1. Complete the following chart (in “Do Now” on notes): OBJECTIVES: Describe the overall process of photosynthesis, including the inputs, outputs, and processes of the light reactions and the Calvin Cycle. TASK: 1. Complete the following chart (in “Do Now” on notes): Respiration Photosynthesis Carbon is (Redox) Location (in Eukaryotes) Energy is Types of organisms (‘trophs)
Photosynthesis Happens in Two Main Steps The light reactions of photosynthesis are responsible for capturing the energy of light, and storing it in chemicals like ATP. Water is split, producing O2. Those chemicals and CO2 from the atmosphere are then used by the Calvin Cycle to build sugars the plant needs to grow and survive.
Photosynthesis as a Process
The Carbon Cycle of Life C6H12O6 Photo-synthesis Respiration ATP Energy Produced CO2 Light Energy
Photosynthesis Happens in Chloroplasts Thylakoid Stroma
Chlorophyll is the green pigment that green plants use to capture light energy
Photosynthesis as a Process
P700 P680 Calvin Cycle
1: Chlorophyll in the chloroplast captures light energy Light strikes chlorophyll Electrons are knocked out of chlorophyll by light… they travel to step 2 Electrons are replaced when water is split Light electrons Chlorophyll 2 H+ + O H2O
2: Electrons are Transferred to Photosystem II The high-energy electrons taken from chlorophyll (or water, ultimately) are transferred to the electron transport chain of Photosystem II by an electron carrier protein called plastoquinone.
Step 3: The Electron Transport Chain of PSII Makes a Hydrogen Gradient Stroma H+ H+ H+ Inside Thylakoid (Lumen) H+ H+ Electrical energy allows ACTIVE transport from low concentration to high. H+ H+
3. H+ is at a high concentration in the thylakoids
Step 4: ATP is made by the enzyme ATP synthase Inside Thylakoid The energy to make ATP from ADP + P comes from the concentration gradient of hydrogen ions across the thylakoid membrane. ATPsynthase is a key enzyme that makes ATP Stroma
Step 5: Photosystem I The electrons are next transferred from the ETC of PS II to the reaction center of PS I. Yes, PS II happens BEFORE PS I, they were named in the order they were discovered. PS I is then oxidized by sunlight – the second time these electrons have been energized.
Steps 6-8: Electrons are transferred from the PSI reaction center to the ETC of PSI reaction center, and high energy electrons are ejected. Electrons travel through the ETC of PSI, generating a H+ gradient once again. The electrons from the ETC of PSI (along with H+) are transferred to NADP+ to form NADPH The electrons pass through a short ETC. The electrons are used to reduce NADP+ to NADPH.
Light Reaction Summary Light energy is captured by chlorophyll in the chloroplast. Light energy is stored in ATP and NADPH. The electrons used in the process come from the splitting of water. This is why plants make oxygen.
Do Now 12/23 OBJECTIVES: TASK: 1. Describe how the Calvin cycle builds carbohydrates. Define carbon fixation. TASK: If the Calvin cycle builds carbohydrates, what must it be doing with electrons?
The Calvin Cycle The Calvin Cycle builds sugars from CO2. (Carbon Fixation) The energy for the process comes from ATP and NADPH made during the light reaction. This process also happens in the chloroplast (specifically, the stroma).
Calvin Cycle… it’s complicated What you need to know FOR NOW: CO2 molecules are combined to make sugar (C6H12O6) Requires lots of ATP
Calvin Cycle = Carbon Fixation Carbon fixation is the process of turning inorganic carbon (like CO2) into organic carbon (like C6H12O6) Carbon fixation is the source of ALL CARBON BIOMASS ON EARTH. Thank you, autotrophs!
The Calvin Cycle is an Energy Hog To make 2 molecules of G3P required for a single glucose molecule, the cell must use 18 ATP molecules and 12 NADPH molecules. (NADPHNADP+ releases more energy than converting 7 ATPs to ADP!) Bottom line: it takes a lot of energy to turn CO2 and water into glucose! The process is about 75% efficient (plants will be able to recover 75% of the energy invested if they use aerobic respiration to break down the carbs they build)
How did Dr. Calvin figure this out, anyway? Melvin Calvin introduced radioactive carbon (14C) dioxide to photoautotrophs that were actively growing. He then killed them at various times and analyzed their chemical make up by autoradiological 2 dimensional chromatography. Thus, he could see which compounds were produced in what order. It took him about 10 years… and he won a Nobel Prize for his efforts in 1961
Calvin Cycle Recap The Calvin Cycle (aka “light-independent reactions”) BUILDS CARBOHYDRATE RuBisCo catalyzes carbon fixation Energy from ATP and NADPH (made in the light reactions) provide the energy to reduce carbon.
Photosynthesis Happens in Two Main Steps The light reactions of photosynthesis are responsible for capturing the energy of light, and storing it in chemicals like ATP. Water is split, producing O2. Those chemicals and CO2 from the atmosphere are then used by the Calvin Cycle to build sugars the plant needs to grow and survive.