General Biology 1 Past Paper Quarter 2 Module 3 & 4 - Photosynthesis PDF

General Biology 1 Quarter 2 – Module 3 and 4: Photosynthesis What I Need to Know This module was designed and written with you in mind. It is here to help you master Photosynthesis. The scope of this module permits it to be used in many differe...

General Biology 1 Quarter 2 – Module 3 and 4: Photosynthesis What I Need to Know This module was designed and written with you in mind. It is here to help you master Photosynthesis. The scope of this module permits it to be used in many different learning situations. The language used recognizes the diverse vocabulary level of students. The lessons are arranged to follow the standard sequence of the course. But the order in which you read them can be changed to correspond with the textbook you are now using. The module has: Lesson 1 – Light reactions Lesson 2 – Calvin cycle After going through this module, you are expected to: a. Describe the patterns of electron flow through light reaction events (STEM_BIO11/12-IIa-j-4) b. Describe the significant events of the Calvin cycle (STEM_BIO11/12-IIa-j-5) What I Know Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper. 1. What are the end products of light reactions? a. Glucose b. Carbon Dioxide c. NADPH and ATP d. Water 2. For the capture of light energy, the associated region of the chloroplast is a. Thylakoid membrane b. Outer membrane c. Stroma d. Both a and b 3. How many Photosystem/s do plants have? a. 1 b. 2 c. 3 d. Photosystems are as many as there are leaves 4. What colors of light are most effective for photosynthesis? a. Red, blue, violet b. Green, yellow, orange c. Green, red, blue d. All colors of light are equally effective 5. Most plants appear green because the chlorophyll a. Absorbs green light b. Does not absorb green light c. Absorbs violet light d. Does not absorb violet light 6. Carbon fixation reaction converts a. Inorganic carbon into organic acid. b. CO2 into glucose. b. Inactive rubisco into active rubisco. d. An organic acid into CO2. 7. C4 plants fix carbon by a. Incorporating CO2 into oxaloacetate, followed by conversion to malate. b. Incorporating CO2 into citrate via reverse glycolysis. c. Incorporating CO2 into glucose via the Krebs cycle. d. The same pathway as C3 plants, however, the product is modified. 8. Which of the following does not occur during Calvin cycle? a. Oxygen release b. Carbon fixation c. NADPH oxidation d. Regeneration of the CO2 acceptor 9. Which of the following statements describes carbon fixation correctly? a. Use of RuBisCO to form 3-PGA b. Incorporation of CO2 into organic compound c. Formation of RuBP from molecules of G3P d. Production of carbohydrates from G3P 10. Which of the following molecules needs to enter the Calvin cycle continuously for the light-independent reactions to take place? a. RuBisCO b. 3-PGA c. CO2 d. RuBP Lesson 1 Light Reactions The energy being utilized by most living organisms come from the sun. This energy in the form of radiant energy is harnessed by photosynthetic organisms (plants, algae, and bacteria) through a 3-stage process known as photosynthesis. The 3-stage process consists of 1) capturing light energy from the sunlight, 2) utilizing the harnessed radiant energy to produce ATP, and producing NADPH from NADP+, and 3) using the ATP and NADPH produced as fuel in synthesizing glucose from CO2. What’s In Observe the chemical equation of photosynthesis below and briefly explain how this process is related/connected to the ATP-ADP cycle. _______________________________________________________________________________________________ _______________________________________________________________________________________________ What’s New Answer the questions based on what can be observed in the image that follows. Write your answers on a separate sheet of paper.  1. On which organelle does photosynthesis take place? _________________. 2. Photosynthesis involves light reactions and light independent reaction. The light- independent reaction is a cycle also known as ______________. 3. On which part of the chloroplast do light reactions take place? _______________. 4. Based on what can be observed from the image, what is the purpose of light reactions in photosynthesis? ____________________________________________________ 5. Which color/s of light do the thylakoids absorb? Which color/s do they reflect?_________________________________________________________ _____________________________________________________________________ 7 completely identical plants (identical genes, etc.) had been exposed to 7 different colors (red, orange, yellow, green, blue, indigo, violet) of light (1 plant for each color) over 1 year. None of the plants had been exposed to a different color of light during the said time. After a year, 6 plants had grown, although not at the same rates, while one plant had long since died. Which among the 7 plants had died? Provide a brief explanation of your answer. ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ What is It Light energy initiates photosynthesis when specialized pigments absorb the energy in light. Plants in general contain two kinds of photosynthetic pigments: Chlorophyll A and Chlorophyll B. The first 2 stages in photosynthesis are known as the light-dependent reactions or light reactions. The light reactions are divided into 4 stages: 1. Primary photoevent - In this stage, a photon of light is captured by a pigment, causing excitation of an electron within that pigment. 2e 2. Charge separation – The energy that caused the excitation of an electron is then transferred to a reaction center which transfers an excited electron to an electron acceptor, initiating the next stage. 3. Electron transport – The excited electrons are transferred along with a series of electron carriers embedded in a photosynthetic membrane and are eventually transferred to a final electron acceptor (NADP ) reducing it to + NADPH. As the electrons are shuttled along with these carriers, they generate a proton gradient which makes way for the last stage 4. Chemiosmosis – The protons that have accumulated on one side of the membrane due to the previous stage will flow back across the membrane via ATP synthase where ATP is produced through chemiosmotic synthesis.  In chloroplasts, light is captured by photosystems which consist of 2 closely linked components: Antenna Complex – Light- harvesting complex (circle) consisting of 2e hundreds of pigment molecules that gather photons and transfer the captured light energy to the reaction center. In chloroplasts, the complex consists of chlorophyll molecules that are linked together and bound tightly by proteins. The resulting energy from the absorption of a photon passes from one pigment to another until it reaches the reaction center. Note that it is the energy that is passed on and not the excited electrons themselves. Reaction Center – A transmembrane protein-pigment complex (pentagon) that releases an excited electron out of the photosystem. Note that it is not just the energy that is released, but the excited electron as well, as opposed to the antenna complex. In plants’ chloroplasts, water is split through oxidation releasing oxygen as well as 2 protons (H+) and the two electrons replace the released electrons. Plants utilize 2 photosystems (Photosystem II and Photosystem I) in a series known as non-cyclic phosphorylation to produce ATP as well as NADPH. The term “non-cyclic” describes the path of the electrons that are ejected from the photosystems where they end up in NADPH instead of returning to the photosystems. The electrons lost in Photosystem II will then be replaced/replenished by the splitting of water (H2O) molecules. The reaction center of Photosystem II possesses an absorption peak of 680 nm giving it the name P680. This photosystem generates enough oxidizing power to oxidize (take away electron/s from) water. Photosystem I on the other hand can absorb up to 700 nm (peak absorption) which therefore gives its reaction center pigment the name P700. Between the two photosystems is cytochromeb6-f complex, a complex of electron carriers connecting the photosystems which, while serving as electron carriers, generates a proton gradient across the thylakoid membrane. The reaction begins when the antenna complex of photosystem II absorbs 2 photons, it passes the light energy around until it reaches the reaction center pigment P680 where a pair of electrons are ejected due to excitation. The pair of electrons exiting from photosystem II then reduces a quinone molecule, the primary acceptor of Photosystem II, and turns it into plastoquinone, a strong electron donor that brings the electrons to the b6-f complex, a proton pump embedded in the thylakoid membrane. The pair of electrons causes the complex to pump protons across the membrane before being carried by another carrier molecule (plastocyanin) to photosystem I where they will be used to replenish the reaction center P700. The antenna complex in photosystem I will also absorb 2 photons and pass the light energy to the reaction center P700 which will eject 2 electrons. This pair of electrons however is not received by a quinone molecule, and instead accepted by 2 iron-sulfur protein molecules known as ferredoxin (one electron per ferredoxin molecule), carrier molecules that will donate the electrons to NADP+ reducing it to NADPH in a process catalyzed by an enzyme (NADP reductase). The transport of electrons through the b6-f complex and the reduction of NADP+ to NADPH both contribute to generating a proton gradient which the plants take advantage of to produce ATP molecules via chemiosmosis of Hydrogen ions (H+) through the enzyme ATP Synthase, an enzyme that produces ATP by acting as a channel for protons across the thylakoid membrane. The entire reaction occurs twice, producing one molecule of O2, 3 molecules of ATP, and 2 molecules of NADPH, after 8 photons (4 from each photosystem) are absorbed. The 4 electrons from water end up replacing the 4 electrons ejected from photosystem II. The 4 electrons that came from photosystem II replaced the 4 electrons that photosystem I ejected. The 4 electrons from photosystem I end up in the 2 NADPH molecules. What’s More Activity Complete the flowchart by arranging the light reaction processes in chronological order. Choose your answers from the tables provided on the next page.  Photosystem II a. Plastocyanin carries b. Plastoquinone c. Energy from light is the electrons to passes the electrons passed to P680 photosystem I to b6-f complex d. Antenna complex e. b6-f complex f. Water is split to absorbs 2 photons generates a proton replenish the lost gradient electrons in P680 g. Reaction center h. 2 electrons reduce 1 i. Proton gradient ejects 2 electrons quinone molecule powers ATP synthesis Photosystem I a. Reaction center b. Reduced Ferredoxin c. Antenna complex ejects 2 electrons molecules pass 2ē to absorbs 2 photons NADP + d. NADP is reduced to e. Energy from light is f. 2 electrons reduce 2 + NADPH passed to P700 ferredoxin molecules What I Have Learned Fill in the blanks. Complete the sentences by providing the missing words. Write your answers on a separate sheet of paper. 1. The antenna complex is a __________________ complex that gathers photons and transfers the captured light energy to the ________________. 2. The ________________ is a proton pump embedded in the thylakoid. 3. Plants utilize photosystems II and I in a series know as _____________ phosphorylation. 4. The product of photosystems II and I are ____________ and ____________. 5. The energy utilized by most living organism comes from the __________. 6. The primary acceptor of electrons from photosystem II is a _____________ molecule. 7. ______________ carries 2 electrons to photosystem I. 8. The transport of electron through the __________________ and reduction of NADP+ to NADPH both generate a ____________ gradient. 9. In plants’ chloroplasts, ___________ is split releasing _____________ and 2 _____________ and 2 electrons replace the released electrons. 10. The entire reaction occurs _________, producing ______ molecule/s of O2, 3 molecules of ________ and ________ molecule/s of NADPH. What I Can Do Activity Read and ponder on the questions below then provide an answer based on what you’ve learned in the previous lesson. What will happen if a plant that reflects green light evolves to become capable of absorbing it along with the other colors (wavelengths) of visible light? (Hint: How will this affect the color of the plant’s leaves? Its growth rate? Excluding all other factors except light, can the plant thrive/flourish in the different regions (Tropical, temperate, polar) of the world?) Explain. _______________________________________________________________________________________ _______________________________________________________________________________________ Rubric Points Correctly explains how leaves will turn black in terms of color 5 absorption Correctly explains how the increase in absorption range will benefit 5 the production of ATP and NADPH which can possibly increase growth rate Explains the possibility of a plant surviving in different regions of 5 the world due to the wide range of wavelength of light it can absorb What will happen if a semi-transparent screen that only allows green light to pass through suddenly envelopes the entire planet? (Hint: How will this affect plants? Will all plants die/survive?) Explain. _______________________________________________________________________________________ _______________________________________________________________________________________ Rubric Points Correctly explains how leaves remain green due to reflecting green 5 light Correctly explains how plants that rely on blue and red light will die 5 due to absence of said colors since they are blocked from entering atmosphere Explains the possibility of survival and extinction of plants in terms 5 of adaptation Assessment Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper. 1. Which of the following correctly represents the flow of electrons during light reactions? a. H2O > Photosystem I > Photosystem II b. H2O > Photosystem II > Photosystem I c. H2O > NADPH > ATP d. H2O > ATP > NADPH 2. Which of the following is not a component of a photosystem? a. Reaction Center b. Antenna Complex c. Both a and b d. None of the above 3. Where do the electrons in the light reactions come from? a. H2O b. Photosystem I c. Photosystem II d. Both b and c 4. How is a reaction center pigment different from an antenna complex pigment? a. The reaction center pigment loses electrons when light energy is absorbed b. The antenna complex pigment loses electrons when light energy is absorbed c. The reaction center pigment does not lose electrons d. The antenna complex pigment loses 2 electrons 5. How many photons does it take to reduce NADP+ to NADPH? a. 1 b. 2 c. 4 d. 8 Additional Activities Illustrate the path of electrons throughout the light reactions starting from 2 molecules of water and ending in 2 molecules of NADPH. Answer Key 15. d 14. b ATP; 2 What’s New 13. f Twice; 1; 10. 1. Chloroplast 12. a protons 2. Calvin Cycle 11. e oxygen; 3. Thylakoids 10. c Water; 9. 9. i 4. Energy proton D 5. B 5. 8. a source to complex; A 4. A 4. 7. e b6-f 8. A 3. B 3. excite 6. b n electrons C 2. A 2. 5. h Plastocyani 7. 5. All visible B 1. C 1. 4. f Quinone 6. Assessment What I Know colors. Green 3. g Sun 5. 2. c ATP 1. d NADPH; 4. More Non-cyclic 3. What’s b6-f complex 2. center reaction harvesting; Light 1. learned What I have  Lesson 2 Calvin Cycle Photosynthesis consists of a three-stage process which are: 1) capturing light energy from the sunlight, 2) utilizing the harnessed radiant energy to produce ATP, and producing NADPH from NADP+, and 3) using the NADPH and ATP produced as fuel in synthesizing glucose from CO2. The third stage is also known as the light-independent reactions since the series of reactions involved in this stage may occur either in the presence or absence of light as long as ATP and NADPH are available. What’s In Read and ponder on the question below and provide an answer based on the knowledge acquired in the previous lesson. Write your answer on a separate sheet of paper. How would a mutation in plants that makes the thylakoid membrane permeable to charged ions affect the Calvin cycle? (Hint: Will there be fewer or more carbohydrates produced? Will there be no effect on the Calvin cycle? Explain) _______________________________________________________________________________________ _______________________________________________________________________________________ Construct a diagram that connects the complete diagram of light reactions to the complete diagram of the Calvin cycle. What’s New Answer the questions below based on what you can observe on the image that follows. Calvin Cycle 1. 5-carbon molecule where carbon from CO2 attaches during carbon fixation ________________________ 2. Due to it being too energetically unstable, the short-lived intermediate quickly splits into two molecules of _________________________ 3. 12 phosphate groups are added to 12 molecules of 3-Phosphoglycerate and produces 12 molecules of ______________ 4. How many G3P molecule/s is/are harnessed to produce 1 glucose molecule? 5. How many G3P molecules are recycled into RuBP?  What is It The Calvin cycle is divided into 3 phases: carbon fixation, reduction, and regeneration. 1. Carbon Fixation At the very start of this cycle, inorganic carbon that is in CO2 attaches to an organic 5-carbon molecule known as ribulose, 1,5-biphosphate (RuBP) via carbon fixation, a process carried out by rubisco (enzyme) or (ribulose bisphosphate carboxylase/oxygenase). The product resulting from carbon fixation is an energetically unstable 6- carbon molecule. This molecule splits into two 3-Phosphoglycerate (PGA) molecules. Since the first intermediate molecule formed is a 3-carbon molecule, this cycle is also known as the C3 cycle. 6  2. Reduction The molecules of 3-Phosphoglycerate (PGA) each receive a phosphate group from ATP and turns into 1,3-biphosphoglycerate. 2 electrons (for every NADPH molecule) are then donated to each of the new intermediates, reducing them to glyceraldehyde 3-phosphate (G3P). 3. Regeneration of rubisco 7 Within 6 full cycles, 6 molecules of CO2 attach to 6 RuBP molecules, producing 12 molecules of PGA which will be reduced to 12 G3P Molecules, 2 of which will be harnessed by plants to produce glucose, and the remaining 10 will regenerate the consumed 6 molecules of RuBP by spending another 6 ATP molecules. For a net gain of two G3P molecules, the cycle consumes a total of 18 ATP molecules and 12 NADPH molecules. Light reactions will replenish NADPH and ATP while the G3P molecules will be used for the synthesis of organic compounds such as glucose, sucrose, and other carbohydrate molecules.  18 ATP 2 G3P 12 NADPH The enzyme rubisco has another enzymatic activity that competes with carbon fixation. In a 9 process called photorespiration, rubisco oxidizes the RuBP molecule, O2 attaches to RuBP and releasing CO2 and therefore essentially reversing carbon fixation. During hot, arid conditions, plants close their stomata to prevent excessive water loss, however, as a result, plants cannot take in CO2, and O2 from light reactions will continue accumulating. The loss for the total yield of the Calvin cycle can rise to 50%, a loss that is far from trivial. To combat this, some plants fix CO2 to phosphoenolpyruvate (PEP) in a process catalyzed by the enzyme PEP carboxylase. The resulting 4- carbon molecule known as oxaloacetate is then converted into malate, a different 4-carbon molecule that moves to the bundle-sheath cells where it is decarboxylated into pyruvate and CO2. Since the first intermediate molecule produced is a 4-carbon molecule (1 carbon from CO2 and 3 from PEP), this pathway is known as the C4 pathway. The CO2 from the C4 pathway then proceeds to enter the C3 pathway and go through the Calvin cycle. C4 plants, therefore, perform both C3 and C4 pathways to minimize the effects of photorespiration. 10  In another group of plants, the Crassulacean Acid Metabolism (CAM) plants, both C3 and C4 pathways are utilized. However, unlike C4 plants where the two pathways occur in different cells (C4 occurs in a mesophyll cell and C3 occurs in an adjacent bundle-sheath cell), CAM plants utilize both pathways in the same cell. Also, CAM plants adopt another strategy to minimize photorespiration. The stomata of CAM plants are open during nighttime to capture CO2 via the C4 pathway and close during daytime. Carbon fixation products are stored and then decarboxylated at daytime to drive Calvin cycle. This adaptation not only minimizes photorespiration, but it also lessens water lost due to transpiration. Both CAM and C4 adaptations incorporate CO2 into organic compounds before injecting carbon dioxide into Calvin cycle. The main difference in the two adaptations is that the C4 pathway spatially separates the first step in carbon fixation from Calvin cycle whereas CAM separates the time in which these reactions occur. C4 C3 CAM What’s More Activity Complete the flowchart by filling in the missing intermediate molecules. Write your answers on a separate sheet of paper. What I Have Learned 1. The Calvin cycle is divided into 3 ________________: __________________, __________________ and __________________. 2. The inorganic carbon from CO2 attaches to an organic 5-carbon molecule known as _________________________________. 3. Carbon fixation of inorganic carbon from CO2 to RuBP is carried out by the enzyme ____________________________________. 4. The first intermediate molecule of C3 pathway is ______________________. 5. The first intermediate molecule of C4 pathway is _____________________. 6. The molecules of 3-Phosphoglycerate (PGA) each receive a ____________ from _______ and turns into _____________________. 7. For a net gain of ___ G3P molecules, the cycle consumes a total of ___ _______________ molecules, and ___ _____________ molecules. 8. In C4 plants, C3 occurs in _____________ and C4 occurs in ______________. 9. CAM Plants _______ their stomata at daytime. CAM plants’ adaptation not only minimizes photorespiration, it also _______________________________________________________________________________________________ ______________________________________________________________________________________________. What I Can Do Activity Read and ponder on the questions below then provide an answer based on what you have learned in the previous lesson. Write your answers on a separate sheet of paper. What will happen if a plant undergoes a mutation wherein its thylakoid membrane becomes permeable to charged ion? What effect will it have on the dark reactions of the plant? Explain. _______________________________________________________________________________________ _________________________________________________________ Assessment Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper. 1. How does Photorespiration affect the Calvin cycle? a. Reverses carbon fixation b. Speeds up carbon fixation c. Both a and b d. None of the above 2. Why does the short-lived intermediate after C3 carbon fixation quickly separate into 2 PGA molecules? a. It’s the intermediate’s natural tendency b. It’s energetically unstable c. Both a and b d. There is no short-lived intermediate for the C3 pathway 3. What molecule is produced when CO2 attaches to PEP? a. Malate b. Oxaloacetate c. Pyruvate d. RuBP 4. Where does the Calvin cycle occur in C4 plants? a. Mesophyll Cell b. Stomata c. Bundle sheath cell d. None of the above 5. Which order of molecular conversions is correct for the Calvin cycle? a. RuBP + G3P → 3-PGA → sugar b. RuBisCO → CO2 → RuBP → G3P c. RuBP + CO2 → [RuBisCO] 3-PGA → G3P d. CO2 → 3-PGA → RuBP → G3P Additional Activities Read and ponder on the question below and provide an answer in essay format. Write your answer on a separate sheet of paper. Based on the study, tropical forests are responsible for 34% of photosynthesis happening on land. However, despite the large consumption of CO2 during photosynthesis, there is little to no net contribution to reducing global warming. Why? List down 2 reasons and explain.  Education. Raven, P., Johnson, G., Mason, K., Losos, J., & Singer, S. (2017). Biology. McGraw-Hill Jackson, R. B. (2013). Campbell Biology 10th Edition. US: Pearson Education. Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & References What I Know Assessment What I have learned 1. A 1. A 1. Phases: carbon fixation, reduction, 2. A 2. B regeneration of RuBP 3. A 3. B 2. Ribulose 1,5-Biphosphate 4. B 4. C 3. Ribulose Biphosphate 5. C 5. C Carbxylasae/Oxygenase (Rubisco) 4. 3-Phosphoglycerate 5. Oxaloacetate 6. Phosphate group; ATP; 1,3- biphosphoglycerate 7. 2; 18 ATP; 12 NADPH 8. Mesophyll cell; bundle-sheath cell 9. Opens 10. Reduces water loss from transtranspiration What’s More What’s New 1. Short-lived intermediate 1. Ribulose Biphosphate 2. 3-Phosphoglycerate 2. 3-Phosphoglycerate 3. 1,3-Biphosphoglycerate 3. 1,3-Biphosphoglycerate 4. Glyceraldehyde 3-Phosphate 4. 2 5. Oxaloacetate 5. 10 6. Malate 7. Pyruvate 8. Ribulose 1,5-Biphosphate 9. CO2 10. Short-lived intermediate 11. 3-Phosphoglycerate 12. 1,3-Biphosphoglycerate 13. Glyceraldehyde 3-Phosphate Answer Key