Module 2F - Photosynthesis Photosynthesis As we saw in the previous module, all In this module, we will examine cells can break down organic molecules photosynthesis a process for and use the energy that is released to manufacturing glucose from CO2 make ATP. and H2O usingggyg energy from light. In addition, some cells can manufacture During photosynthesis, light organic molecules from inorganic energy is captured and stored in substances using energy from light ((photosynthesisphotosynthesis)) or from inorganic the chemical bonds of glucose molecules. chemicals ((chemosynthesischemosynthesis).). 1 2 Objective # 36 Objective 36 Photosynthesis: 6CO + 6H O + light energy → Write a summary chemical 2 2 C H O + 6O equation for photosynthesis and 6 12 6 2 dibhiidffdescribe the origin and fate of DiDuring p hotosynt hiHihesis, H is remove d from H2O, leaving O2 as a waste each substance involved. product. The electrons in the removed H are energized by light, and then used to reduce CO2 to form glucose. 3 4 Objective # 37 Objective 37 All living organisms require organic molecules for survival. Organic Explain the role and importance molecules are used as an energy of photosynthesis for life on source, and as structural materials to earth, an d ident ify t he ma in build cell components. types of cells that carry out this Photosynthesis is the ultimate source process. of almost all organic molecules used by living organisms. It is also the main source of O in the atmosphere. 5 2 6 1 Objective 37 Objective 37 Organisms that can manufacture their Together, photosynthesis and aerobic own organic molecules from inorganic respiration form a complex cycle that substances are called autotrophs.autotrophs. is responsible for most of the energy Those that must consume organic flow through the biosphere. molecules are called heterotrophs..heterotrophs Photosynthesis uses CO2 + H2O to Autotrophs that use photosynthesis to produce glucose + O2. Aerobic manufacture organic molecules include respiration uses glucose + O2 to some monerans, some protists, and regenerate CO2 + H2O. almost all plants. 7 8 Photosynthesis Aerobic Respiration Objective # 38 Sunlight Heat Identify the 2 main stages of Electron Photo- Photo- O2 ATP system system Transport System photosynthesis and indicate II I H2O ADP+Pi + whhhere each stage ta klikes place in NADP + ADP+Pi ATP NADPH NAD NADH both prokaryotic and eukaryotic Calvin Cycle cells. CO2 Krebs ATP Cycle Glucose Pyruvate ADP+Pi 9 ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10 Objective 38 Objective 38 Photosynthesis occurs in 2 main stages: In eukaryotes, photosynthesis occurs inside chloroplasts.chloroplasts. Each chloroplast is surrounded by a double membrane. 1) The light-light-dependentdependent reactions, also called the energgpy capturing reactions Inside the inner membrane are flattened membranous sacs called thylakoids surrounded by a semisemi--fluidfluid 2) The carbon fixation reactions, also material called the stroma..stroma called the Calvin or C3 cycle The thylakoids are arranged in stacks called grana::grana 11 12 2 Structure of a Chloroplast In eukaryotes, the Sunlight lightlight--dependentdependent Plant Inner membrane cell Outer membrane reactions of photosynthesis take Chloroplast Photosystem place on the surface H2O O2 Thy la ko id Thylakoid of the thylakoid Membrane Light-Dependent Thylakoid Reactions membranes and the NADP+ NADPH ADP+Pi ATP carbon fixation Granum Stroma reactions (Calvin Calvin CO2 Organic Cycle molecules cycle) occur in the Stroma Copyright ©Copyright The McGraw-Hill © The McGraw-Hill Companies, Companies, Inc. Permission Inc. Permission required required for for reproduction reproduction oror display. 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. stroma. 14 Objective 38 The photosynthetic lamellae (membranes) of this bacterial cell are colored green: In prokaryotes, which lack chloroplasts: ¾ the lightlight--dependentdependent reactions of photosynthesis take place on the inner surface of the plasma membrane or on invaginations of the plasma membrane called photosynthetic lamellae..lamellae ¾ the carbon fixation reactions occur in the cytoplasm. 15 16 Objective # 39 Objective 39 Describe the lightlight--dependentdependent (energy capturing) During the light-light-dependentdependent reactions of photosynthesis with respect to: reactions (also called the energy a) how pigment molecules in the antenna complexes capturing reactionsreactions)) of are used to capture light energy photosynthesis, light energy is b) how the cappgytured energy is used for the captu re d by pigmen t mo lecu les an d production of ATP and NADPH during nonnon-- cyclic photophosphorylation transferred to electrons. The c) how the captured energy is used for the molecules used to carry out this production of ATP during cyclic process are organized into photophosphorylation photosystemsphotosystems.. 17 18 3 Each Photosystem consists of 2 parts: The Antenna Complex Antenna complex Also called lightlight--harvestingharvesting complex ¾Hundreds of accessory pigment Captures photons from sunlight and molecules channels them to the reaction center ¾Gather photons and feed the captured light energy to the reaction center chlorophylls Reaction center In chloroplasts, lightlight--harvestingharvesting ¾1 or more chlorophyll a molecules complexes consist of a web of ¾Passes excited electrons out of the chlorophyll molecules linked together photosystem and held tightly in the thylakoid 19 membrane by a matrix of proteins 20 A photosystem embedded in the thylakoid The Reaction Center membrane of a chloroplast: Transmembrane proteinprotein––pigmentpigment complex When a chlorophyll in the reaction center absorbs a photon of light, an electron is excited to a higher energy level Lihightt--energenergidlized electron can be trans ferre d to the primary electron acceptor, reducing it Oxidized chlorophyll then fills its electron “hole” by oxidizing a donor molecule 21 22 Objective 39 Release of an excited High energy electrons released by electron by the reaction center chlorophyll can the reaction follow one of 2 pathways: center ¾cyclic photophosphorylation chlorophyll (shown in ¾nonnon--cycliccyclic photophosphorylation green). 23 24 4 Objective 39 ¾ In cyclic photophosphorylation,photophosphorylation, the high energy electrons are used to make ATP by chemiosmosis. ¾ In nonnon--cycliccyclic pppphotophosphorylationhorylation,, first the high energy electrons are used to make ATP by chemiosmosis. Next, they are reenergized by light and used to reduce NADP+ to form NADPH. 25 26 Objective # 40 Describe the following events of the carbon fixation reactions (also called the Calvin or C3 cycle) of photosynthesis: a) carbon fixation b) thdihe reduction o fGAff PGA to form G3P (also called PGAL) c) the production of glucose from G3P d) the regeneration of RuBP from G3P 27 28 Objective 40 ¾ During the carbon fixation reactions (also called the Calvin or C3 cyclecycle)) of photosynthesis, energy from ATP and hdhydrogen from NADPH are use d to reduce CO2 in order to form glucose. 29 30 5.