PowerLecture: Chapter 7 Where It Starts - Photosynthesis

 Plants are autotrophs, or self-nourishing organisms  The first autotrophs filled Earth’s atmosphere with oxygen, creating an ozone (O 3 ) layer  The ozone layer became a shield against deadly UV rays from the sun, allowing life to move out of the ocean Impacts, Issues: Sunlight and Survival

Fig. 7-1, p.106 Sunlight and Survival Apple orchard in Chelan, WA

Section 7.1

Photons  Packets of light energy  Each type of photon has fixed amount of energy  Photons having most energy travel as shortest wavelength (blue-violet light)‏

Visible Light  Wavelengths humans perceive as different colors  Violet (380 nm) to red (750 nm)  Longer wavelengths, lower energy

Pigments  Color you see is the wavelengths not absorbed  Light-catching part of molecule often has alternating single and double bonds  These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

Chlorophylls Wavelength absorption (%)‏ Wavelength (nanometers)‏ chlorophyll b chlorophyll a Main pigments in most photoautotrophs Pictured: Chlorophyll a

Accessory Pigments percent of wavelengths absorbed wavelengths (nanometers)‏ beta-carotene phycoerythrin (a phycobilin)‏ Carotenoids (pictured), Phycobilins, Anthocyanins

Fig. 7-3a, p.109 Pigments What is happening to the pigments in this photo?

Pigments in Photosynthesis  Bacteria Pigments in plasma membranes Pigments in plasma membranes  Plants Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

Section 7.2: T.E. Englemann’s Experiment Background  Certain bacterial cells will move toward places where oxygen concentration is high  Photosynthesis produces oxygen

T.E. Englemann’s Experiment

Fig. 7-4c, p.110 T.E. Englemann’s Experiment

Section 7.3: Photosynthesis Overview

Structure of a Chloroplast  Two outer membranes around semifluid interior (stroma) – bathes inner membrane  This single membrane is folded back on itself as a series of stacked, flattened disks  Each stack is called a thylakoid, which contains chlorophylls and other substances involved in photosynthesis

Photosynthesis Equation 12H 2 O + 6CO 2 6O 2 + C 2 H 12 O 6 + 6H 2 O WaterCarbon Dioxide OxygenGlucoseWater LIGHT ENERGY In-text figure Page 111

Leaf Cross Section

Stages of Photosynthesis

OVERVIEW:  Pigments absorb light energy, give up e -, which enter electron transfer chains  Water molecules split, ATP and NADH form, and oxygen is released  Pigments that gave up electrons get replacements Section 7.4: Light-Dependent Reactions

Photosystem Function: Harvester Pigments  Harvester pigments  When excited by light energy, these pigments transfer energy to adjacent pigment molecules  Each transfer involves energy loss

Pigments in a Photosystem

Photosystem Function: Reaction Center  This molecule (P700 or P680) is the reaction center of a photosystem  Reaction center accepts energy and donates electron to acceptor molecule Light-Harvesting Complex photon

Electron Transfer Chain  Adjacent to photosystem  Acceptor molecule donates electrons from reaction center  As electrons pass along chain, energy they release is used to produce ATP

NADPH NADP + + H + thylakoid compartment thylakoid membrane stroma ATP ADP + P i H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ PHOTOSYSTEM I sunlight PHOTOSYSTEM II LIGHT- HARVESTING COMPLEX Fig. 7-8, p.113 H+H+ e-e- e-e- e-e- e-e- e-e- e-e- H+H+ e-e- O2O2 H2OH2O cross-section through a disk-shaped fold in the thylakoid membrane

Section 7.5: Compare (P. 114)  Cyclic Pathway Noncyclic Pathway

Cyclic Electron Flow Cyclic Electron Flow  Electrons are donated by P700 in photosystem I to acceptor molecule are donated by P700 in photosystem I to acceptor molecule flow through electron transfer chain and back to P700 flow through electron transfer chain and back to P700  Electron flow drives ATP formation  No NADPH is formed

Cyclic Electron Flow

Noncyclic Electron Flow  Two-step pathway for light absorption and electron excitation  Uses two photosystems: type I and type II  Produces ATP and NADPH  Involves photolysis - splitting of water

Non-cyclic Electron Flow

Energy Changes Potential to transfer energy (volts)‏ H2OH2O 1/2O 2 + 2H + (Photosystem II)‏ (Photosystem I)‏ e–e– e–e– e–e– e–e– second transfer chain NADPH first transfer chain

How ATP is made: Chemosmotic Model:  Electrical and H + concentration gradients are created  H + flows down gradients into stroma through ATP synthetase  Flow of ions drives formation of ATP

OVERVIEW:  Synthesis part of photosynthesis  Take place in the stroma  Calvin-Benson cycle Section 7.6: Light-Independent Reactions

Calvin-Benson Cycle  Overall reactants Carbon dioxide Carbon dioxide ATP ATP NADPH NADPH Overall products GlucoseADP NADP + Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

Summary of Photosynthesis Figure 7-14 Page 120 light 6O 2 12H 2 O CALVIN- BENSON CYCLE C 6 H 12 O 6 (phosphorylated glucose)‏ NADPHNADP + ATP ADP + P i PGA PGAL RuBP P 6CO 2 end product (e.g., sucrose, starch, cellulose)‏ LIGHT-DEPENDENT REACTIONS 6H 2 O LIGHT-INDEPENDENT REACTIONS

Section 7.7: Alternative Pathways  C4 plants C3 plants

6 PGA + 6 glycolate 6 PGAL 1 PGAL Twelve turns of the cycle, not just six, to make one 6-carbon sugar RuBP Calvin-Benson Cycle CO 2 + water 5 PGAL Stomata closed: CO 2 can’t get in; O 2 can’t get out Rubisco fixes oxygen, not carbon, in mesophyll cells in leaf Fig. 7-11a3, p.117 C3 Plants

 In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA  Because the first intermediate has three carbons, the pathway is called the C3 pathway The C3 Pathway

Photorespiration in C3 Plants  On hot, dry days stomata close  Inside leaf Oxygen levels rise Oxygen levels rise Carbon dioxide levels drop Carbon dioxide levels drop  Rubisco attaches RuBP to oxygen instead of carbon dioxide  Only one PGAL forms instead of two

oxaloacetate malate C4 cycle pyruvate CO 2 12 PGAL 10 PGAL 2 PGAL 1 sugar RuBP Calvin- Benson Cycle Carbon fixed in the mesophyll cell, malate diffuses into adjacent bundle- sheath cell In bundle-sheath cell, malate gets converted to pyruvate with release of CO 2, which enters Calvin-Benson cycle 12 PGAL PEP Stomata closed: CO 2 can’t get in; O 2 can’t get out Fig. 7-11b3, p.117 C4 Plants

 Carbon dioxide is fixed twice In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate Oxaloacetate is transferred to bundle-sheath cells Oxaloacetate is transferred to bundle-sheath cells Carbon dioxide is released and fixed again in Calvin-Benson cycle Carbon dioxide is released and fixed again in Calvin-Benson cycle

 C3/C4 CAM

Stomata stay closed during day, open for CO 2 uptake at night only. C4 CYCLE Calvin- Benson Cycle C4 cycle operates at night when CO 2 from aerobic respiration fixed 1 sugar CO 2 that accumulated overnight used in C3 cycle during the day Fig. 7-11c3, p.117 CAM Plants

 Carbon is fixed twice (in same cells)‏  Night Carbon dioxide is fixed to form organic acids Carbon dioxide is fixed to form organic acids  Day Carbon dioxide is released and fixed in Calvin-Benson cycle Carbon dioxide is released and fixed in Calvin-Benson cycle

 Photoautotrophs Carbon source is carbon dioxide Carbon source is carbon dioxide Energy source is sunlight Energy source is sunlight  Heterotrophs Get carbon and energy by eating autotrophs or one another Get carbon and energy by eating autotrophs or one another Section 7.8: Carbon and Energy Sources

Linked Processes Photosynthesis  Energy-storing pathway  Releases oxygen  Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide

Fig. 7-12, p.118 sunlight energy Photosynthesis 1. H 2 O is split by light energy. Its oxygen diffuses away; its electrons, hydrogen enter transfer chains with roles in ATP formation. Coenzymes pick up the electrons and hydrogen 2. ATP energy drives the synthesis of glucose from hydrogen and electrons (delivered by coenzymes), plus carbon and oxygen (from carbon dioxide). glucose (stored energy, building blocks)‏ carbon dioxide, water oxygen Aerobic Respiration 1. Glucose is broken down completely to carbon dioxide and water. Coenzymes pick up the electrons, hydrogens. 2. The coenzymes give up the electrons and hydrogen atoms to oxygen-requiring transfer chains that have roles in forming many ATP molecules. ATP available to drive nearly all cellular tasks Carbon and Energy Sources

Photoautotrophs  Capture sunlight energy and use it to carry out photosynthesis Plants Plants Some bacteria Some bacteria Many protistans Many protistans

NORTH AMERICA ATLANTIC OCEAN AFRICA SPAIN Winter Spring Fig. 7-13, p.119 Photoautotrophs

Fig. 7-15, p.121 What is happening to this aquatic plant?

Fig. 7-16a, p.121 How might natural selection favor the evolution of different pigments at different depths in the seas? Red alga from a tropical reef

Fig. 7-16b, p.121 Coastal green alga (Codium)‏