SBI4U1 2024 Unit 2 - Metabolic Processes - Lesson List PDF

SBI4U1 – 2024 UNIT 2 – METABOLIC PROCESSES – LESSON LIST LESSON TITLE HOMEWORK COMPLETED Overview of Cellular Respiration Chapter 3.1 (pages 126-140)...

SBI4U1 – 2024 UNIT 2 – METABOLIC PROCESSES – LESSON LIST LESSON TITLE HOMEWORK COMPLETED Overview of Cellular Respiration Chapter 3.1 (pages 126-140) Textbook: 1 Chapter 3.2 (pages 141-145) Page 160 (#3, 7, 7, 29, 39) Chapter 3.3 (pages 146-150) Page 171 (#2) Chapter 4.1 (pages 168-171) Worksheet: The Glycolysis Process Glycolysis & Pyruvate Oxidation 2 Chapter 4.2 (pages 172-182) Textbook: Page 182 (#1, 7a+b) Page 205 (#28) Worksheet: The Krebs Cycle The Krebs Cycle 3 Chapter 4.2 (pages 172-182) Textbook: Page 182 (#7c) Page 205 (#39) Worksheet: Oxidative Phosphorylation Oxidative Phosphorylation & Electron Transport Summary of Cellular 4 Chain Respiration Chapter 4.2 (pages 172-182) Textbook: Page 182 (#3, 4, 6, 9, 10) Anaerobic Cellular Respiration & Fermentation Textbook: 5 Chapter 4.4 (pages 190-194) Page 194 (#2, 3, 4, 5, 7, 8) Worksheet: 6 Cellular Respiration Summary Cellular Respiration Introduction to Photosynthesis Textbook: 7 Chapter 5.1 (pages 212-219) Page 219 (#1, 4, 5) Textbook: Light-Dependent Reactions Page 228 (#3) 8 Chapter 5.1 (pages 212-219) Page 245 (#4) Chapter 5.2 (pages 220-228) Page 246 (#5, 45, 46) Textbook: Calvin Cycle 9 Page 228 (#8, 10) Chapter 5.2 (pages 220-228) Page 247 (#47) Alterative Mechanisms – C4 & CAM Plant Worksheet: 10 Adaptations Alternate Mechanisms of Chapter 5.4 (pages 231-234) Carbon Fixation Worksheets: Comparing Photosynthesis and Cellular Photosynthesis & Comparison 11 Respiration Review Questions Chapter 5.6 (pages 237-240) Comparing Cellular Respiration and Photosynthesis **WATCH** INSERT TITLE HERE SBI4U1 – 2024 UNIT 2 – METABOLIC PROCESSES – EVALUATION LIST ASSESSMENT DESCRIPTION DUE DATE SUBMITTED 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Tylenol case study Exercise lab SBI4U1 – 2024 1. OVERVIEW OF CELLULAR RESPIRATION KEY TERMS Aerobic Cellular Redox Reactions Oxidation Reduction Glycolysis Pyruvate Oxidation Krebs Cycle Oxidative Phosphorylation Substrate-level Phosphorylation Oxidative Phosphorylation Coenzymes (Electron Carriers) Anerobic Pathways 1ST LAW OF THERMODYNAMICS The First Law of Thermodynamics states that: The total amount of energy in any closed system is constant Energy cannot be created or destroyed Can only be converted from one for to another If a physical system gains an amount of energy, another physical system must experience a loss of energy of the same amount By converting sunlight into chemical energy, green plants act as energy transformers For bonds between the atoms of reactants to break → energy must be absorbed When bonds are formed between atoms of products → energy will be released 2nd LAW OF THERMODYNAMICS The Second Law of Thermodynamics states that: In every energy transfer or conversion, some of the useful energy in the system becomes unusable and increases the entropy of the universe ENTROPY A measurement of disorder in a system Disorder increases when an orderly arrangement of objects becomes more randomly assorted An increase in entropy is usually associated with a breaking down of large particles into small particles, or the spreading out of particles 1 SBI4U1 – 2024 In chemical reactions, entropy increases when: 1) Solids react to form liquids or gases 2) Liquids react to form gaseous products 3) The total number of product molecules is greater than the total number of reactant molecules Exothermic Reactions – A chemical reaction in which energy is released, leaving the products with less chemical potential energy than the reactants Endothermic Reactions – A chemical reaction in which energy is absorbed, giving the products more chemical potential energy than the reactants 2 SBI4U1 – 2024 GIBBS FREE ENERGY Energy that is not lost and can do useful work Free energy is responsible for chemical and physical work within the body Change in free energy: ∆G = Gfinal state – Ginitial state Exergonic Reaction (-∆G) – A chemical reaction that releases free energy; the products have less free energy than the reactants o free energy of products < free energy of reactants o Free energy is released to do work; is spontaneous Endergonic Reaction (+∆G) – A chemical reaction that absorbs free energy; the products have more free energy than the reactants o free energy of products > free energy of reactants o Free energy is required to do work; is not spontaneous Cells can make endergonic reactions occur by coupling them with exergonic reactions o Energy coupling – the transfer of energy from one reaction to another in order to drive the second reaction Catabolic pathway – a pathway in which energy is released and complex molecules are broken down into simple molecules Anabolic pathway – a pathway in which energy is supplied to build complex molecules from simple molecules 3 SBI4U1 – 2024 AEROBIC CELLULAR RESPIRATION Occurs in the presence of oxygen A series of redox reactions o Glucose is oxidized to form carbon dioxide o Oxygen is reduced to form water Transfer of electrons important in the formation of ATP Electrons will move as part of the H atom through redox reactions o Movement of H atoms = movement of electrons Three overall goals of cellular respiration 1) break the bonds between the 6 atoms of carbon in glucose → forming 6 carbon dioxide 2) move hydrogen atom electrons from glucose to oxygen → form 6 water molecules 3) to trap as much of the free energy released in the process to form ATP Normally, the free energy that is available from the breakdown of glucose will be released through heat/light energy but body is able to trap that energy and store it as ATP ADENOSINE TRIPHOSPHATE (ATP) Types of Work Performed by ATP Mechanical Work Transport Work Chemical Work Beating of cilia or Process of pumping Process of supplying movement of flagella substances across chemical potential energy Contraction of muscle fibres membranes against their for non-spontaneous, Movement of chromosomes concentration gradient endergonic reactions, during mitosis/meiosis including protein synthesis and DNA replication 4 SBI4U1 – 2024 Structure – 3 parts: o Nitrogenous base (adenine) o 5-carbon sugar (ribose) o 3 phosphate groups Contains lots of free energy because of the 3 negatively charged phosphate Supplies energy directly to chemical reactions in all cells (mechanical, transport, chemical work) Universal energy currency in living organisms o Provides sufficient energy o Can couple to many different reactions o Can be assembled using energy from a variety of food molecules o Assembly and access is immediate ATP can couple many endergonic reactions through phosphorylation o The terminal phosphate group breaks away from ATP and transfers to the reactant molecule Cells generate ATP by combining ADP with Pi If ATP hydrolysis is an exergonic reaction, then the reverse process, ATP synthesis from ADP and Pi, is an endergonic reaction. Therefore, ATP synthesis requires the addition of free energy The energy needed to drive ATP synthesis usually comes from the exergonic breakdown of complex molecules containing an abundance of free energy. These complex molecules are in the foods we eat: carbohydrates, fats, and proteins o All of these molecules are sources of free energy. 5 SBI4U1 – 2024 ENZYMES AND ACTIVATION ENERGY Enzymes lower the amount of activation energy that reactants must overcome Without enzymes, metabolism would be very slow Even for exergonic reactions, it will not occur unless activation energy barrier is overcome for bonds to be broken Rate of the reaction is proportional to the number of reactant molecules that can overcome the activation barrier to reach the transition state. o When the enzymes lower the activation energy barrier, more reactant molecules can reach the transition state at a faster rate. o ∆G is unaffected by the enzyme Enzymes reduce activation energy (3 mechanisms): 1) Bring molecules together (Figure a) Substrate molecules need to collide with each other to reach the transition state When both substrate molecules bind to the enzyme, they are in an ideal proximity and orientation for catalysis to occur. 2) Expose reactant molecules to altered charged environments (Figure b) The active site of some enzymes contains ionic groups with positive or negative charges that attract and/or repel parts of the substrate. This stresses bonds in a way that favours catalysis. 3) Change shape of substrate (Figure c) The active site of the enzyme can strain or distort the substrate molecule, which weakens its chemical bonds. This reduces the amount of energy required to break the bonds. This mechanism of enzyme- substrate interaction is called the induced-fit model. 6 SBI4U1 – 2024 THE FOUR MAIN STAGES OF AEROBIC CELLULAR RESPIRATION 1) Glycolysis 2) Pyruvate Oxidation 3) Krebs Cycle (also known as Citric Acid Cycle (CAC) or Tricarboxylic Acid (TCA) Cycle) 4) Oxidative Phosphorylation Each stage involves the transfer of energy which occurs in one of two ways o Substrate-level phosphorylation o Oxidative phosphorylation 7 SBI4U1 – 2024 SUBSTRATE-LEVEL PHOSPHORYLATION Forms enzymes through enzyme-catalyzed reactions Helps to transfer of a phosphate group from a phosphoenolpyruvate (PEP) directly to an ADP to form ATP A small number of ATP is made this way from one glucose molecule during cellular respiration OXIDATIVE PHOSPHORYLATION Process that forms ATP using energy transferred indirectly from a series of redox reactions o A series of redox reactions that occur in the mitochondria Involves two important coenzymes (electron carriers); NAD + and FAD2+, that help to transfer electrons from glucose to indirectly make ATP NAD+: reduced to form NADH + H+ Carries two electrons and only one proton; the other proton is dissolved into the aqueous solution FAD2+: reduced to form FADH2 NAD+ and FAD2+ removes 2 hydrogen atoms from glucose and brings them to get passed down a series of electron acceptors. o NAD+ and FAD2+ are reduced at different points of the process and occur multiple times Oxygen is the final electron acceptor …what does it form? The figure below demonstrates Oxidative Phosphorylation. 8 SBI4U1 – 2024 THE MITOCHONDRION (POWERHOUSE OF THE ??) Glycolysis occurs in the cytosol Pyruvate oxidation, the Krebs cycle, and Oxidative Phosphorylation occurs in the mitochondria o Site where most of the ATP for the body is produced Composed of two membranes (outer and inner membrane) o Intermembrane space: between outer and inner membrane o Matrix: the interior aqueous environment Some prokaryotes do not have mitochondria – cellular respiration occurs in the cytosol except oxidative phosphorylation occurs on internal membranes ANAEROBIC PROCESSES Anaerobic Respiration – A process that uses a final inorganic oxidizing agent other than oxygen to produce energy Energy is extracted in the absence of oxygen; anaerobic respiration and fermentation 9 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 3 on page 160 of your textbook: #3, 7, 8, 29, 29 3. Which step is necessary for the initiation of a chemical reaction? a) new bonds must form b) bonds must be broken c) water must be added d) oxygen must be added 7. ATP synthesis is which of the following: a) an endergonic process that phosphorylates ADP b) an exergonic process that phosphorylates ADP c) an endergonic process that dephosphorylates ATP d) an exergonic process that dephosphorylates ATP 8. in which component of a coupled reaction is there a release of free energy? a) hydrolysis of ATP b) ADP phosphorylation c) ATP synthesis d) ADP Synthesis 29. Summarize the three ways that an enzyme can help a reactant molecule reach the transition state. 39. Explain why photosynthesis is an example of an endergonic reaction. Complete the following questions from Chapter 4.1 on page 171 of your textbook: #2 2. Explain the main difference between aerobic respiration and anaerobic respiration. 10 SBI4U1 – 2024 2. GLYCOLYSIS & PYRUVATE OXIDATION “Glyco” + “lysis” First set of reactions for extracting energy from sugar molecules Splitting of glucose (sugar) From 6-Carbon sugar to two 3-Carbon sugar Occurs in the cytosol 10 STEP PROCESS Two major phases. Both phases have 5 steps. 1. Energy investment phase 2. Energy payoff phase NOTE: Figure 2 on the next page (found on page 173 of the textbook) is a summarized image of the entire Glycolysis process. Throughout this note, you will learn about each individual step. Use Figure 2 as a summary of the process when studying. 11 SBI4U1 – 2024 Figure 2: The reactions of glycolysis, including the initial five-step energy investment phase followed by the five-step energy payoff phase. Because two molecules of G3P are produced in reaction 5, all the reactions from 6 to 10 are doubled (not shown). The names of the enzymes that catalyze each reaction are in red. 12 SBI4U1 – 2024 ENERGY INVESTMENT PHASE STEP 1 Carbon 6 is phosphorylated using ATP to prevent glucose from leaving the cell Reaction type – Phosphorylation Enzyme – hexokinase Energy – absorbed STEP 2 Glucose 6-phosphate is rearranged to form fructose 6-phosphate Reaction type – Isomerization Enzyme – phosphoglucoisomerase Energy – equilibrium 13 SBI4U1 – 2024 STEP 3 Second phosphorylation occurs to form an energetically unstable fructose 1,6-bisphosphate Reaction type – Phosphorylation Enzyme – phosphofructokinase Energy – absorbed STEP 4 The molecule is unstable so it is split into two smaller molecules Reaction type – Lysis (cleavage) Enzyme – adolase Energy – equilibrium STEP 5 Dihydroxyacetone phosphate (DHAP) is immediately converted to glyceraldehyde 3-phosphate (G3P) Reaction type – Isomerization Enzyme – triosephosphate isomerase Energy – equilibrium Only G3P continues in glycolysis; steps 4 and 5 occur simultaneously ENERGY PAYOFF PHASE 14 SBI4U1 – 2024 STEP 6 Transfers electrons from G3P to reduce NAD+ to NADH, coupled with the addition of an inorganic phosphate group to oxidize G3P to form 1,3- bisphosphoglycerate (BGP) Reaction type – Redox and phosphorylation Enzyme – triosephosphate dehydrogenase Energy – released STEP 7 ADP phosphorylation to create ATP Reaction type – Substrate-level phosphorylation Enzyme – phosphoglycerate kinase Energy – released STEP 8 Phosphate moved from carbon 3 to carbon 2 Reaction type – Isomerization Enzyme – phosphoglucomutase Energy – equilibrium STEP 9 H2O is removed to set up the next reaction Removal of water forms phosphoenolpyruvate (PEP) with high-energy phosphate bonds Reaction type – Dehydration Enzyme – enolase Energy – equilibrium 15 SBI4U1 – 2024 STEP 10 ADP is phosphorylated to ATP from PEP to form pyruvate Reaction type – Substrate-level phosphorylation Enzyme – pyruvate kinase Energy – released GLYCOLYSIS SUMMARY Starting reactants – Glucose + 4 ADP + 4 Pi + 2 ATP + 2 NAD+ Final products – 2 Pyruvates + 2 ADP + 4 ATP + 2 NADH ATP count – 2 used; 4 produced NADH count – 2 produced PYRUVATE OXIDATION The two molecules of pyruvate that are synthesized by glycolysis still contain approximately 75% of the energy found in one molecule of glucose. The extraction of the remaining free energy in pyruvate continues via pyruvate oxidation and the citric acid cycle In these reactions, more ATP and more of the electron carriers NADH and FADH2 are formed, while the remaining glucose is completely oxidized. Carbon is released in the form of waste CO2. 16 SBI4U1 – 2024 In the presence of oxygen, pyruvate is transported into the mitochondria 3 step process: 1) Decarboxylation occurs to remove a carboxyl group as CO2 2) NAD+ comes in to oxidize the remaining 2-Carbon molecule to form NADH + H+; the intermediate molecule formed is called acetic acid (acetate) 3) A coenzyme known as coenzyme A (CoA) is added to the molecule to form Acetyl CoA Process is irreversible and facilitated by the enzyme pyruvate dehydrogenase o Enzyme is regulated allosterically Overall Equation: 2 pyruvate + 2 NAD+ + 2 CoA → 2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2 17 SBI4U1 – 2024 Acetyl-CoA Almost all macromolecules is converted into acetyl-CoA to be catabolized for energy o Can be catabolized into fat or ATP If the body needs energy: o Acetyl-CoA moves on to the next stage of cellular respiration (Krebs Cycle) If the body does not need the energy: o Acetyl-CoA is anabolized into lipids to store the energy as fat 18 SBI4U1 – 2024 HOMEWORK: THE GLYCOLYSIS PROCESS Label the following diagram with the product at the end of each step of the glycolysis process. 19 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 4.2 on page 182 of your textbook: #1,7a + b. 1. Why is glycolysis considered to be the most fundamental and probably the most ancient of all metabolic pathways? 7. Write the overall chemical equation for: a) Glycolysis: b) Pyruvate Oxidation: Complete the following questions from Chapter 4 on page 205 of your textbook: #28 28. Glycolysis begins with glucose, yet many animals can survive on diets that are extremely low in carbohydrates. Account for this observation. 20 SBI4U1 – 2024 3. KREBS CYCLE RECALL: CELLULAR RESPIRATION 1. What are the reduced forms of NAD+ and FAD? NADH and FADH2 2. What are the products of glycolysis? 2 Pyruvates + 2 ADP + 4 ATP + 2 NADH 3. Fructose 6-phosphate is phosphorylated by what enzyme? Phosphofructokinase 1 glucose = 2 pyruvate = 2 acetyl-CoA KREBS CYCLE Is a cyclical process o The product of the last step will become a reactant in step 1 For each turn of Krebs cycle: o Two carbons of acetyl-CoA will enter the cycle o Two different carbons will exit as waste in the form of CO2 o 3 NADH and 1 FADH2 are formed o One ATP is made by substrate-level phosphorylation 21 SBI4U1 – 2024 STEP 1 Acetyl-CoA is broken off into a 2 Carbon acetyl group and Coenzyme A The acetyl group (2C) bonds to an oxaloacetate (4C) to form citrate (6C) Reaction type – Condensation Enzyme – citrate synthetase Energy – absorbed STEP 2 There is a rearrangement of atoms with the help of H 2O Citrate is rearranged into its isomer, isocitrate Reaction type – Isomerization Enzyme – aconitase Energy – equilibrium STEP 3 Isocitrate loses a carbon atom to form a α-ketoglutarate (5C), releasing CO2 α-ketoglutarate is oxidized and NAD+ is reduced to form NADH + H+ Reaction type – Decarboxylation + redox Enzyme – isocitrate dehydrogenase Energy – released STEP 4 Coenzyme A returns and bonds to α-ketoglutarate (5C) to form succinyl-CoA (4C) Another CO2 is removed and NAD+ is oxidized Reaction type – Synthesis + decarboxylation + redox Enzyme – α-ketoglutarate dehydrogenase Energy – released 22 SBI4U1 – 2024 STEP 5 Released of CoA from succinyl-CoA (4C) is coupled with the phosphorylation of ADP forms ATP and succinate (4C) Note that this is the only time ATP is formed in the Krebs cycle and the phosphate group is taken from GTP Reaction type – Substrate-level phosphorylation Enzyme – succinyl-CoA Energy – released STEP 6 Succinate (4C) is oxidized with the reduction of FAD to form fumarate (4C) and FADH2 Reaction type – Redox Enzyme – succinate dehydrogenase Energy – released STEP 7 H2O is added into the fumarate (4C) to form malate (4C) in preparation for the next reaction Reaction type – Hydration Enzyme – fumarase Energy – absorbed STEP 8 Malate (4C) is oxidized to form oxaloacetate (4C) and NAD+ is reduced Reaction type – Redox Enzyme – malate dehydrogenase Energy – released 23 SBI4U1 – 2024 KREBS CYCLE SUMMARY So far, from one glucose molecule… 24 SBI4U1 – 2024 HOMEWORK: THE KREBS CYCLE Label the following diagram with the product at the end of each step of the Krebs Cycle. 25 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 4.2 on page 182 of your textbook: #7c. 7. Write the overall chemical equation for: c) Citric Acid Cycle: Complete the following questions from Chapter 4 on page 205 of your textbook: #39 39. Summarize the citric acid cycle. Include both the reactants and products that result from each molecule of glucose that enters the cycle. Also include diagrams. 26 SBI4U1 – 2024 4. OXIDATIVE PHOSPHORYLATION & ELECTRON TRANSPORT CHAIN RECALL: Cellular Respiration 1. What happens during the redox and decarboxylation reaction when Isocitrate (6C) forms α- ketoglutarate (5C)? NAD+ is reduced to form NADH and the release of a CO2 molecule 2. How many ATPs are formed during the Krebs cycle (1 glucose molecule)? 2 3. Why is the Krebs cycle considered a cyclic process? The final product (oxaloacetate) becomes the reactants for another round of the Kreb’s cycle 4. List the two ways ATP is formed during cellular respiration? Substrate-level phosphorylation and Oxidative phosphorylation TWO METHODS OF ATP SYNTHESIS 1) SUBSTRATE-LEVEL PHOSPHORYLATION Enzyme transfers a phosphate group from a substrate molecule to ADP Occurs during glycolysis & Krebs cycle 27 SBI4U1 – 2024 2) OXIDATIVE PHOSPHORYLATION Couples 2 processes that occur on the inner mitochondria membrane (IMM): 1. Oxidation of NADH and FADH2 by the electron transport chain (ETC) o Energy in electrons of NADH and FADH2 are used to drive the H+ against its concentration gradient o Electrons will move along the mitochondrial membrane until it finally binds with oxygen (final electron acceptor) and converted into water 2. Phosphorylation through the process of chemiosmosis o H+ will passively diffuse back into the mitochondria matrix through an enzyme called ATP synthase to drive the synthesis of ATP Co-Enzymes The NADH and FADH2 formed so far will be oxidized as they transfer the H + and electrons they have acquired to a series of compounds along the IMM When NAD+ was reduced, it gained one H+ and two electrons; forms NADH When FAD was reduced, it gained two H+ and two electrons; forms FADH2 As they become oxidized, they will transfer the electrons one by one on to the ETC, as the H+ is released into the matrix ELECTRON TRANSPORT CHAIN The electron transport chain comprises a system of components that, in eukaryotes, occurs on the inner mitochondrial membrane Facilitates the transfer of electrons from NADH and FADH2 to O2 Consists of four protein complexes: Complex I, NADH dehydrogenase Complex II, succinate dehydrogenase Complex III, cytochrome complex Complex IV, cytochrome oxidase Transfer of electrons between protein complexes facilitated by two mobile electron shuttles o Ubiquinone (Q), shuttles electrons from complex I and II to complex III o Cytochrome C (Cyt C), shuttles electrons from complex III to complex IV 28 SBI4U1 – 2024 ETC AND OXYGEN Electronegativity – Is the tendency to attract a shared pair of electrons towards itself The electrons will move down the ETC Final electron acceptor is the very electronegative oxygen Oxygen drives the redox reactions Lack of oxygen will prevent this entire process from occurring NADH PATHWAY: COMPLEX I (NADH dehydrogenase) NADH is oxidized and transfers its electrons to Complex I A H+ ion is pumped across the IMM through the protein complex Current number of H+ pumped per NADH= 1 NADH PATHWAY: UBIQUINONE (Q) Electron is transferred from Complex I to ubiquinone (Q) Q is a hydrophobic lipid that moves within the phospholipid bilayer NADH PATHWAY: COMPLEX III (CYTOCHROME COMPLEX) Electron is transferred from Q to Complex III Another H+ is pumped across the IMM Current number of H+ pumped per NADH = 2 NADH PATHWAY: CYTOCHROME C (CYT C) Electrons are transferred from Complex III to cytochrome C (Cyt C) Cyt C is a mobile component located on the surface of the IMM in the intermembrane space 29 SBI4U1 – 2024 NADH PATHWAY: COMPLEX IV (CYTOCHROME OXIDASE) Electrons are transferred from Cyt C to Complex IV Another H+ is pumped across the IMM by Complex IV Final total number of H+ pumped per NADH= 3 NADH PATHWAY: O2 O2 is the final electron acceptor of the ETC Enough electrons pass through the ETC to produce a single full H 2O molecule Oxygen is most electronegative Without oxygen, entre thing would come into a halt (suffocation) FADH2 PATHWAY: COMPLEX FADH2 PATHWAY: COMPLEX II (SUCCINATE DEHYDROGENASE) FADH2 is oxidized and the electrons are transferred to Complex II Electrons are transferred from Complex II to Q and will process through the rest of the ETC Note: complex protein is a single peripheral membrane protein located on the side of the matrix No protons are pumped across the IMM at this stage 30 SBI4U1 – 2024 ELECTROCHEMICAL PROTON GRADIENT: CHEMIOSMOSIS 1. A chemical gradient exists because the concentration of H+ is not equal 2. Because H+ have a positive charge, they repel from each other and are more attracted to the negative side (matrix) Hydro dam Takes advantage of the electrochemical proton gradient to drive the movement of H + back down its concentration gradient through the protein complex called ATP Synthase CHEMIOSMOSIS Proton motive force o Facilitated diffusion of proton back down its electrochemical concentration gradient For every NADH → 3 H+ are pumped out → 3 ATP molecules are formed For every FADH2 → 2 H+ are pumped out → 2 ATP molecules are formed ATP SYNTHASE (COMPLEX V) The formation of ATP through oxidative phosphorylation is through the large multi-protein complex called ATP Synthase Consists of two units: o Basal unit (F0): embedded in the IMM o Headpiece (F1): extends into the mitochondrial matrix Basal unit forms a channel that H+ ions can move through freely The flow of H+ ions powers the rotation of the headpiece which catalyzes the phosphorylation of ADP to ATP!! 31 SBI4U1 – 2024 UNCOUPLING ELECTRON TRANSPORT Some cells have uncoupling proteins present in the IMM and provides H+ with an alternative pathway to re-enter the matrix without going through ATP Synthase This pathway does not produce any ATP but still produces energy, but in the form of thermal energy Brown adipose tissue are an example of such cells that contain uncoupling proteins Important for maintaining body temperature especially for hibernating mammals, or animals that need excess thermal energy in cold environments, or very young infants Example: Bears are able to hibernate because cells in some of their tissues can uncouple the electron transport chain and chemiosmosis to produce thermal energy So far, from ONE glucose molecule… 32 SBI4U1 – 2024 33 SBI4U1 – 2024 HOMEWORK: OXIDATIVE PHOSPHORYLATION Label the following diagram with the products during Oxidative Phosphorylation. Then complete the chart. ATP NADH FADH2 CO2 Glycolysis Pyruvate Oxidation Krebs Cyle TOTAL Conversion in ETC FINAL ATP COUNT 34 SBI4U1 – 2024 HOMEWORK: SUMMARY OF CELLULAR RESPIRATION Summarize the inputs (reactants) and the outputs (products) of cellular respiration. Compare the reactants and products in the table with the figures that illustrate the various stages. ETC and Glycolysis Pyruvate Oxidation Krebs Cycle chemiosmosis (per glucose) (per glucose) (per glucose) (per glucose) Location Reactants Products ATP required ATP produced Net ATP produced 35 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 4.2 on page 182 of your textbook: #3, 4 ,6, 9, 10. 3. Glycolysis, pyruvate oxidation, and the citric acid cycle produce only a small amount of ATP from the energy in a glucose molecule. In what form(s) is (are) the rest of the harvestable energy that is converted to ATP in the electron transport chain and chemiosmosis? 4. How does the electron transport chain produce ATP? What is the driving force? 6. Which stages of aerobic cellular respiration occur in the mitochondria, and which stages do not? 9. What is the primary function of the proton-motive force? 10. Give an example of how uncoupling is used by organisms to increase survival. 36 SBI4U1 – 2024 5. ANAEROBIC CELLULAR RESPIRATION & FERMENTATION ANAEROBIC RESPIRATION Occurs in the absence of oxygen Two types – lactic acid fermentation + ethanol fermentation Oxygen present – pyruvate will proceed into mitochondria Oxygen absent – pyruvate will stay in the cytoplasm o Cells will only utilize glycolysis to produce ATP FATE OF PYRUVATE 37 SBI4U1 – 2024 FERMENTATION Processes are coupled reactions: glycolysis + “a reaction to regenerate NAD +” Lactic acid fermentation o Pyruvate is reduced directly to form lactate Ethanol/Alcohol fermentation o Pyruvate is converted into ethanol in a two-step process LACTIC ACID FERMENTAITON Occurs during strenuous exercise (increased in ATP demand) Oxygen is not delivered fast enough to facilitate oxidative phosphorylation o Increased NADH concentration Body moves to plan B → lactic acid fermentation Since there is a build-up of NADH, it can directly be oxidized by pyruvate o Forms lactate and NAD+ o NAD+ can cycle back to be used again in glycolysis Fast but low production method of producing ATP! 38 SBI4U1 – 2024 As mentioned, lactic acid fermentation is a quick (but less efficient) method of generating ATP o Constant supply of NAD+ allows for a quicker rate of glycolysis to occur Once believed that the build up of lactic acid after strenuous exercise was the cause of muscle stiffness and soreness o After oxygen levels rise back up to normal levels, the reaction is reversed o Lactic acid is converted back into pyruvate; NAD+ is reduced back into NADH ▪ Both will proceed to the next step of aerobic respirate Occurs in some fungi and bacteria o Used in dairy industry to make cheese and yogurt Occurs in humans during anaerobic conditions o What could we be doing to force our cells to go through anaerobic conditions? ETHANOL FERMENTATION Two step process: 1. Pyruvate (3C) is decarboxylated to form acetaldehyde (2C) o CO2 is removed 2. Acetaldehyde (2C) is reduced to form ethanol (2C) o NADH is oxidized into NAD+ Similar to lactic acid fermentation, this regenerates the supply NAD+ for glycolysis Occurs in yeast (and other organisms that lack mitochondria) Used largely in breweries and wineries 39 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 4.4 on page 194 of your textbook: #2, 3, 4, 5, 7, 8. 2. a) What is the difference between fermentation and glycolysis?' b) Why do cells rely on fermentation rather than glycolysis alone? 3. Describe one advantage and one disadvantage of a species that is able to perform fermentation. How do the advantage and disadvantage influence the energy efficiency of the species and where the species can live? 4. a) Explain the anaerobic pathway that is used to create a loaf of bread. How does this pathway work? b) Name two other products that use the same pathway. c) Explain this pathway to someone who routinely bakes but is not a scientist. 5. Do our muscle cells produce alcohol? Given that alcohol and lactate fermentation both yield two ATP molecules for every glucose molecule, do you think it would make any difference which pathway was used? Explain. 40 SBI4U1 – 2024 7. Using what you know about lactic acid fermentation, explain why a person could not perform strenuous exercise indefinitely. 8. How could you increase the amount of time that you can exercise comfortably? 41 SBI4U1 – 2024 6. CELLULAR RESPIRATION SUMMARY The following worksheets will help you summarize all of the information learned during lessons 1 – 5 of this unit. HOMEWORK: CELLULAR RESPIRATION 1. Write the balanced word and chemical equation for aerobic respiration. 2. What is the purpose of cellular respiration? 3. Why is NADH called an electron shuttle bus? 4. What are the two mechanisms in which ATP is generated? Briefly describe each mechanism. 5. Make a comparison chart to show how much ATP is produced from substrate level phosphorylation versus oxidative phosphorylation (use the equivalent amount of ATP for coenzymes). 42 SBI4U1 – 2024 6. Define the following terms: Aerobic Cellular Respiration: Anaerobic Cellular Respiration: Substrate-level Phosphorylation: Oxidative Phosphorylation: Chemiosmosis: Carboxylation: 7. Identify two instances where carboxylation occurs during cellular respiration. 8. What role do the following molecules have in cellular respiration: a) NADH & FADH2 b) Hydrogen Ions c) Acetyl-CoA 43 SBI4U1 – 2024 d) Electrons e) Oxygen 9. a) What is the purpose of glycolysis? b) What are the products of glycolysis? c)What gets oxidized? Reduced? 10. a) What are the products of one turn of Krebs cycle? b) How many turns of the Krebs cycle are required to metabolize one molecule of glucose? 44 SBI4U1 – 2024 11. Draw a diagram of a mitochondria and label its parts. 12. What happens to pyruvic acid before it enters the Krebs cycle? 13. What happens to the substance entering the Krebs cycle? 14. During Krebs, what products are formed? How many for one molecule of glucose? 15. How is the electron transport chain organized, and what is its purpose? Draw a labeled sketch that shows all of the protein complexes, energy molecules, electron movement, protons and location. 45 SBI4U1 – 2024 16. Where is the H+ reservoir located in the mitochondria? Indicate where each part of cellular respiration occurs. 17. What happens to the electrons as they are passed along the electron chain? 18. Explain how ATP is made by chemiosmosis. 19. At what point on the ETC do the electrons stop from getting passed on? 20. What happens to theses electrons after that point? 21. What happens to the NAD+ and FAD after it gives electrons to the ETC? 22. What is the significance of the inner membrane and intramembrane space in the mitochondria? 46 SBI4U1 – 2024 23. Compare alcoholic fermentation and lactic acid fermentation in terms of where it occurs, starting substrate, end products, and amount of energy produced. 24. When does fermentation occur? 25. What is being oxidized and reduced in fermentation? Contrast this to pyruvate oxidation and Krebs cycle phase. 26. What are the differences between alcoholic fermentation and lactic acid fermentation? 47 SBI4U1 – 2024 48 SBI4U1 – 2024 7. INTRODUCTION TO PHOTOSYNTHESIS Purpose – Use energy from light to convert inorganic compounds into organic fuels that stored potential energy in their carbon bonds CO2 + H2O → C6H12O6 + O2 Photosynthesis and cellular respiration are COMPLEMENTARY processes AUTOTROPHS Organisms that obtain energy without needing to ingest other organisms Require the input of inorganic substances from the environment Photoautotrophs – Use light energy (photons) CHLOROPLASTS Both reactions take place here Composed of: 1. Outer membrane – Covers the entire surface of the organelle 2. Inner membrane – Lies just inside the outer membrane 3. Stroma (aqueous fluid) – enzymes located inside the stroma of the chloroplast catalyzes the reactions of the Calvin Cycle 4. Thylakoid membrane (or thylakoids) – Third membrane system o Where light dependent reactions of photosynthesis occur o Gives leaves their green colour because of chlorophyll and other accessory pigments embedded within 5. Grana (singular: granum) – Interconnected stacks of flattened discs formed by the thylakoid 49 SBI4U1 – 2024 NATURE OF LIGHT Light is a form of energy with different wavelengths The shorter the wavelength, the greater the energy of each photon of light Certain wavelengths of light are detectable by human eyes Visible light drives photosynthesis The Electromagnetic Spectrum LIGHT ABSORBING PIGMENTS Pigment – groups of molecules that absorb light Chlorophyll – pigments found in green plants The colour of the pigments is due to wavelengths of light reflecting back into our eyes Chlorophyll: o Green pigment o Absorbs mainly blue and red wavelengths of light o Reflect back green Carotenoids: o Pigments that absorb mainly blue and green o Reflect back orange and red o Help dissipate excessive light energy that would otherwise damage chlorophyll In the fall chlorophyll pigments breakdown first leaving carotenoids which allow the reflection of orange and red wavelengths 50 SBI4U1 – 2024 Chlorophyll o Chlorophyll a Reaction centre o Chlorophyll b Antenna complex Carotenoids Reaction centre – donates an electron to the primary electron acceptor Antenna complex – these are accessory pigments that will capture light but transfer them to the reaction centre CAPTURING LIGHT Three possible outcomes once a photon excites an electron: 1. The excited electron returns to its ground state o Energy released as thermal and/or fluorescence 2. Energy from the excited electron is transferred to a neighbouring electron o Original electron is returned to its ground state 3. Excited electron is transferred to an electron-accepting molecule o Electron-accepting molecule is known as a primary electron acceptor o This outcomes proceeds to the next step of photosynthesis 51 SBI4U1 – 2024 PHOTOSYNTHESIS Occurs in photosynthetic eukaryotes o Cells contain chloroplasts “Photo” o Light-dependent reactions (LIGHT REACTION) o Takes place in the thylakoid membrane “Synthesis” o Calvin Cycle (NOT “DARK” REACTION) o Occurs in the stroma 52 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 5.1 on page 219 of your textbook: #1, 4, 5 1. Why are photoautotrophs considered to be primary producers? 4. a) Would you expect these species to contain more or less chlorophyll than green algae? Why? b) Would you expect these species to perform photosynthesis more efficiently under a green light source or a red light source? Explain your reasoning. c) Things tend to look bluish underwater because water absorbs red light more effectively than blue light. How might this fact help account for the characteristics of the deep-water species of algae? 5. What are the thylakoids? Why are they important for photosynthesis? 53 SBI4U1 – 2024 8. LIGHT-DEPENDENT REACTIONS THE TWO STAGES OF PHOTOSYNTHESIS 1) Light Dependent Reactions – the first stage of photosynthesis, during which water molecules are split as light energy is absorbed and transformed into chemical energy in ATP and NADPH 2) Light Independent Reactions (aka The Calvin Cycle) – The second stage of the photosynthesis process that uses ATP and NADPH to convert CO2 to sugars LIGHT REACTION What is the main purpose of the light reactions? Input – Light (photon), Water Output – Oxygen, ATP, NADPH PHOTOEXCITATION When atoms absorb energy from the sun, electrons gain energy and become “excited” Three different scenarios can occur: 1) Electron returns to its ground state and emits a less energetic photon or as thermal energy 2) Returns to its ground state and the energy released is used to excite an electron of a neighbouring molecule 3) The excited electron is accepted by an electron- accepting molecule 54 SBI4U1 – 2024 PHOTOSYSTEMS Embedded in the transmembrane protein of the thylakoid membrane Composed of the antenna complex of proteins and pigments that surrounds a reaction center The reaction center contains a chlorophyll-a that is located next to a primary electron acceptor PHOTOSYSTEM MECHANISM Light (photon) excites an electron on the reaction center chlorophyll-a Primary electron acceptor traps the high energy electron before it can return to ground state Photosystem II – reaction center contains the specialized chlorophyll-a molecules known as P680 Photosystem I – reaction center contains P700 chlorophyll-a molecules Numbers refer to the wavelength of light they absorb optimally In photosynthesis, the actions of PSII occurs before PSI o Their names were based on the order of their discovery 55 SBI4U1 – 2024 THYLAKOID PROTEINS: PSII (P680) PSII absorbs light Excited electron in the reaction center chlorophyll (P680) is captured by the primary electron acceptor P680 that has lost an electron is oxidized and becomes P680+ P680+ is a very electronegative and will rip the electrons out of a water molecule o This process is facilitated by an enzyme subunit, water-splitting complex THYLAKOID PROTEINS: PLASTOQUINONE (Pq) Electron captured by the primary electron acceptor of PSII will now be passed through an electron transport chain The electron is first transferred to plastoquinone (Pq) As Pq accepts an electron, it will also gains H+ from the stroma Pq is a mobile component within the thylakoid membrane First electron acceptor → ETC Pq will take electron and protons THYLAKOID PROTEINS: CYTOCHROME COMPLEX Electrons are transferred from Pq to cytochrome complex Protons are pumped from the stroma across the thylakoid membrane, and into the lumen THYLAKOID PROTEINS: PLASTOCYANIN (Pc) Electrons are transferred to plastocyanin (Pc) Pc is another mobile carrier that will shuttle electrons from the cytochrome complex to the next complex Pc is located on the lumen side of the thylakoid membrane 56 SBI4U1 – 2024 THYLAKOID PROTEINS: PSI (P700) Simultaneously, electrons on P700 are also excited by light and captured by its own primary electron acceptor, leaving it oxidized (P700 +) The electrons transferred from Pc to P700 will replace the electrons that were lost and reduced into its original state THYLAKOID PROTEINS: FERRODOXIN (Fd) Electrons undergo a second electron transport chain Electrons are transferred from PSI to ferrodoxin Ferrodoxin is an iron containing mobile component located on the stromal side of the thylakoid membrane THYLAKOID PROTEIN: NADP+ REDUCTASE Fd will transfer it’s electron to NADP+ reductase to reduce a NADP+ into NADP NADP+ is our final electron acceptor in photosynthesis Another Fd will transfer a second electron to NADP with the addition of a H+ and further reduce into NADPH REPLACING LOST ELECTRONS Electrons on PS1 that were lost are replaced by the electrons that came originally from PSII Electrons on PSII that were lost are replaced by extracting the electrons from water 57 SBI4U1 – 2024 Refer to page 222 of the textbook for an additional explanation of the processes involved PHOTOPHOSPHORYLATION Light dependent formation of ATP by chemiosmosis ATP synthesis is similar to the mechanism in cellular respiration ATP is produced in the stroma 58 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 5.2 on page 228 of your textbook: #3. 3. Why is light energy essential for photosynthesis to occur? Complete the following questions from Chapter 5 on page 245 of your textbook: #4. 4. Which molecule oxidizes water in photosystem II? (a) P680 (b) P680* (c) P700 (d) P680+ Complete the following questions from Chapter 5 on page 246 of your textbook: #5, 45, 46 5. What is chemiosmosis in a chloroplast primarily responsible for? (5.2) K/U (a) hydrolysis of water (b) establishment of a proton gradient (c) recovery of NADP+ (d) synthesis of ATP 45. What drives the electron transport chain in photosystem I and photosystem II? 46. Briefly define and summarize the process of chemiosmosis. 59 SBI4U1 – 2024 9. CALVIN CYCLE LIGHT DEPENDENT REACTIONS Water is split to produce O2 (released from cell) and H+ ions (released into lumen) Electron transport chain helps establish electrochemical proton gradient Photophosphorylation – light-dependent formation of ATP by chemiosmosis NADP+ is the final electron acceptor and produces NADPH TYPES OF ELECTRON TRANSPORT MECHANISMS 1. Non-cyclic electron flow 2. Cyclic electron flow Ferrodoxin has 2 possible fates o Transfer of electrons to NADP+ reductase (non-cyclic flow) o Transfer electrons to plastoquinone (cyclic flow) CYCLIC ELECTRON FLOW Only involves PSI (P700) Ferrodoxin returns electrons back to Pq Additional H+ can be pumped into the lumen to aid in the formation of the electrochemical proton gradient o Which will help to generate more ATP Note that this cyclic pathway does not produce more NADPH 60 SBI4U1 – 2024 Non-cyclic electron flow produces roughly an equal amount of ATP and NADPH However, more ATP needs to be consumed than NADPH for one round of the Calvin cycle Plants need a method to increase ATP production without affecting the production of NADPH o Solution: cyclic electron flow LIGHT-INDEPENDENT REACTIONS CALVIN CYCLE – How the Calvin Cycle produces carbohydrates Cyclical process with 3 phases o Carbon fixation – incorporation of CO2 o Reduction – utilization of energy molecules to form organic compound o Regeneration – regenerates molecules for another cycle 6 cycles needs to occur simultaneously to form a single glucose molecule 61  SBI4U1 – 2024 PHASE 1: CARBON FIXATION CO2 (1C) reacts with a molecule known as ribulose-1, 5-bisphosphate (RuBP) (5C) to form a short-lived 6C intermediate Each intermediate 6C molecule is immediately split into two 3- phosphoglycerates (3PG) Since this occurs 6 times… o 6 CO2 + 6 RuBP = 6 short-lived 6C intermediate = 12 3PG Rubisco – Large, slow reacting enzyme Purpose is to catalyze the first reaction of fixing the CO2 to RuBP Makes up for half the proteins in a leaf o Most abundant protein on Earth PHASE 2: REDUCTION 1. ATP phosphorylates each 3-phosphoglycerates (3PG) to form 1,3-bisphosphoglycerate 2. NADPH is oxidized while reducing 1,3- bisphosphgoglycerate to form glyceraldehyde-3- phosphate (G3P) PHASE 3: REGENERATION 12 G3Ps will be formed by the end of phase 2 o Remember that 6 cycles are occurring simultaneously 2 G3P will exit the cycle and will eventually become glucose or other types of organic compounds o 2 3-carbon molecules of G3P combine to form a single 6-carbon glucose molecule The other 10 G3P will continue in the cycle to help regenerate the starting substances 62 SBI4U1 – 2024 CALVIN CYCLE: REGENERATING MOLECULES The 10 G3P that continue through the cycle will be synthesized into RuBP 10 x 3C (G3P) → 30C / 5C (RuBP) -> 6 RuBP o Each G3P consist of 3 carbons; 10 G3Ps gives a total of 30 carbon atoms o Each RuBP molecule requires 5 carbons; 30 carbons helps to regenerate the original 6 RuBP molecules initially used We have successfully regenerated each of the RuBPs that were initially used **WATCH** Nature’s smallest factory: The Calvin Cycle (~6 min) 63 SBI4U1 – 2024 HOMEWORK: TEXTBOOK Complete the following questions from Chapter 5.2 on page 228 of your textbook: #8, 10. 8. Careful measurements indicate that the Calvin cycle in a plant leaf is occurring very slowly. In such a situation, there is a reduced demand for both NADPH and ATP. a) What benefit (if any) would the light-dependent reactions still have for this plant? b) Can you think of any environmental conditions under which such a situation might arise? 10. Rubisco is the world’s most abundant protein, yet it is not found inside any animal cells. Suggest a reason why animals do not need or use this protein. Complete the following questions from Chapter 5 on page 247 of your textbook: #47. 47. The term “dark reactions” was once used to describe the Calvin cycle. Use your current knowledge to suggest a possible reason why this term is no longer used. 64 SBI4U1 – 2024 10. ALTERATIVE MECHANISMS – C4 & CAM PLANT ADAPTATIONS C3 PLANTS Plants whose first organic product of carbon fixation is a 3-carbon compound CO2 + RuBP -> 3PG (3-Phosphoglycerate) C3 plants undergo photosynthesis as described STOMATA Small pores found on the leaf’s surface Allow plants to control the exchange of gas with the atmosphere o Surrounded by guard cells that allows the plants to close its stomata CO2 and O2 move in and out of the plants through these Stomata are opened during the day and closed at night C3 PLANT LIMITATIONS In hot, arid conditions, plants close the stomata to prevent water loss How might this affect CO2 and O2 concentrations? Effects of close stomata on gases: o CO2 decreases o O2 increases Effects on processes: o No changes to light reactions o Calvin Cycle starts to slow down and may eventually completely stop o No glucose production Rubisco: o May bind to both O2 or CO2 o Increase [O2] means rubisco will bind to O2 instead of CO2 65 SBI4U1 – 2024 PHOTORESPIRATION Photorespiration – the catalysis of O2 instead of CO2 by rubisco into RuBP, which slows the Calvin cycle, consumes ATP, and results in a release of carbon Similar to ‘normal’ photosynthesis except O2 is consumed by rubisco instead of CO2 Produces no organic fuel Wastes energy and reducing power (NADPH) Results in the production of dangerous reactive oxygen species such as H2O2 (hydrogen peroxide) in the plants Many terrestrial plants, especially those living in hot, dry climates, face the problems of photorespiration and water loss. o They struggle to exchange gases with the atmosphere without suffering excessive water loss o These plants have evolved a variety of adaptations in response to the harsh conditions PHOTOSYNTHETIC ADAPTATIONS Two other plant types have adapted photosynthesis to dry, arid conditions: C4 plants – evolved structural separation CAM plants – evolved temporal behavioural separation C4 PLANTS C4 PLANTS: LEAF STRUCTURE Difference between C3 and C4 leaf structure: C4 plants have specialized cells known as bundle-sheath cells that tightly pack next to mesophyll cells and around vascular tissue (veins) bundles 66 SBI4U1 – 2024 C4 PLANT ADAPTATION The processes of photosynthesis has been compartmentalized Light reaction that produces O2 occurs in the mesophyll cells Calvin cycle occurs in the bundle-sheath cells (isolated from O2) How does CO2 get into the bundle-sheath cells? Use an enzyme that has a very affinity for CO2 over O2 Phosphoenolpyruvate (PEP) carboxylase will bind a CO2 to a phosphoenolpyruvate (PEP) molecule Enzyme has such a strong affinity for CO2 that it will still fix carbon to PEP even when O2 levels are much higher C4 PLANT ADAPTATION: STEP 1 CO2 is added to phosphoenolpyruvate (PEP) to form a 4-carbon molecule oxaloacetate This is our first carbon fixation step and a 4C molecule is formed, hence why these are known as C4 plants Oxaloacetate will undergo a reaction and form malate C4 PLANT ADAPTATION: STEP 2 Malate is transported into the bundle-sheath cells where it is broken down into CO2 and pyruvate CO2 proceeds into the Calvin cycle as it would in C3 plants Pyruvate will return to the mesophyll cells where it will convert back into PEP 67 SBI4U1 – 2024 Mesophyll cells acts as CO2 pump Keeps concentration of CO2 in bundle-sheath cells high so that rubisco will be more likely bind to it Note that to convert pyruvate back to PEP requires ATP This adaptation costs energy for it to proceed CAM PLANTS Crassulacean Acid Metabolism Succulent (water-storing) plants CAM PLANT ADAPTATION Daytime: Stomata closed Conserve water No CO2 uptake Light reaction still occurs Still producing ATP, NADPH, and O2 Decreased [CO2] and increased [O2] would usually result in halting Calvin cycle but CAM plants have an adaptation for this 68 SBI4U1 – 2024 Nighttime: Cooler Stomata open CO2 enter Enzyme PEP carboxylase binds CO2 to PEP to form oxaloacetate which will convert into malate The malate produced during this nighttime process is stored in the plant’s vacuoles of mesophyll cells Daytime: Malate is broken down to CO2 and pyruvate CO2 will then proceed to the Calvin cycle Pyruvate will be converted back into PEP to be used again during the night process C4 AND CAM PLANTS CO2 is incorporated into organic intermediates which is then released into the Calvin cycle generating an environment that is high in CO2 so that Rubisco does not bind to O2 C4 plants – initial carbon is fixed in a separate compartment CAM plants – Initial carbon is fixed at a separate time of the day 69 SBI4U1 – 2024 HOMEWORK: ALTERNATE MECHANISMS OF CARBON FIXATION 1. a) Define photorespiration. b) What gas can compete with CO2 for the binding site of the enzyme rubisco? c) Under normal conditions, what proportion of fixed carbon is affected by photorespiration in C3 plants? d) Compare the end products of photosynthesis and photorespiration. 2. How does temperature affect the relative amounts of photosynthesis and photorespiration that occur in C3 plants? 3. a) Label A, B, C, D, and E in the diagram. 70 SBI4U1 – 2024 b) What type of cell-cell connection do malate and pyruvate go through to move from one cell into the other? 4. a) At what time of day would you expect to find the most malate in CAM plants? b) When would you find the least amount of malate in CAM plants? c) Why do plants that use CAM photosynthetic pathways close their stomata during the day? d) During the cool of evening, CAM plants open their stomata. What gas is preferentially absorbed at this time? e) Explain how this gas is stored for daytime use. 71 SBI4U1 – 2024 11. COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION Aerobic cellular respiration and photosynthesis – two main chemical processes essential to most of the life on Earth o Complete a cycle of energy transformation in living things Below is an image (Figure 2 from textbook – page 238) that compares cellular respiration in the mitochondria and photosynthesis in the chloroplast. 72 SBI4U1 – 2024 COMPARISON OF PLANT AND ANIMAL DEMANDS FOR ENERGY AND MATERIALS Plants Animals Primary energy source Light Food Method of obtaining primary Consumption of other living Photosynthesis energy source organisms Carbohydrates and other energy-rich molecules, such as fats and Energy storage lipids Immediate source of free ATP energy Primary source of ATP Aerobic cellular respiration Primary organic materials for growth, reproduction, and Carbohydrates, lipids, proteins, and nucleic acids repair Source of carbon in organic Carbon fixation during Consumption of other living materials photosynthesis organisms 73 SBI4U1 – 2024 HOMEWORK: PHOTOSYNTHESIS & COMPARISON REVIEW QUESTIONS 74 SBI4U1 – 2024 75 SBI4U1 – 2024 HOMEWORK: COMPARING CELLULAR RESPIRATION AND PHOTOSYNTHESIS 76 SBI4U1 – 2024 77