Photosynthesis PDF

1 Photosynthesis Chapter 6: Energy for Life 2 Outline: Overview of Photosynthesis The Light Reactions—Harvesting Energy The Calvin Cycle Reactions—Making Sugars Variations in Photosynthesis Objectives: Describe the function of the chloroplast in photosynthesis. State the overall chemical equation fo...

1 Photosynthesis Chapter 6: Energy for Life 2 Outline: Overview of Photosynthesis The Light Reactions—Harvesting Energy The Calvin Cycle Reactions—Making Sugars Variations in Photosynthesis Objectives: Describe the function of the chloroplast in photosynthesis. State the overall chemical equation for photosynthesis. Recognize what is meant by the terms reduction and oxidation. Explain the low of electrons in the light reactions of photosynthesis. Explain how ATP and NADPH are generated in the light reactions. Describe how ATP and NADPH are utilized in the manufacture of carbohydrates by the Calvin cycle. 3 Overview of Photosynthesis · Plants are autotrophs (Producers of the biosphere) feed themselves and all of the consumers (most other living organisms on Earth) ~ feel Directly or indirectly, photosynthesis nourishes almost the entire living world:-D feed produces the sugars in plants that nourishes animals removing carbon dioxide and replaces it oxygen - - - - - Photosynthesis converts solar energy into chemical energy of carbohydrates - 4 Examples of Photosynthetic Organisms · Photosynthesis occurs inplants, algae, certain protists, and some -prokaryotes Estimation of 30% of world photosynthesis from protists - O -- 20% from photosynthetic prokaryotes O 50% from plants - /a 30 %20 ot So so protists prokaryotes plants protiet 20 So pro plats ku.ac.ae Leaves and Photosynthesis roofs · Leaves are the major locations of photosynthesis Stomate Their green color is from T chlorophyll, the green pigment within chloroplasts (carry on photosynthesis) s & wate, ffy) Leaf cross section Chloroplasts Vein - - Mesophyll -- Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf · O - - CO2 enters and O2 exits the leaf through microscopic pores called stomata · Roots absorb water. stored mesopt Stomata Chloroplast Outer membrane CO2 Mesophyll cell O2 5 6 Structures of Chloroplast The chlorophyll and other pigments are in the membranes of thylakoids (connected sacs in the chloroplast) Pigments absorb solar energy. Thylakoids may be stacked in columns called grana creating Thylakoid space Chloroplasts also contain stroma, a dense interior fluid surrounded by Double membrane. · A - Zooming in on the location of photosynthesis in a plant 7 Photosynthesis- evolution Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria (endosymbiont theory) The structural organization of these cells allows for the chemical reactions of photosynthesis 8 The Photosynthetic Process Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy ® C6H12O6 + 6 O2 + 6 H2O 6 28 + 2 1210 flight energy >+ SHE - H ,8 + 60 Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules (CH2O) and releasing oxygen as a byproduct 9 Photosynthesis: a redox process Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced Photosynthesis is an endergonic process; the energy boost is provided by light becomes reduced Gain of electrons 0000 Energy + 6 CO2 + 6 H2O C6 H12 O6 + 6 O2 becomes oxidized Loss of electrons Photosynthesis reverses the direction of electron flow compared to respiration 10 The Photosynthetic Process The are two stages of Photosynthesis the light reactions (the photo part) and Calvin cycle (the synthesis part) 11 The Photosynthetic Process: Light reactions The light reactions convert solar energy to the chemical energy of ATP and NADPH Occur in thylakoid membrane Chlorophyll absorbs solar energy and energizes electrons. Water is oxidized (splitted), releasing electrons, hydrogen ions, and oxygen. Reduce NADP+ to NADPH Generate ATP from ADP by photophosphorylation 12 The Photosynthetic Process: Calvin cycle reactions Occur in stroma The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH. 13 The Light Reactions—Harvesting Energy Light is a form of electromagnetic energy Solar energy can be described in terms of its wavelength and energy content. Visible light (used by photosynthetic organisms) contains various wavelengths. Shorter wavelengths contain more energy. Longer wavelengths contain less energy. Vision and photosynthesis are adapted to use the most prevalent wavelengths (visible light). Light also behaves as though it consists of discrete particles, called photons 14 Photosynthetic pigments: The light receptors Pigments are substances that absorb Light visible light Different pigments absorb different Reflected light Chloroplast wavelengths Wavelengths that are not absorbed are reflected or transmitted Leaves appear green because chlorophyll reflects and transmits green light Absorbed light Granum Transmitted light 15 Photosynthetic Pigments An absorption spectrum is a graph plotting a pigmentʼs light absorption versus wavelength Most photosynthesizing cells have chlorophylls and carotenoids. Both chlorophyll a and b absorb violet, blue, and red wavelengths better than other colors. Because green is reflected, leaves appear green. Accessory pigments, such as carotenoids, appear yellow or orange because they reflect those colors—they absorb light in the violet-blue-green range. Accessory pigments become noticeable in fall when chlorophyll breaks down. Suppose you were preparing to visit a space station that uses photosynthesis to provide you with oxygen. What color lightbulbs should you take with you? a) red b) green c) blue d) green and blue e) red and blue © 2021 Pearson Education, Ltd. 17 Leaf Colors 1 Leaves looks green because they reflect green light. Chlorophylls cover up accessory pigments, which are more visible in autumn. Carotenoids absorb violet, blue, green. But reflect yellow-orange When chlorophylls are no longer produced, we see the other pigments. 18 The Light Reactions: Capturing Solar Energy The light reactions convert solar energy to the chemical energy of ATP and NADPH (Nicotinamide adenine dinucleotide phosphate ) Electron pathway of the light reactions Capture sun’s energy and stores in the form of a hydrogen ion (H⁺) gradient Gradient used to produce ATP 19 20 The Light Reactions photosystems: PSI and PSII Photon Lightharvesting complexes Thylakoid membrane The reaction-center chlorophyll a of PS II is called P680 and of PS I is called P700 (wavelength) Photosystem Primary electron acceptor e- Consist of pigment complex (contains chlorophyll and carotenoids) and an electron acceptor Complex serves as antenna for gathering solar energy and passing it to the reaction center (chlorophyll a molecule). Reactioncenter complex STROMA Transfer of energy Pigment Special pair of molecules chlorophyll a molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) (a) How a photosystem harvests light Thylakoid membrane Named for order discovered (PSII work first) (b 21 The Light Reactions: Photosystem II (PSII) Absorption of solar energy energizes electrons. Electrons escape to electron acceptor molecule. Replacement electrons obtained by splitting water Releases oxygen gas as waste product Electrons are then sent through electron transport chain Series of carriers pass electrons along, releasing energy Energy stored in the form of H⁺ gradient will be used to make ATP 22 The Light Reactions: Photosystem I (PSI) Absorption of solar energy energizes electrons. Electrons captured by another electron acceptor molecule. Electrons and a hydrogen passed to NADP⁺ to become NADPH. Replacement electrons come from electron transport chain. 23 The Electron Transport Chain Organization of thylakoid membrane PS II, PS I, and the electron transport system are located within the thylakoid membrane. Promotes efficient transfer of electrons ATP synthase complex also in thylakoid membrane. ATP production Thylakoid space is a reservoir for H⁺ Each time water is split, 2 H⁺ remain in thylakoid space. Energy from electrons transferred between carriers used to pump more H⁺ from the stroma into the thylakoid space Establishes H⁺ gradient = large amount of potential energy 24 The Electron Transport Chain H⁺ gradient is used to produce ATP The H⁺ flow down concentration gradient Pass through ATP synthase complex Energy release allows for production of ATP Captures released energy NADP⁺ is a coenzyme that accepts electrons and a H⁺ to become NADPH. ku.ac.ae 25 26 27 The Calvin Cycle Reactions—Making Sugars Powered by ATP and NADPH generated by light reactions Occurs in stroma of chloroplasts End product is glucose C6H12O6. Three main steps Carbon dioxide fixation Carbon dioxide reduction Regeneration of first substrate (RuBP) 28 The Calvin Cycle:Three steps Fixation of carbon dioxide: CO2 from the atmosphere attached to RuBP by RuBP carboxylase (rubisco) 6-carbon molecule split into two 3-carbon molecules. Reduction of carbon dioxide: Uses NADPH (for electrons) and some ATP (for energy) from light reactions Forms G3P, which can become glucose Regeneration of RuBP: 1 G3P can be made into glucose or other organic molecules. 5 G3P used to reform RuBP (5-carbon molecule) Utilizes ATP from light reactions ku.ac.ae Phase 1: Carbon fixation Rubisco Calvin Cycle Phase 3: Regeneration of the CO2 acceptor (RuBP) Phase 2: Reduction 29 30 The Uses of G3P Plants and algae can make any molecule they need from G3P. Form amino acids, fatty acid, and glycerol Form glucose for energy needs Form sucrose for transport through plant Form starch for storage Form cellulose for cell walls 31 The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH 32 The Importance of Photosynthesis: A Review Life depends on photosynthesis The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits In addition to food production, photosynthesis produces the O2 in our atmosphere 33 The Importance of Photosynthesis: A Review The light reactions convert solar energy to the chemical energy of ATP and NADPH The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar Which incorrectly matches process and location? a) Oxygen gas is produced—the thylakoid space b) Activated chlorophyll donates an electron—the thylakoid membranes c) NADPH is oxidized to NADP+—the stroma d) ATP is produced—the intermembrane space e) Rubisco catalyzes carbon fixation—the stroma © 2021 Pearson Education, Ltd. Of these events from the light reactions, which occurs first? a) Light-induced reduction of the primary electron acceptor in the reaction center of PSII. b) While being split, electrons are taken out of water. c) Donation of electrons from reduced Pq to the cytochrome complex. d) Acceptance of electrons by Pc from the cytochrome complex. e) Pq gets electrons from the reduced primary electron acceptor of PS II. © 2021 Pearson Education, Ltd. If you were a cell that needed a large amount of ATP, what part of photosynthesis/the chloroplast would be most important? a) PSI b) outer membrane c) NADPH d) PEP carboxylase © 2021 Pearson Education, Ltd. Which is physically closest to the actual production of ATP in photosynthesis? a) thylakoid membrane b) outer membrane c) intermembrane space d) cytoplasm e) inner membrane © 2021 Pearson Education, Ltd. Suppose you were preparing to visit a space station that uses photosynthesis to provide you with oxygen. What color light bulbs should you take with you? a) red b) green c) blue d) green and blue e) red and blue © 2021 Pearson Education, Ltd. Which best links photosynthesis and cellular respiration? a) four carbon compounds b) chemiosmosis c) thylakoid membrane d) photosystems © 2021 Pearson Education, Ltd. Thank You ku.ac.ae