chlorophyll pigments in Stage 1 are used Excited electrons are passed through proteins in the thylakoid membrane like a ball being passed from person to person

Electron Transport Chains 1st ETC occurs between to pigment molecules Uses a protein that acts as a membrane pump Electrons lose energy as they pass through this protein

Energy lost by these electrons is used in the protein to pump hydrogen ions (H+) into the thylakoid (active transport) This pump along with splitting water molecules provides a concentration gradient inside the thylakoid

Due to the high concentration gradient of H+ inside the thylakoid, some H+ diffuse out of the thylakoid This passive transport occurs through specialized carrier proteins

These carrier proteins also work as an enzyme They also catalyze a reaction where a Phosphate is added to a molecule of ADP ADP + P --> ATP (energy is produced)

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

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

Excited electrons combine with an electron acceptor NADP+ NADP+ + H+ --> NADPH (energy carrier)

Summary of Light Dependent Reactions Pigment molecules in thylakoid absorb light energy Electrons excited by light move through ETC in thylakoid These electrons are replaced by water molecules

Oxygen atoms from water combine to form oxygen gas H+ concentration inside thylakoid increases

Concentration gradient provides energy to make ATP H+ combine with NADP to create NADPH, an energy carrier molecule

Stage 3 - Storage of Energy Organic compounds are formed (glucose) Light independent reactions (dark rxns) Transfer of carbon from CO2 to organic compounds (carbon dioxide fixation)

Calvin Cycle Most common method of carbon dioxide fixation Occurs in 4 steps Needs ATP and NADPH from Stage 2

Step 1 - CO2 is added to a 5 carbon compound Step 2 - Resulting 6C compound splits into two 3C compounds. Phosphates from ATP and electrons from NADPH are added to form 3C sugars

These compounds are stored for later use by the organism Step 3 - One 3C sugar is used to make organic compounds (starch and sucrose) These compounds are stored for later use by the organism 3D model of sucrose

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

The Calvin Cycle is named for Melvin Calvin Discovered in 1950s at UC Berkley 3 CO2 molecules must enter the Calvin Cycle to produce each 3C sugar The 3C sugars are used to make other organic molecules which provide energy for growth and metabolism

Factors that Affect Photosynthesis Light - increased light intensity increases until all pigments are being used Carbon dioxide - at a certain concentration photosynthesis can’t proceed any faster Temperature - unfavorable temp. can inactivate certain enzymes

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

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

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