PHOTOSYNTHESIS Energy For Life Unit

PHOTOSYNTHESIS Energy For Life Unit
Copyright © 2005 Pearson Prentice Hall, Inc.

Energy for Life Unit Capturing Solar Energy: Photosynthesis -
Releasing the energy in glucose Aerobic Respiration Producing Anaerobic respiration ATP The cycle Copyright © 2005 Pearson Prentice Hall, Inc.

THE CARBON OXYGEN CYCLE

(chloroplast) H2O CO2 ATP sugar O2 (mitochondrion) Figure :7-1 Title:
Interconnections between photosynthesis and cellular respiration Caption: Chloroplasts in green plants use the energy of sunlight to synthesize high-energy carbon compounds such as glucose from low-energy molecules of water and carbon dioxide. Plants themselves, and other organisms that eat plants or one another, extract energy from these organic molecules by cellular respiration, yielding water and carbon dioxide once again. This energy in turn drives all the reactions of life. (mitochondrion)

Internal Leaf Structure
cuticle Internal Leaf Structure upper epidermis Palisade Layer mesophyll cells Figure :7-2 part b Title: An overview of photosynthetic structures part b Internal leaf structure Caption: (b) A section of a leaf, showing mesophyll cells where chloroplasts are concentrated and the waterproof cuticle that coats the leaf's upper epidermis. stoma lower epidermis chloroplasts Spongy layer stomata vascular bundle (vein)

Chloroplast Structure
outer membrane inner membrane thylakoid stroma Figure :7-2 part c Title: An overview of photosynthetic structures part c Chloroplast in mesophyll cell Caption: (c) A single chloroplast, showing the stroma and thylakoids where photosynthesis occurs. channel interconnecting thylakoids granum (stack of thylakoids

Photosynthesis – A two part reaction
Light Reaction Solar energy stored as: A N Dark Reaction – Calvin Cycle ATP + NADPH + CO2 used to create Copyright © 2005 Pearson Prentice Hall, Inc.

Photosynthesis an Overview
(thylakoids) H2O O2 depleted carriers (ADP, NADP+) energized carriers (ATP, NADPH) Figure: 7-UN1 Title: Overview of Photosynthesis Caption: In light-dependent reactions, chlorophyll and other molecules embedded in the membranes of the thylakoids capture sunlight energy and convert some of it into the chemical energy stored in energy-carrier molecules (ATP and NADPH). Oxygen gas is released as a by-product. In light-independent reactions, enzymes in the stroma use the chemical energy of the carrier molecules to drive the synthesis of glucose or other organic molecules. (stroma) CO2 + H2O glucose

Light Reaction Requires Light
What is light? E r Narrow band Moderate energy level S wavelengths = higher energy Discrete units called p Copyright © 2005 Pearson Prentice Hall, Inc.

Wavelength (nanometers)
VIBGYOR Micro- waves Radio waves Gamma rays X-rays UV Infrared Visible light V I B G Y O R Figure :7-3 part a Title: Light, chloroplast pigments, and photosynthesis part a Visible light ("rainbow colors") Caption: (a) Visible light, a small part of the electromagnetic spectrum (top line), consists of wavelengths that correspond to the colors of the rainbow. 400 450 500 550 600 650 700 750 Wavelength (nanometers) ENERGY

Pigments Light c molecules C specific w of light Reflect others
Why is a blue shirt blue? Copyright © 2005 Pearson Prentice Hall, Inc.

Photosynthetic Pigments
Chlorophyll a – P p Chlorophyll b Carotenoids A P Anthocyanins Copyright © 2005 Pearson Prentice Hall, Inc.

Chlorophyll Borophyll
Acted upon by s e Excite e Electrons jump off molecule Hot e drive photosynthesis Copyright © 2005 Pearson Prentice Hall, Inc.

We saw this with the watch
The reverse can also happen. Solar energy can hit electron and raise it’s energy state. As electron falls back down to lower energy state plants can use the energy. Copyright © 2005 Pearson Prentice Hall, Inc.

light absorption (percent)
Absorbance of photosynthetic pigments 100 chlorophyll b 80 60 carotenoids light absorption (percent) chlorophyll a 40 Figure :7-3 part b Title: Light, chloroplast pigments, and photosynthesis part b Absorbance of photosynthetic pigments Caption: (b) Chlorophyll (blue and green curves) strongly absorbs violet, blue, and red light. Carotenoids (orange curve) absorb blue and green wavelengths. Question Based on the information in this graph, what color are carotenoids? What color is phycocyanin? 20 400 500 600 700 wavelength (nanometers)

Capturing Light Where Does This Occur ?
Stroma Membrane of Grana Copyright © 2005 Pearson CHLOROPLAST

The Light Reaction How it Works
Interior of Thylakoid

(High H+ concentration) H+ H+
Figure: E7-2 Title: Chemiosmosis: ATP Synthesis Caption: The thylakoid membrane does not allow hydrogen ions to leak out, except at specific protein channels that are coupled to ATP-synthesizing enzymes. When hydrogen ions flow through these channels, down their gradients of charge and concentration, the energy released drives the synthesis of ATP. (Low H+ concentration in stroma) H+ ADP ATP P

NADPH NADP+ photosystem II H+ H+ thylakoid membrane 2e– H+ H+
interior) Figure: E7-1 Title: Chemiosmosis: creating the hydrogen ion gradient Caption: The energy released from the exergonic reaction of these electron transfers in Photosystem II is used to power active transport of hydrogen ions across the thylakoid membrane from the stroma into the thylakoid interior. H+ H+ H+ H+ (stroma)

The Light Reaction Dark Reaction

electron transport chain
sunlight 2e– NADPH NADP+ + H+ 2e– electron transport chain energy level of electrons within thylakoid membrane 2e– Figure :7-4 Title: The light-dependent reactions of photosynthesis Caption: 1 Light is absorbed by photosystem II, and the energy is passed to electrons in the reaction-center chlorophyll molecules. 2 Energized electrons leave the reaction center. 3 The electrons move into the adjacent electron transport chain. 4 The chain passes the electrons along, and some of their energy is used to drive ATP synthesis by chemiosmosis. Energy-depleted electrons replace those lost by photosystem I. 5 Light strikes photosystem I, and the energy is passed to electrons in the reaction-center chlorophyll molecules. 6 Energized electrons leave the reaction center. 7 The electrons move into the electron transport chain. 8 The energetic electrons from photosystem I are captured in molecules of NADPH. 9 The electrons lost from the reaction center of photosystem II are replaced by electrons obtained from splitting water, a reaction that also releases oxygen, and H+ used to form NADPH. Question If these reactions produce ATP and NADPH, then why do plant cells need mitochondria? photosystem I energy to drive reaction center ATP synthesis 2e– photosystem II H2O 1/2 O2 + 2 H+

Light Reaction Overview
Photosystem II Generates A Photosystem I Generates N Splitting Water Generates Waste To Dark Reaction

The Dark Reaction How it Works
ATP + NADPH From Light Reaction CO2 - Fixation Unstable 6 Carbon Molecule 6 ATP 6 ADP 6 NADPH 6 NADP+ 3 ADP 3 ATP G3P 5 Carbon Molecule RuBP = Carbon Atom PGA 5 - G3P Copyright © 2005 Pearson Prentice Hall, Inc.

6 6 6 CO2 C 6 H2O 6 C C C C C 12 C C C RuBP PGA C3 cycle 12 ATP 12 ADP
Figure :7-6 Title: The C3 cycle of carbon fixation Caption: 1 Six molecules of RuBP react with 6 molecules of CO2 and 6 molecules of H2O to form 12 molecules of PGA. This reaction is carbon fixation, the capture of carbon from CO2 into organic molecules. 2 The energy of 12 ATPs and the electrons and hydrogens of 12 NADPHs are used to convert the 12 PGA molecules to 12 G3Ps. 3 Two G3P molecules are available to synthesize glucose or other organic molecules. This occurs outside the chloroplast and is not part of the C3 cycle. 4 Energy from 6 ATPs is used to rearrange 10 G3Ps into 6 RuBPs, completing one turn of the C3 cycle. 6 ADP 12 NADPH 12 C C C 6 ATP 12 NADP+ G3P C C C C C C glucose (or other organic compounds)

THE CALVIN CYCLE

What do plants do with G3P
G3P = glyceraldehyde 3 phosphate Phosphoglyceraldehyde Link 2 G3P to form Glucose S Glucose C Other Organic Molecules C R Copyright © 2005 Pearson Prentice Hall, Inc.

Dark Reaction Overview
ATP + NADPH Energy Used CO2 Bonded to 5 C Ribulose Biphosphate G3P Produce  G Low Energy ADP + NADP+ Returned to Light Reaction Copyright © 2005 Pearson Prentice Hall, Inc.

Photosynthesis Overview
Calvin Cycle 6X

Photosynthesis Tally WS
Reaction Energy Source Reactants Products Site of Reaction Light Reaction Calvin Cycle

Problems Faced By Plants
Desiccation – D Specialized Structures Stop Water Loss C S Photorespiration – oxygen O2 attaching to R instead of CO2 Slows photosynthesis Some Plants have special CO2 capturing molecule phosphoenol pyruvate C3 Copyright © 2005 Pearson Prentice Hall, Inc.

Normal Plants – C3 – No special structures to stop photorespiration
within chloroplast in mesophyll cell C3 plants use the C3 pathway CO2 O2 PGA CO2 C3 CYCLE RuBP G3P glucose bundle- sheath cells Figure :7-8 part a Title: Comparison of C3 and C4 plants part a C3 plants use the C3 pathway Caption: (a) In C3 plants, only the mesophyll cells carry out photosynthesis. All carbon fixation occurs by the C3 pathway. With low CO2 and high O2 levels, photorespiration dominates in C3 plants, because the enzyme that should catalyze the RuBP plus CO2 reaction catalyzes the RuBP plus O2 reaction instead. Normal Plants – C3 – No special structures to stop photorespiration

C4 Plants- Special CO2 Capturing Molecule
C4 plants use the C4 pathway within chloroplast in mesophyll cell CO2 PEP 4-carbon molecule AMP C4 Pathway ATP pyruvate CO2 O2 bundle- sheath cells PGA CO2 C4 Plants- Special CO2 Capturing Molecule Figure :7-8 part b Title: Comparison of C3 and C4 plants part b C4 plants use the C4 pathway Caption: (b) In C4 plants, both the mesophyll cells and bundle sheath cells contain chloroplasts and participate in photosynthesis. CO2 is combined with PEP by a more selective enzyme, and the carbon is shuttled into bundle sheath cells by a four-carbon molecule, which releases CO2 into the bundle sheath cells. Higher CO2 levels allow efficient carbon fixation (with little photorespiration) in the C3 pathway of the bundle sheath cells. Notice that the regeneration of PEP requires energy from ATP. Question Why do C3 plants have an advantage over C4 plants under conditions that are not hot and dry? C3 CYCLE RuBP G3P glucose within chloroplast in bundle-sheath cell

C3 plants use the C3 pathway within chloroplast in mesophyll cell
CO2 O2 PGA CO2 C3 CYCLE RuBP G3P glucose bundle- sheath cells C4 plants use the C4 pathway within chloroplast in mesophyll cell CO2 PEP 4-carbon molecule AMP C4 Pathway ATP Figure :7-8 Title: Comparison of C3 and C4 plants Caption: (a) In C3 plants, only the mesophyll cells carry out photosynthesis. All carbon fixation occurs by the C3 pathway. With low CO2 and high O2 levels, photorespiration dominates in C3 plants, because the enzyme that should catalyze the RuBP plus CO2 reaction catalyzes the RuBP plus O2 reaction instead. (b) In C4 plants, both the mesophyll cells and bundle sheath cells contain chloroplasts and participate in photosynthesis. CO2 is combined with PEP by a more selective enzyme, and the carbon is shuttled into bundle sheath cells by a four-carbon molecule, which releases CO2 into the bundle sheath cells. Higher CO2 levels allow efficient carbon fixation (with little photorespiration) in the C3 pathway of the bundle sheath cells. Notice that the regeneration of PEP requires energy from ATP. Question Why do C3 plants have an advantage over C4 plants under conditions that are not hot and dry? pyruvate CO2 O2 bundle- sheath cells PGA CO2 C3 CYCLE RuBP G3P glucose within chloroplast in bundle-sheath cell

Carbon Oxygen Cycle Glucose + O2 A T P CO2 + H2O

heat radiated into space sun outer space
CO2 CFCs methane nitrous oxide sunlight atmosphere heat trapped in atmosphere volcano forest fires factories Figure: 41-15 Title: Increases in greenhouse gas emissions contribute to global warming Caption: Incoming sunlight warms Earth's surface and is radiated back to the atmosphere. Greenhouse gases absorb some of this heat, trapping it in the atmosphere. Human activities have greatly increased levels of greenhouse gases, resulting in a gradual rise in average global temperatures. Why do temperatures rise in an actual greenhouse? Why is this a good analogy for heat-trapping by greenhouse gases? vehicle emissions houses cows Copyright © 2005 Pearson Prentice Hall, Inc.

Global Warming What Is It ?
The rising of Earths average temperature Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in (UNIPCC 2007) Thought to be anthropogenic Intergovernmental Panel on Climate Change (IPCC) 2007 “Very Likely” 95% probability (UNIPCC 2007) Increase in CO2 is primary concern CO2 Levels have increased 36% since mid 1700’s highest level in 650,000 years Recent Climate Change - Atmosphere Changes, Science, Climate Change, U.S. EPA" . United States Environmental Protection Agency‎ (2007). Copyright © 2005 Pearson Prentice Hall, Inc.

CO2 concentration (parts per million by volume)
average world temperature (ºC) CO2 temperature Figure: 41-16 Title: Global warming parallels CO2 increases Caption: The CO2 concentration of the atmosphere (blue line) has increased steadily since The dashed portion of that curve represents measurements made from air trapped in ice cores; the solid portion reflects direct measurements made at Mauna Loa, Hawaii. Average global temperatures (red line) have also increased gradually, paralleling the increasing atmospheric CO2. (With thanks to Drs. Kevin Trenberth and Jim Hurrell of the National Center for Atmospheric Research.) Copyright © 2005 Pearson Prentice Hall, Inc.

burning of fossil fuels
reservoir processes/locations CO2 in atmosphere trophic levels burning of fossil fuels fire Respiration CO2 dissolved in ocean Figure: 41-8 Title: The carbon cycle Caption: Carbon is stored in the atmosphere, in limestone, in the oceans, and in fossil fuels. Carbon dioxide is captured from the atmosphere during photosynthesis and passed up through the trophic levels. It is released during respiration from all trophic levels and by the burning of forests and fossil fuels. producers consumers wastes, dead bodies fossil fuels limestone soil bacteria and detritus feeders Copyright © 2005 Pearson Prentice Hall, Inc.

energy from sunlight O2 CO2 H2O ATP NADPH Light Reaction Dark Reaction
Figure :7-7 Title: A summary diagram of photosynthesis Caption: The light-dependent reactions in the thylakoids convert the energy of sunlight into the chemical energy of ATP and NADPH. Part of the sunlight energy is also used to split H2O, forming O2. In the stroma, the light-independent reactions use the energy of ATP and NADPH to convert CO2 and H2O to glucose. The depleted carriers, ADP and NADP+, return to the thylakoids to be recharged by the light-dependent reactions. Question Could a plant survive in an oxygen-free atmosphere? Dark Reaction ADP NADP+ H20 chloroplast glucose

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