Photosynthesis Chapter 05 Textbook PDF

Because learning changes everything. ® Chapter 05 Photosynthesis...

Because learning changes everything. ® Chapter 05 Photosynthesis Presented by: Amini, MPH, MT, LE Rodrigo A. Torres/Glowimages/Superstock © 2022 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.  Key concepts Overview of Photosynthesis Reactions That Harness Light Energy Molecular Features of Photosystems Synthesizing Carbohydrates via the Calvin Cycle Variations in Photosynthesis © McGraw Hill, LLC 2  Life depends on photosynthesis Biologist consider photosynthesis to be the most important metabolic process on Earth Photosynthesis is the process of converting sun light (kinetic) energy into chemical (Covalent bond, potential, stored) energy. Photosynthetic organisms are producers ( Autotrophs) - the basis of every ecosystem on Earth. photo means light and synthesis is storing that energy by covalently bonding atoms together and forming carbohydrates, fats, and protein. Heterotrophs are consumers (animal and fungi), and other consumers eat the producers. Photo-synthesizers in our planet are Algae, plants, protist and some bacteria zhang bo/E+/Getty Images Section 5.1 © McGraw Hill, LLC 3  Photosynthesis - Sunlight powers photosynthesis process Oxygen is a by-product of photosynthesis Photosynthesis is an Oxidation- Reduction (redox) process -Photosynthetic organisms need just a few simple ingredients to make their own molecules of sugar: Sunlight Carbon dioxide (CO2) Water -As sugar is formed during photosynthesis, oxygen gas is released into the air. Being able to carry out photosynthesis is evolutionarily advantageous for organisms because it allows them to produce oxygen. make their own food. make food for heterotrophs. use carbon dioxide. Mitochondria Mesophyll Cell Section 5.1 Figure 5.1 © McGraw Hill, LLC 4  Clicker question #1 The process of photosynthesis is evolutionarily advantageous for organisms because it allows them to: A. produce oxygen. B. make their own food. C. make food for heterotrophs. D. use carbon dioxide. E. All of the choices are correct. © McGraw Hill, LLC Sunlight as energy source Photons are packets of light kinetic energy; The sunlight emits energy in waves Visible light is only one part of the sun’s energy. Photon’s wavelength is the distance it moves during a complete vibration; it is measured by nanometers. The shorter a photon’s wavelength, the more energy it contains, the more damaging to DNA. The portion of the spectrum that reaches earth’s surface is between 400 to 750 nanometers The main components of sunlight are Gamma rays, X-rays and Ultraviolet radiation = damage DNA Only about 1% of sun energy is used for photosynthesis O Electromagnetic z spectrum Is the range of all o possible frequencies of n radiation e L a Melanin Microwaves y White color- absent of color e Black color – all the color r present © McGraw Hill, LLC Section 5.2 Figure 5.2 6  Light Energy capturing pigment molecules: Chlorophyll a, b, and carotenoids Chlorophyll a is the main photosynthetic pigment in plants, algae and cyanobacteria Pigments found in plants “specialize” in absorbing energy from different wavelengths of light. Only absorbed light is useful for photosynthesis. What we see with our eyes is the reflected light which is not absorbed by plant’s chlorophyll Plant pigments do not absorb green light Green light is reflected, Carotenoids reflect longer wavelengths of light, so they appear red, orange or yellow Accessory pigments are always present in plants, but they are masked by Chlorophyll Chlorophyll a – Most abundant, a green photosynthetic pigment in plants, alga, and Reflected cyanobacteria Chlorophyll b & Carotenoids = are accessory pigments; energy-capturing pigment molecules Anthocyanins – Protect leaves from damage by UV radiation Section 5.2 Figure 5.3 © McGraw Hill, LLC 7  TABLE 5.1 Pigments of Photosynthesis Pigment Color(s) Organisms Major Pigment Chlorophyll a Blue-green Plants, algae, cyanobacteria Accessory Pigments Chlorophyll b Yellow-green Plants, green algae Carotenoids Red, orange, yellow Plants, algae, (carotenes and bacteria xanthophylls) Section 5.2 Table 5.1 © McGraw Hill, LLC 8  5.1 Mastering concepts Why is photosynthesis essential to both autotrophs and heterotrophs? © McGraw Hill, LLC  Clicker question #2 Why are leaves green? A. Heterotrophs see green better than any other color. B. Plant pigments absorb green light. C. Plant pigments absorb almost every wavelength except for green. D. Plant pigments change yellow light that they absorb to green light that we see. © McGraw Hill, LLC 10  Chloroplasts are the sites of photosynthesis Chloroplast – contains Chlorophyll = light-harvesting pigments, embedded in the thylakoid membrane. Mesophyll (middle, leaf) C3 pathway cells contain multiple chloroplasts; photosynthesis takes place in Mesophyll cells. Gas exchange occurs at leaf pores called stomata (s. Stoma – mouth) One Stack of Thylakoid is called granum (p. Grana) Thylakoids increase the surface Chlorophyll in the area where light energy gets picked thylakoid membranes up. capture sunlight Stroma – Fluid part within the double membrane of chloroplast. Sugars are made in this part of chloroplasts Section 5.3 Figure 5.4 © McGraw Hill, LLC 11  Photosynthesis occurs in 2 phases 1. Light Reaction 2. Calvin Cycle (Carbon reaction) Photosynthesis occurs in photosystems A photosystem is a large complex protein in the thylakoid membrane. This complex protein contains a pigment molecule in chloroplasts called Chlorophyll that absorbs light and generates O2 during the light reactions of photosynthesis A photosystem consists of: 1) antenna pigments 2) A reaction center that contains chlorophyll Electron comes from splitting the H2O Section 5.3 molecule Figure 5.5 © McGraw Hill, LLC 12  Clicker question #3 Of the following list of plant structures, which is the second smallest? A. chloroplast B. granum C. mesophyll cell D. chlorophyll E. thylakoid © McGraw Hill, LLC 13  5.2 Mastering concepts Describe the relationship among the chloroplast, stroma, grana, and thylakoids. © McGraw Hill, LLC 14  Photosynthesis occurs in two stages 1. LIGHT REACTIONS: The light reactions begin photosynthesis. The light reactions occur in the thylakoid membrane Water + Light energy is captured by pigment molecules and converted to chemical energy (ATP/NADPH) ADP and NADP are electron carrier molecules ATP and NADPH are produced to carry stored energy. 2. CARBON REACTIONS (Calvin Cycle): ATP and NADPH produced during light reactions carry Oxygen gas (O2) is formed as a the stored chemical energy derived from sunlight. byproduct ATP and NADPH power the carbon reactions. Energy (ATP/NADPH) is used to produce sugar. In the carbon reaction, the energy from ATP/NADPH is used to break up molecules of CO2 and build molecules of sugar. Section 5.4 © McGraw Hill, LLC Figure 5.6 15  How do the light reactions work? Ions flow down the concentration gradient into the Thylakoid space by Active transport NADP+ – is an Electron carrier H2O gets in through osmosis Water is the initial electron donor Herbicides stop light Rxn O2 Roundup/Gl Escape through yphosate – simple inhibits an diffusion enzyme/aa ATP Synthase – moves H+ out into Stroma by Facilitated diffusion synthesis and makes ATP. Movement is kinetic energy. this kinetic energy is used to Covalently bond ADP to P to make ATP. This Process is called Chemiosmotic phosphorylation –> makes ATP © McGraw Hill, LLC 16  PSII produces ATP Electrons from PSII move down an electron transport chain. H+ is pumped into the thylakoid H+ leaves through ATP synthase. ATP synthetase produces ATP through chemiosmotic phosphorylation. Section Figure 5.4 Access the text alternative for these images 5.9 © McGraw Hill, LLC 17  PSI produces NADPH Electrons arrive at the second photosystem (PSI). When light hits PSI, chlorophyll transfers light energy to the electrons. Electrons move to a second electron transport chain. Electrons reduce NADP+ to NADPH. Section Figure 5.4 Access the text alternative for these images 5.9 © McGraw Hill, LLC 18  Some weed killers block the light reactions Some chemicals, such as the weed killers DCMU and paraquat, block the light reactions by interfering with the flow of electrons. image100/Corbis/Getty Images © McGraw Hill, LLC Section 5.4 Figure 5.A 19  Clicker question #4 How do the light reactions produce ATP? (Select the one best answer.) A. Potential energy stored in a hydrogen ion gradient is used to synthesize ATP. B. Photosystem I directly adds a phosphate to ADP. C. Photosystem II directly adds a phosphate to ADP. D. Energy released by electrons is directly used to synthesize ATP. © McGraw Hill, LLC 20  Carbon reactions (Calvin Cycle, C3 pathway) produce primarily glucose (as well as starch, cellulose, and sucrose) The carbon reactions occur in stroma. ATP and NADPH from the light reaction power the Calvin cycle, which assembles CO2 molecules into sugars, glycerol, triglyceride, and amino acids. Section 5.6 Access the text alternative for slide images. Figure 5.9 © McGraw Hill, LLC 21  5.4 Mastering concepts Use the following terms to create a concept map showing how the light reactions work: NADPH Pigment Water Energy Electrons PSI Chlorophyll ATP Light PSII Electron transport chain Oxygen © McGraw Hill, LLC 22  Calvin Cycle = Carbon reactions require Rubisco Enzyme C3 pathway - The first reaction in the Calvin Carbon Rxn takes cycle is catalyzed by an enzyme place in Stroma called Rubisco, which makes carbon fixation possible. Calvin’s cycle has 3 steps: 1. Carbon Fixation - chloroplast absorbs CO2 takes it from a gas state and chemically bonds it onto ATP and a molecule of RuBP. An unstable NADPH from six-carbon organic molecule is Light reaction give their P produced and é energy 2. PGAL synthesis - Small to PGA and organic molecules are formed. make PGAL ATP and NADPH from light reactions are cashed in. Their The energy of energy is used when PGA is activation is used converted to PGAL. PGAL are here building blocks for glucose, aa, triglyceride, 3. Regeneration of RuBP - takes PGAL leftovers and remake the RuBP into an organic molecule Section 5.6 © McGraw Hill, LLC 23  Calvin Cycle = Carbon reactions All plants use the Calvin cycle (C3 pathway) to make glucose Carbon fixation: Carbon is removed from molecules of CO2 CO2 combines with (phosphorylated 5-carbon sugar) RuBP ( Ribulose BisPhosphate). This reaction is catalyzed by the RUBISCO enzyme (ribulose bisphosphate carboxylase oxygenase) – the most abundant protein/enzyme on earth). The resulting 6-carbon compound is unstable and breaks down into two molecules of 3-PhosphoGlyceric Acid (PGA). PGAL Synthesis – The PGA molecules are further phosphorylated (by ATP) and are reduced (by NADPH) to form PhosphoGlycerAldehyde (PGAL). PGAL. serves as the starting material for the synthesis of glucose, and fructose. Glucose and fructose make the disaccharide sucrose, which travels in solution to other parts of the plant (e.g., fruit, roots). Glucose is also the monomer used in the synthesis of polysaccharides starch & cellulose Regeneration of RuBP -- takes PGAL leftovers and remakes the RuBP - an organic molecule © McGraw Hill, LLC 24  Clicker question #5 How does a plant cell use the ATP that it produces in the light reactions? A. to fuel processes and reactions throughout the cell B. to fuel the Carbon reactions/Calvin Cycle C. to break down glucose D. to convert NADP+ To NADPH © McGraw Hill, LLC 25  5.5 Mastering concepts What are the roles of CO2, ATP, and NADPH in the Calvin cycle? © McGraw Hill, LLC 26  Plants use different carbon fixation pathways C3 plants C 4 plants, and CAM plants each do photosynthesis, using different pathways for fixing carbon. Each has its own advantages and disadvantages, depending on the environment the plant is in. We have been studying C3 photosynthesis, which is used by most plant species, such as this sycamore tree. Section 5.6 Figure 5.13 © McGraw Hill, LLC 27  Carbon fixation pathways are plant adaptations C3 plants do well in cool, C4 and CAM (Crassulacean Acid Metabolism) plants moist weather. are adapted to hot, dry weather. Section 5.7 Access the text alternative for slide images. Figure 5.12 © McGraw Hill, LLC 28  C3 plants do photosynthesis all at once, in mesophyll cells Notice the different leaf anatomy In hot, dry weather, and Calvin cycle position. the stomata close to conserve water. Photorespiration occurs due to oxygen buildup inside the leaf, decreasing the efficiency of photosynthesis. C3 - All of the photosynthesis (light and Carbon reaction) occurs here in Mesophyll cells. Access the text alternative for slide images. Section 5.7 Figure 5.11 © McGraw Hill, LLC 29  C4 plants divide the labor between cells Light and carbon reactions occur in different cells. Carbon reactions occur away from oxygen to avoid photorespiration. Mesophyll cell Bundle sheath cell Flowering plants in hot, sunny environments use the C4 pathway. Carbon Rx occurs here. Light reactions occur here. Section 5.7 Figure 5.11 © McGraw Hill, LLC 30  CAM plants divide the labor temporally All reactions for photosynthesis occur in mesophyll cells. Carbon reactions occur only at night, in the cooler, moister air to avoid photorespiration. During the day, they finish the Calvin Cycle. Stomata closed to conserve water. Used by plants like cactus that live in desert conditions. Section 5.7 Access the text alternative for slide images. Figure 5.12 © McGraw Hill, LLC 31  Carbon Fixation Pathway are plant adaptations C3- C4- CAM about 95 percent of plants use the C3 pathway. C3 plants such as sycamore, in which carbon dioxide enters Calvin cycle in the mesophyll cell along with Rubisco to produce PGA (3 carbons) to produce sugar, and RuBP (Ribulose biphosphate) continues the cycle. About 5 percent of plants have adaptations that reduce photorespiration in hot, dry weather. C4 plants such as corn, in which during the day CO2 enters the mesophyll cell to form a 4-carbon molecule (Malate) and then enters the bundle-sheath cell to undergo Calvin cycle. CAM (Crassulacean Acid Metabolism) plant such as cactus, A CAM plant’s stomata open at night, when the temperature drops, and humidity rises. C O 2 diffuses in. Mesophyll cells incorporate the C O 2 into a 4-carbon compound (Malate) that is stored until the day in the vacuole. During the day, the molecule is moved to chloroplast and releases C O 2. This C O 2 is used for carbon fixation in the Calvin Cycle to produce sugar. © McGraw Hill, LLC 32  Investigating Life: Salamander embryos are solar powered This salamander produces embryos that are surrounded by a jelly layer. Algae live in the jelly coat, where they carry out photosynthesis. Photos: (a): Michelle Gilders/Alamy Stock Photo This benefits both organisms. Section 5.7 Figure 5.14 © McGraw Hill, LLC 33  Investigating Life: Salamander embryos benefit twice Embryos with a jelly coat receive oxygen from the algae. Researchers used radioactive labels to show that embryos also receive more (b, embryo): Renn Tumlison; (b, algae): Kim, Eunsoo, Yuan Lin, Ryan Kerney, Lili Blumenberg, and Cory Bishop. 2014. Phylogenetic analysis of algal symbionts associated with four North sugars from the algae American amphibian egg masses. PloS ONE, https://doi.org/10.1371/journal.pone.0108915 when grown in the light than in the dark. Section 5.7 Figure Access the text alternative for these images 5.14 © McGraw Hill, LLC 34