8-3 The Reactions of Photosynthesis

Inside a chloroplast thylakoids: saclike membranes found in chloroplasts arranged in stacks known as grana contain photosystems that capture sunlight (light-dependent reactions) stroma: gel-like matrix surrounding the thylakoids region where the Calvin cycle takes place

NADPH electron carrier that can accept and transfer a pair of high-energy electrons to another molecule

Light Dependent Reactions reactions that occur in the thylakoids that produce O2 gas and convert ADP and NADP+ into energy carriers ATP and NADPH

B. Electron Transport Chain A. Photosystem 2 (II) light is absorbed by chlorophyll and energy transferred to electrons electrons transferred to electron transport chain water molecules broken up by enzymes into electrons, H+, and O2 B. Electron Transport Chain electrons move through electron transport chain to photosystem 1 (I) molecules in electron transport chain use energy to transport H+ from stroma into inner thylakoid

C. Photosystem 1 (I) pigments absorb energy which is passed to electrons electrons used to form NADPH from NADP+ D. Hydrogen Ion Movement inner thylakoid membrane fills up with H+ outside of membrane “+” charged and inside of membrane “-” charged

E. ATP Formation H+ pass through ATP synthetase to convert ADP to ATP

8-3 The Reactions of Photosynthesis (part 2)

The Calvin Cycle dark reactions occurring in the stroma that uses ATP and NADPH to produce high energy sugars

CO2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced Sugars and other compounds

CO2 Enters the Cycle 6 CO2 molecules are combined with six 5-carbon compounds to produce twelve 3-carbon compounds Energy Input energy from ATP and high-energy electrons from NADPH are used to convert the twelve 3-carbon compounds into higher energy forms

6-Carbon Sugars Produced two 3-carbon compounds are used to make a 6-carbon sugar 5-Carbon Molecules Regenerated the 10 remaining 3-carbon compounds are converted into six 5-carbon compounds which are used to fuel the next cycle

CO2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced Sugars and other compounds

Photosynthesis Review includes Light- dependent reactions Calvin cycle takes place in uses use take place in Thylakoid membranes Stroma NADPH ATP Energy from sunlight to produce of to produce ATP NADPH O2 Chloroplasts High-energy sugars

Factors Effecting the Rate of photosynthesis What a plant needs for maximum photosynthesis

water Plants need water for the light reaction Shortage slows photosynthesis Plants have adaptations that conserve water

CO2 and O2 Plants need high levels of carbon dioxide Plants need lower levels of oxygen If oxygen builds up in the leaf the plant undergoes photorespiration Plant may die Some plants store CO2 to prevent this

light As light increases so does photosynthesis But only to a point Plants can only absorb so much light…called saturation point The rate then levels off

Saturation point

temperature Photosynthesis takes place between 0 and 35 degrees Celsius The enzymes do not work below or above this range

Factors Affecting Photosynthesis water shortage slows or stops photosynthesis temperature photosynthesis depends on enzymes that function best between 0ºC and 35ºC light intensity increases photosynthesis until maximum rate reached for plant