Chapter 10 Photosynthesis BIOL 223 Photosynthesis Making food from light energy Photoautotrophs Use CO2 and water to make sugars Made life possible as we know it Provides carbohydrates for all higher levels of food chain produceon Liberates atmospheric oxygen O 2 waste product Carbon dioxide converted to sugar Process called carbon fixaeon Series of redox reaceons Water (hydrogen atoms) loses electrons Oxidized (OIL) Carbon dioxide gains electrons Reduced (RIG)
Summary equaeon for photosynthesis CO 2 + 2 H 2 O + photons (CH 2 O) n + H 2 O + O 2 carbon dioxide + water + light energy carbohydrate + oxygen + water Somewhat opposite of cellular respiraeon Photosynthesis CO 2 + 2 H 2 O + photons (CH 2 O) n + H 2 O + O 2 carbon dioxide + water + light energy carbohydrate + oxygen + water Cellular RespiraEon (CH 2 O) 6 C 6 H 12 O 6 + O 2 CO 2 + H 2 O + energy Energy trapped by photosynthesis approx 100 terawass 6x yearly global power consumpeon of human civilizaeon convert around 100,000,000,000 (billion) tons of carbon into biomass per year
Three Types of Photosynthesizers Domain: Eukaryota Kingdom: Plantae Domain: Eukaryota Domain: Prokaryota Kingdom: Protista Kingdom: Eubacteria The Components of Photosynthesis Chloroplasts Organelles in plants and algae, where photosynthesis takes place Light captured here Exist in great abundance in the mesophyll cells of plant leaves Double membrane bound like mitochondria Contain thylakoids Stacked as grana In the liquid filled stroma Photosynthesis Captured energy comes mostly from blue and red wavelengths of visible sunlight Absorbed by pigments in the thylakoids Chlorophyll a Accessory pigments Why plants look green high energy short wavelength gamma rays visible light x-rays low energy long wavelength ultraviolet infrared microwaves radiowaves
Site of Photosynthesis petiole blade epidermis mesophyll cells epidermis stomata nucleus chloroplast cell wall vacuole thylakoids stroma granum inner membrane outer membrane Energy from thylakoid sunlight is thylakoid membrane absorbed by thylakoid compartment pigments in the thylakoid membrane. 1. Leaf The primary site of photosynthesis in plants, leaves have a two-part structure: a petiole (or stalk) and a blade (normally thought of as the leaf). 2. Leaf cross section In cross section, leaves have a sandwichlike structure, with epidermal layers at top and bottom and mesophyll cells in between. Most photosynthesis is performed within mesophyll cells. Leaf epidermis is pocked with a large number of microscopic openings, called stomata, that allow carbon dioxide to pass in and water vapor to pass out. 3. Mesophyll cell A single mesophyll cell within a leaf contains all the component parts of plant cells in general, including the organelles called chloroplasts that are the actual sites of photosynthesis. 4. Chloroplast Each chloroplast has an outer membrane at its periphery; then an inner membrane; then a liquid material, called the stroma, that has immersed within it a network of membranes, the thylakoids. These thylakoids sometimes stack on one another to create... 5. A Granum Electrons used in photosynthesis will come from water contained in the thylakoid compartment, and all the steps of photosynthesis will take place either within the thylakoid membrane, or in the stroma that surrounds the thylakoids. Stages of Photosynthesis Two primary stages Light reaceons Strips electrons from water oxidaeon Boosts these electrons to higher energy levels Makes ATP and NADPH Calvin cycle Makes carbohydrates from high energy electrons and atmospheric CO 2 The Light ReacEons Electrons derived from water energeecally boosted by photons Electrons physically transferred passed along through a series of electron carriers NADP + NADPH carries them to second stage
Stages of Photosynthesis Two primary stages (conenued) Light reaceons Strips electrons from water Boosts these electrons to higher energy levels Calvin cycle Light independent reaceons Makes carbohydrates from high energy electrons and atmospheric CO 2 reduceon The Calvin Cycle Electrons carried by NADPH combined with carbon dioxide forms high energy sugar Glyceraldehyde 3 Phosphate (G3P) combined into complex carbohydrates powered by ATP from light reaceons Occurs in the stroma of the chloroplast First described by Melvin Calvin Photosynthesis works through two molecular complexes Photosystems II and I On thylakoid membranes composed partly of antennae chlorophyll and some accessory absorb and transmit solar energy Light ReacEons
Light ExcitaEon pigment absorbs light goes from a ground state to excited state which is unstable excited electrons fall back to the ground state photons are given off fluorescence e Excited state Energy of electron Photon Chlorophyll molecule Heat Photon (fluorescence) Ground state (a) Excitation of isolated chlorophyll molecule (b) Fluorescence Photosystem antennae A few hundred chlorophyll a and some accessory (pigments) s Photosystem Structure Carotene an orange pigment Xanthophyll a yellow pigment PhaeophyEn a[1] a graybrown pigment PhaeophyEn b[1] a yellowbrown pigment Chlorophyll a a blue green pigment Chlorophyll b a yellow green pigment transmit solar energy to reaceon centers ReacEon center Pair of modified chlorophyll a pheophyen Receive light energy transform it to chemical energy Photosystem Structure splits water and strips electrons off liberated hydrogen atoms also energizes stripped electrons Includes primary electron s Receive these high energy electrons Thylakoid membrane Photon Transfer of energy Light-harvesting complexes Photosystem e Special pair of chlorophyll a Reaction-center complex STROMA electron THYLAKOID SPACE (INTERIOR OF THYLAKOID)
1 Light e 2 P680 Photosystem II (PS II) Electron Flow two possible routes for electron flow cyclic and linear Linear electron flow primary pathway involves both photosystems produces ATP and NADPH using light energy photon hits pigment molecule energy passed among pigment unel it excites P680 excited electron from P680 transferred to the primary electron Linear Electron Flow (PS I) 2 H + + 1 / O 2 2 3 H 2 O e e e 2 P680 + (missing an electron) very strong oxidizing agent H 2 O is split by enzymes 1 Light P680 electrons transferred from hydrogen atoms to P680 + reducing it to P680 Photosystem II (PS II) O 2 is released Linear Electron Flow (PS II) Electrons passed down electron transport chain 2 H + + 1 / 2 O 2 e 2 H 2 O 3 e e Pq Electron transport chain 4 Cytochrome complex Pc from primary electron of PS II to PS I Energy released by fall 1 Light P680 5 ATP drives the creaeon of a proton gradient Photosystem II (PS II) Diffusion of H + into thylakoid space across membrane drives ATP synthase