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PHOTOSYNTHEIS Converting light energy into chemical energy stored in organic molecules carbon sun + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + sun C6H12O6 + 6O2 energy Regents Biology Energy Needs of Life Nutrition The process by which organisms get food and break it down so it can be used for metabolism Nutrients Substances that provide the energy and material needed for metabolic activity Organic: Proteins, carbohydrates, fats, vitamins Inorganic: minerals & water Regents Biology Energy Needs of Life All life needs a constant input of energy Heterotrophs (Animals) get their energy from “eating others” consumers eat food = other organisms = organic molecules make energy through respiration Autotrophs (Plants) produce their own energy (from “self”) producers convert energy of sunlight CO2 build organic molecules from H2O Photosynthesis: solar energy into chemical energy Regents Biology Photosynthesis Occurs in plants, algae, certain other protists, and some prokaryotes These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical globules) (c, d, e: LMs). (a) Plants (c) Unicellular protist 10 m (e) Pruple sulfur bacteria Figure 10.2 Regents Biology (b) Multicellular algae (d) Cyanobacteria 40 m 1.5 m Plant Structures Roots leaves Take in water and minerals from the soil Some roots store food Leaves Where photosynthesis takes place Absorbs CO2 & sunlight Usually flat stem/shoot Stem/Shoot Hold the leaves & allow them to receive sunlight Contains vascular tissue (bundles) Regents Biology roots Plant structure Obtaining raw materials sunlight leaves = solar collectors CO2 stomates = gas exchange H2O uptake from roots nutrients N, P, K, S, Mg, Fe… uptake from roots Regents Biology Function of Leaf Structures Cuticle cuticle waxy coating on epidermis reduces water loss protection Epidermis palisade mesophyll Protective tissue on outer layer Usually 1 cell thick Palisade mesophyll Upper epidermis lower epidermis high concentration of chloroplasts Photosynthesis Regents Biology Function of Leaf Structures Spongy mesophyll Large air spaces gas exchange CO2 in & O2 out Stomata Openings in the epidermis Allow for gas exchange Usually more on the lower epidermis Xylem Upper epidermis palisade mesophyll spongy mesophyll Guard Cells Kidney shaped cells surrounding the stomata Regulate the stomata Regents Biology cuticle lower epidermis Stomata Phloem Guard cells Plant Homeostasis Function of stomates CO2 in O2 out H2O out Function of guard cells open & close stomates close stomates when dehydrated guard cell stomate Regents Biology Transpiration Water evaporates from the stomates in the leaves pulls water up from roots Cohesion Adhesion Capillary Action Regents Biology Viewing the Leaf Epidermis Regents Biology Vascular/Conducting Tissues Xylem • carry water & minerals up from roots • supports the plant, holds it upright Regents Biology How does water move up from the roots? water molecules stick to other water molecules because opposite charges attract Regents Biology water molecules stick to molecules of another substance Phloem: food-conducting cells carry sugars (food) around the plant wherever they are needed new leaves fruit & seeds roots Regents Biology Viewing Vascular Tissue Xylem Regents Biology Phloem Phloem Xylem Chloroplast Structure Chlorophyll Pigment that absorbs light Chloroplast Double membrane containing chlorophyll Thylakoids Flattened membrane sacs Grana Stack of thylakoids Stroma Regions between grana Regents Biology absorb sunlight sun make ENERGY & SUGAR What is photosynthesis? ATP + Details: + Details: Details: Why is photosynthesis important? Regents Biology Details: PHOTOSYNTHESIS CO2 ENERGY building reactions collect sun energy use it to make ATP SUGAR building reactions take the ATP energy collect CO2 from air & H2O from ground use all to build sugars + H2O + water carbon dioxide Regents Biology sun ATP C6H12O6 Sugars + O2 + oxygen Photosynthesis Is a REDOX process Water is oxidized, carbon dioxide is reduced sun Consists of two processes ENERGY The light reaction The Calvin Cycle sugar Regents Biology building reactions SUGAR building reactions ATPused immediately to synthesize sugars Photosynthesis Light reactions (grana) light-dependent reactions Convert solar energy to chemical energy Split H2O, release O2, produce ATP, and form NADPH NADPH: electron carrier Calvin cycle (stroma) light-independent reactions sugar building reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 Regents Biology H2O CO2 Light NADP ADP + P CALVIN CYCLE LIGHT REACTIONS ATP NADPH Chloroplast O2 Regents Biology [CH2O] (sugar) Excitation of Chlorophyll by Light When a pigment absorbs light It goes from a ground state to an excited state, which is unstable e– Excited state Heat Photon (fluorescence) Photon Regents Biology Figure 10.11 A Chlorophyll molecule Ground state A photosystem Is composed of a reaction center surrounded by a number of light-harvesting complexes When a chlorophyll molecule absorbs energy one if its electrons gets bumped to a primary electron acceptor Thylakoid Photosystem Photon Thylakoid membrane Light-harvesting complexes Figure 10.12 STROMA Primary election acceptor e– Transfer of energy Regents Biology Reaction center Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Thylakoid membrane has two photosystems H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor 2 2 H+ + O2 H2O e 7 Fd Pq 8 e e– Cytochrome complex 3 NADP+ reductase NADPH 5 + H+ P700 e– P680 Light 6 ATP Regents Biology NADP+ + 2 H+ PC e– Light 1 Primary acceptor 4 Photosystem II (PS II) Photosystem-I (PS I) The organization of the thylakoid membrane Chemiosmosis: generates ATP by ATP synthase in the thylakoid membrane H2O CO2 LIGHT NADP+ ADP LIGHT REACTOR CALVIN CYCLE ATP NADPH STROMA (Low H+ concentration) O2 [CH2O] (sugar) Photosystem II Cytochrome complex Photosystem I NADP+ reductase Light 2 H+ 3 Fd NADPH Pq H2O THYLAKOID SPACE 1 (High H+ concentration) NADP+ + 2H+ + H+ Pc 2 1⁄ 2 O2 +2 H+ 2 H+ To Calvin cycle STROMA (Low H+ concentration) Thylakoid membrane ATP synthase ADP ATP P Regents Biology H+ Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH ATP Regents Biology The Calvin cycle in the stroma H2O Light CO2 Input 3 (Entering one CO2 at a time) NADP+ ADP LIGHT REACTION CALVIN CYCLE ATP Phase 1: Carbon fixation NADPH O2 Rubisco [CH2O] (sugar) 3 P 3 P P Short-lived intermediate P Ribulose bisphosphate (RuBP) P 6 3-Phosphoglycerate 6 ATP 6 ADP Calvin cycle uses more ATP than NADPH CALVIN CYCLE 3 ADP 3 ATP Phase 3: Regeneration of the CO2 acceptor (RuBP) Regents Biology P 6 NADPH 6 NADPH+ 6 P P 5 (G3P) 6 P Glyceraldehyde-3-phosphate (G3P) 1 Figure 10.18 6 P 1,3-Bisphoglycerate P G3P (a sugar) Output Glucose and other organic compounds Phase 2: Reduction Cyclic photophosphorylation If PS I can’t pass electron to NADP…it cycles back to PS II & makes more ATP, but no NADPH ATP Regents Biology A review of photosynthesis Light reaction Calvin cycle H2 O CO2 Light NADP+ ADP +P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP NADPH Chloroplast Figure 10.21 Regents Biology G3P Starch (storage) Amino acids Fatty acids O2 Light reactions: • Are carried out by molecules in the thylakoid membranes • Convert light eneragy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere Sucrose (export) Calvin cycle reactions: • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions Photosynthesis Overview Regents Biology A Look at Light Light is a form of electromagnetic energy that travels in waves Wavelength Distance between crests Determines the type of electromagnetic energy Regents Biology Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light (pigments) chlorophyll a absorbs best in red & blue wavelengths & least in green accessory pigments with different structures absorb light of different wavelengths chlorophyll b, carotenoids, xanthophylls Why are plants green? Regents Biology Action Spectrum of a Pigment Profiles the relative effectiveness of Rate of photosynthesis (measured by O2 release) different wavelengths of radiation driving photosynthesis (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids. Regents Biology Alternative Mechanisms of Carbon Fixation in Hot, Dry Climates Closed stomates conserve water, but… CO2 is depleted O2 builds up Rubisco binds to O2 instead of CO2 No ATP or glucose produced RuBP O 2 Regents Biology CO2 H2O O2 RuBisCo photorespiration corn C4 plants A better way to capture CO2 1st step before Calvin cycle, fix carbon with enzyme PEP carboxylase store as 4C compound 4C compound exported to bundle sheath cells where they release CO2 to be used in Calvin Cycle Regents Biology sugar cane CAM (Crassulacean Acid Metabolism) plants separate carbon fixation from Calvin cycle by TIME close stomates during day & open stomates during night at night: open stomates & fix carbon in 4C “storage” compounds in day: release CO2 from 4C acids to Calvin cycle increases concentration of CO2 in cells succulents, some cacti, pineapple Regents Biology It’s all in the timing! CAM plants cacti succulents Regents Biology pineapple C4 vs CAM Summary solves CO2 / O2 gas exchange vs. H2O loss challenge C4 plants separate 2 steps of C fixation anatomically in 2 different cells Regents Biology CAM plants separate 2 steps of C fixation temporally = 2 different times night vs. day How are they connected? Respiration glucose + oxygen carbon + water + energy dioxide C6H12O6 + 6O2 6CO2 + 6H2O + ATP Photosynthesis carbon sun + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + light C6H12O6 + 6O2 energy Regents Biology Energy cycle sun Photosynthesis plants CO2 glucose H2O sugars animals, plants Cellular Respiration ATP Regents Biology O2
