Photosynthesis AP Biology PDF

AP Biology Unit 3 - “Cellular Energetics – Photosynthesis”  The History of Photosynthesis Jan van Helmont 1643 - plants gain most of their mass from water Joseph Priestley 1771 - plants release oxygen Jan Ingenhousz 1779 - plants...

AP Biology Unit 3 - “Cellular Energetics – Photosynthesis”  The History of Photosynthesis Jan van Helmont 1643 - plants gain most of their mass from water Joseph Priestley 1771 - plants release oxygen Jan Ingenhousz 1779 - plants need sunlight to produce oxygen Google celebrated his 287th birthda Frederick Frost (F. F.) Blackman 1905 - Photosynthesis consists of two reactions Cornelius B. Van Neil 1930 - Oxygen given off during photosynthesis comes from water.  Photosynthesis A complex chemical reaction that converts inorganic materials into organic materials. Performed by autotrophs (producers).  Photosynthesis Photosynthesis is a process by which plants and other autotrophs use the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy carbohydrates. 6 H2O + 6 CO2 + (light)→ 6 O2 + C6H12O6  OXIDATION - REDUCTION REACTION or REDOX REACTION Reduction – The addition of electrons to a substance involved in a reaction. Oxidation – The loss of electrons from a substance involved in a reaction.  Quick Review Questions What types of organisms perform photosynthesis? What type of reaction is photosynthesis? What is happening to the H2O in this reaction? What is happening to the CO2 in this reaction?  Raw Materials Photosynthesis takes place in the mesophyll tissues in leaves (and stems) of plants Chloroplast – organelle where photosynthesis occurs Stoma – exchanges CO2 & O2 between leaf and environment Roots absorb water Chloroplast Double membrane bound structure Stroma – fluid within chloroplast Thylakoid membranes – flattened sacs within stroma – Contain chlorophyll Grana – stacks of thylakoid membranes  Quick Review Questions Where does photosynthesis occur within a plant? What is the specific name of the plant tissue where photosynthesis occurs? What is contained within the thylakoid membranes? What are grana? What is the location of the stroma?  Pigments Pigments are light- absorbing molecules Dominant pigments - Chlorophyll a* & b (green) – Absorbs violet, blue and red light – Reflects green light Accessory pigments - Carotenoids (yellow and orange) – Absorbs violet- blue-green light  Photosystems Consists of pigment complexes and electron acceptors “Antenna” for gathering light Photosystem I – discovered first – P700 – Function is to produce ATP and NADPH Photosystem II – P680 – Function is to produce ATP  Quick Review Questions Which part of the electromagnetic spectrum can we see? What wavelength of light is absorbed by the plant? What wavelength of light is reflected by the plant? How is chlorophyll a different from chlorophyll b? What is the wavelength of light absorbed by photosystem 1?  Two Reactions of Photosynthesis Photosynthesis takes place in two reactions: 1) Light Reaction also referred to as: - Light Dependent Phase - Light Phase - Converts solar energy into ATP & NADPH 2) Calvin Cycle also referred to as: - Light Independent Reaction Phase / Dark Phase - Produces glucose using CO2 and energy Photosynthesis  NADP+ nicotinamide adenine dinucleotide phosphate NADP+ is a high energy carrying coenzyme used in anabolic reactions. NADP+ is reduced to become NADPH when it accepts 2 e- and a H+. NADP+ + 2 e- + H+ NADPH NADPH is used in the Calvin cycle.  The Light Reaction or The Light Dependent Reaction  Light Reaction Takes place in the thylakoid membranes Requires light Converts solar energy into chemical energy solar energy (photons) > ATP, NADPH Uses two photosystems Two electron pathways – Noncyclic – Cyclic  Light Reaction Sunlight is absorbed by chlorophyll and strikes H 2O Energizes electrons jump to the thylakoid membranes H2O is split into H and O O released as waste / H- replace lost e- / H+ form a concentration gradient Electrons move down the ETC Two electron pathways: – Noncyclic electron pathway Produces ATP and NADPH (energy-carrying compounds) – Cyclic electron pathway Produces ATP  Noncyclic Electron Pathway or Noncyclic Photophosphorylation Uses two photosystems – PSI & PSII Radiant / Solar energy is absorbed by PSI & PSII Starts with PSII – H2O is split into O2 and 2 H+ and 2 e- atoms – O2 released as waste product – H+ stay in thylakoid membrane forms H+ gradient H+ flow through ATP synthase and are used to create ATP ATP sent to Calvin cycle PSI – Electron acceptors pass their electrons to NADP+ – NADP+ and 2e- and H+ form NADPH (via NADP+ reductase) – NADPH sent to Calvin cycle  Cyclic Electron Pathway or Cyclic Photophosphorylation Starts with PSI Absorbs solar energy Electrons move down the ETC – Energy is captured and stored in the form of a H+ gradient – H+ flow down ATP synthase complexes which enables ADP + P to create ATP (phosphorylation) – Electrons return to PSI  Quick Review Questions Where does the light reaction occur in the chloroplast? What is converted into chemical energy? What happens to the H2O in the light reaction? What is created in the non-cyclic pathway? In the cyclic pathway? What is produced in this reaction that is used in the Calvin cycle?  The Calvin Cycle or The Dark Reaction or The Light Independent Cycle  Calvin Cycle Takes place in the stroma Light is not required Uses the ATP and NADPH from the light cycle to make glucose Three steps: – CO2 fixation – CO2 reduction – Regeneration of RuBP (ribulose biphosphate)  Carbon Dioxide Fixation First step: CO2 is attached to 3 RuBP (5-C molecule) Results in one 6-C molecule Splits into two 3- carbon molecules – 3 phosphoglycerate (3PG) for each CO2 *6 total molecules are formed  Carbon Dioxide Reduction Second Step: Uses ATP and NADPH from the Light Reaction CO2 reduced to sugar 2 - 3PG molecules (from Step 1) are reduced to G3P in two steps 6 molecules of G3P are formed 1 G3P exits cycle 5 G3P enter Step 3  Regeneration of RuBP Third Step (complex series of reactions): 5 molecules of G3P are needed to re-form 3 molecules of RuBP Uses 3 ATP from Light Reaction RuBP is now ready to receive CO2 again Cycle continues (total of 2 times) to make CH2O Each turn needs 9 ATP & 6 NADPH  G3P USES G3P can be converted to other organic molecules: – Glucose phosphate (glucose) Used by plants and animals for ATP Combined with fructose to form sucrose To make starch (for storage) and cellulose (cell walls) – Forms fatty acids and glycerol – Forms amino acids when N is added  Factors Affecting Photosynthesis Light intensity – increase in light increases photosynthesis – decrease in light decreases photosynthesis Temperature – 0°C - 35°C – higher or lower denatures enzymes Water availability – shortage slows or stops photosynthesis  Quick Review Questions Where does the Calvin Cycle occur in the chloroplast? What are the 3 major steps in the Calvin Cycle? What is the end result of step 1? What is the end result of step 2? What is the end result of step 3? What are the factors that affect photosynthesis? C3, C4, & CAM Photosynthesis  C3 Photosynthesis Occurs in most plants “C3” because the CO2 in first incorporated into a 3-C molecule (3PG) RuBP carboxylase, an enzyme, used to fix CO2 Photosynthesis takes place throughout the plant Calvin Cycle takes place in the mesophyll tissue Stomata are open during the day Results in G3P  C3 Plants Advantages: – more efficient under cool and moist conditions – takes place in normal light – requires fewer enzymes and – no specialized anatomy Disadvantage: – in hot, dry conditions photorespiration occurs  Photorespiration Occurs when CO2 levels are depleted As a result, O2 levels increase RuBP carboxylase fixes O2 instead of CO2 C4 Photosynthesis “C4” because CO2 is first incorporated into a 4-C (C4) molecule C4 (oxaloacetate) Photosynthesis takes place in inner cells (requires special anatomy - Kranz Anatomy) Calvin Cycle takes place in the bundle sheath tissue Stomata are open during the day Uses PEP Carboxylase, an enzyme, to fix CO2 Results in G3P  C4 Plants Plants are adapted to: – high light intensities – high temperatures – limited rainfall – photosynthesizes faster than C3 plants – less water lost by transpiration – sensitive to cold temperatures – no (or little) photorespiration occurs  CAM Photosynthesis Crassulacean-Acid Metabolism Plants are succulents Stomata open at night, closed during the day During the night – CAM plants fix CO2 and store it as an acid – Forms C4 (oxaloacetate) molecules – Stored in large vacuoles During the day – ATP and NADPH are available – Stomata closed for water conservation – C4 molecules release CO2 to Calvin cycle Results in G3P  CAM Plants Advantages: – better H2O efficiency than C3 plants – in extremely dry conditions, CO2 is used in respiration / O2 is used in photosynthesis – discovered in flowering and nonflowering plants, some ferns, and conifers  Quick Review Questions How are C3 and C4 plants different? How are C3 and C4 plants alike? How are C4 and CAM plants alike? How are C4 and CAM plants different? How are C3, C4, and CAM plants alike?