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Questions and Answers
What is the main function of photosynthesis in plants?
Which process involves the breaking of chemical bonds to release energy?
How are oxidation and reduction reactions related in metabolic processes?
What role do enzymes play in metabolism?
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What do plants provide for animals through the photosynthesis process?
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What is the final electron acceptor in aerobic respiration?
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Which of the following processes occurs in the absence of oxygen?
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What is produced as a by-product of aerobic respiration?
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How many ATP molecules are gained from glycolysis?
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What type of fermentation produces ethyl alcohol?
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In which location does the Krebs cycle take place?
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Which of the following statements about aerobic respiration is true?
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What impact does a rise in air temperature from 20C to 30C have on respiration rates?
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What is the result of low water levels in plants?
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What occurs if oxygen is not available after glycolysis?
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How many carbon dioxide molecules are released during one cycle of the citric acid cycle?
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What acts as the ultimate electron acceptor in the electron transport system?
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What is produced when high-energy electrons and hydrogen are removed during the Krebs cycle?
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What drives the formation of ATP during chemiosmosis?
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What is the net gain of ATP molecules produced through cellular respiration?
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What is a consequence if light intensity is too high during photosynthesis?
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How does carbon dioxide reach the chloroplasts in mesophyll cells?
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What effect does deforestation and fossil fuel use have on carbon dioxide levels?
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What is one function of water in the process of photosynthesis?
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Which factor can limit the rates of photosynthesis apart from light intensity?
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What is the role of chlorophyll b in photosynthesis?
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In which part of the chloroplast do the light-independent reactions occur?
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What is one main product of the light-dependent reactions of photosynthesis?
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Which of the following pigments is responsible for the yellow and orange colors in plants?
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What molecule combines with carbon dioxide during the Calvin cycle?
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What is the primary function of pigments in photosynthesis?
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What happens to electrons when chlorophyll absorbs light energy?
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Which photosystem is responsible for water-splitting and photolysis?
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What is produced as a by-product during photolysis in photosynthesis?
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Which molecule is the primary electron acceptor for Photosystem I?
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How is ATP formed during the process of photosynthesis?
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What role do antenna pigments play in photosystems?
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Which process describes the movement of protons across the thylakoid membrane?
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Which part of the chlorophyll molecule is responsible for capturing light energy?
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How does electron flow between photosystem II and I contribute to photosynthesis?
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Study Notes
Introduction to Plant Metabolism
- Metabolism is the sum of all biochemical processes in living organisms
- Photosynthesis converts light energy into a usable form
- Respiration releases stored energy
- Animals rely on green plants for food, oxygen, shelter, and other products
Enzymes and Energy Transfer
- Enzymes regulate anabolism and catabolism
- Anabolism forms chemical bonds to build molecules
- Catabolism breaks chemical bonds
- Oxidation is the loss of electrons
- Reduction is the gain of electrons
- Oxidation-reduction reactions involve the transfer of energy and occur in pairs
- Hydrogen is lost during oxidation and gained during reduction
- Oxygen is usually the final electron acceptor
Respiration - The Essence of Respiration
- Respiration releases energy from glucose
- Initiated in the cytoplasm and completed in the mitochondria
- Requires oxygen
- C6H12O6 + 6O2→ 6CO2 + 6H2O + energy
Respiration - Anaerobic Respiration and Fermentation
- Occurs in the absence of O2
- Releases less energy than aerobic respiration
- Alcohol fermentation: C6H12O6→ 2C2H5OH + 2CO2 + ATP
- Lactic acid fermentation: C6H12O6→ 2C3H6O3 + ATP
Respiration - Introduction to the Major Steps of Respiration
-
Glycolysis (first stage)
- Glucose is converted to a fructose molecule in the cytoplasm
- Fructose is converted to GA3P (glyceraldehyde 3-phosphate)
- Energy, H, and water are removed to yield pyruvic acid
- Energy and H are picked up by NAD
- 2 ATP molecules are gained
- No O2 is required
- Either aerobic respiration, true anaerobic respiration, or fermentation may occur next
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Citric Acid (Krebs) cycle (second stage)
- Occurs in the fluid matrix of cristae in mitochondria
- High energy electrons and hydrogen are removed as the cycle proceeds
- NADH, FADH2, and a small amount of ATP are produced
- CO2 is produced as a by-product
-
Electron Transport (third stage)
- Occurs in the inner membrane of mitochondria
- NADH and FADH2 donate electrons to the electron transport system
- Produces ATP, CO2, and water
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Anaerobic Respiration and Fermentation
- If there is insufficient oxygen to complete aerobic respiration after glycolysis, the H released during glycolysis may be transferred back to create ethyl alcohol or lactic acid
- True anaerobic respiration involves combining H with an inorganic ion
- Oxygen is not required
- Glycolysis + fermentation yields 2 ATP from glycolysis
- Glycolysis + aerobic respiration should yield 36 ATP
- Fermentation equations:
Respiration - Factors Affecting the Rate of Respiration
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Temperature
- Respiration rates double or triple when air temperature rises from 20C to 30C
-
Water
- Low water levels decrease respiration
- Water acts as a medium for enzymatic reactions
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Oxygen
- Flooding can reduce the oxygen supply to roots, which can reduce respiration and be fatal to plants
- Crops can be stored in low oxygen conditions to minimize respiration
Respiration - A Closer Look at Respiration
-
Glycolysis Reexamined
- Steps:
- Phosphorylation: glucose is converted to a fructose molecule that carries two phosphates
- Sugar Cleavage: fructose is split into two 3-carbon fragments: GA3P (glyceraldehyde 3-phosphate)
- Pyruvic acid formation: hydrogen, energy, and water are removed, leaving pyruvic acid
- Prior to entering the citric acid cycle, pyruvic acid loses CO2 and is converted to acetyl CoA
- If O2 is not available, anaerobic respiration or fermentation occurs
- Hydrogen released during glycolysis is transferred back to pyruvic acid, creating ethyl alcohol or lactic acid
- Steps:
-
Transition Step to the Citric Acid (Krebs) Cycle
- After glycolysis, a molecule of CO2 is removed from pyruvate, and NADH is produced
- The 2-carbon fragment combines with coenzyme A to form acetyl CoA
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The Citric Acid (Krebs) Cycle Reexamined
- Acetyl CoA first combines with oxaloacetic acid, producing citric acid.
- Each cycle uses 2 acetyl CoA, releases 3 CO2, and regenerates oxaloacetic acid
- O.A.+ acetyl CoA + ADP+P+3NAD + FAD → O.A.+ CoA + ATP + 3NADH + H+ + FADH2+ 2CO2
- High energy electrons and hydrogen are removed, producing NADH, FADH2, and ATP
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Electron transport and Oxidative Phosphorylation
- Energy from NADH and FADH2 is released as hydrogen and electrons are passed along the electron transport system.
- Protons build up outside the mitochondrial matrix, establishing an electrochemical gradient
- Chemiosmosis couples the transport of protons into the matrix with oxidative phosphorylation: the formation of ATP
- Oxygen acts as the ultimate electron acceptor, producing water as it combines with hydrogen
- Produces a net gain of 36 ATP, 6 molecules of CO2, and water
Additional Metabolic Pathways
- Other processes contribute to plant growth, development, reproduction, and survival.
- Compounds produced include: sugar phosphates, nucleotides, nucleic acids, amino acids, proteins, chlorophylls, cytochromes, carotenoids, fatty acids, oils, and waxes
- Secondary metabolism consists of metabolic processes not required for normal growth and development
- Enable plants to survive and persist under special conditions
- Colors, aromas, poisons give plants a competitive edge
- Examples: codeine, nicotine, lignin, salicin, camphor, menthol, rubber
Assimilation and Digestion
- Assimilation - The conversion of organic matter produced in photosynthesis to build protoplasm and cell walls
- Sugars are transformed into lipids, proteins, or other carbohydrates (sucrose, starch, and cellulose)
- Digestion - The conversion of starch and other insoluble carbohydrates to soluble forms
- Nearly always a hydrolysis process
Photosynthesis: The Essence
- Photosynthesis is the process by which plants use light energy to synthesize glucose.
- Takes place within chloroplasts and other green parts of the organisms.
- Summary equation: 6CO2+12H2O + light → C6H12O6+6O2+6H2O
Photosynthesis: Carbon Dioxide
- Carbon dioxide reaches chloroplasts in mesophyll cells by diffusion through stomata.
- Increased carbon dioxide in the atmosphere from fossil fuels, deforestation, and other human activities is a concern for climate change.
- Increased atmospheric carbon dioxide can enhance photosynthesis in some plants.
Photosynthesis: Water
- Most of the water absorbed by plants is used in transpiration, the process of water movement through a plant and its evaporation from leaves.
- Less than 1% of the water absorbed by plants is used in photosynthesis.
- Water is the source of electrons for photosynthesis and oxygen is released as a byproduct.
Photosynthesis: Light
- About 40% of the radiant energy received on Earth is in the form of visible light.
- Violet to blue and red-orange to red wavelengths are absorbed most effectively.
- Green light is reflected, which is why plants appear green.
Photosynthesis: Optimal Rates and Limiting Factors
- Different plants vary in their optimal light intensities for photosynthesis.
- Photosynthesis can also be limited by temperature and amount of carbon dioxide.
Photosynthesis: Effects of Changing Light and Temperature
- When light intensity is too high, photooxidation occurs, leading to destruction of chlorophyll.
- When light intensity is too high or water is scarce, stomata close, reducing carbon dioxide intake for photosynthesis.
- High temperatures can lead to photorespiration, using oxygen and releasing carbon dioxide, a process that may help some plants survive adverse conditions.
Photosynthesis: Chlorophyll
- There are various types of chlorophyll molecules. Magnesium is the central atom involved in light capture.
- Most plants contain chlorophyll a (blue-green) and chlorophyll b (yellow-green).
- Chlorophyll b captures light energy and transfers it to chlorophyll a, expanding the range of light wavelengths that can drive photosynthesis.
Photosynthesis: Photosynthetic Pigments
- Other photosynthetic pigments: carotenoids (yellow and orange), phycobilins (blue or red)
- 250-400 pigment molecules are grouped together in a light-harvesting complex.
- Two types of photosynthetic units work together in the light-dependent reactions of photosynthesis.
Photosynthesis: The Major Steps
- Photosynthesis is divided into two phases: Light-dependent reactions and Light-independent reactions.
Photosynthesis: Light-Dependent Reactions
- Occur in the thylakoid membranes of chloroplasts.
- Water molecules are split apart, releasing electrons and hydrogen ions.
- Electrons are passed through the electron transport system, producing ATP.
- NADP is reduced, forming NADPH, which is used in the light-independent reaction.
Photosynthesis: Light-Independent Reactions
- Occur in the stroma of chloroplasts.
- Utilize ATP and NADPH to form sugars.
- Carbon dioxide is combined with RuBP (ribulose bisphosphate) through the Calvin Cycle to produce sugars.
Photosynthesis: A Simplified Summary
- Photosynthesis is a complex process with many intermediate steps that are critical for life on Earth.
Photosynthesis: Historical Discoveries
- 1772: Joseph Priestly found that plants "restored" air.
- 1779: Jan Ingen-Housz concluded that plants only restore air when exposed to sunlight.
- 1782: Jean Senebier identified that photosynthesis requires carbon dioxide.
- 1796: Ingen-Housz demonstrated that carbon is a plant nutrient.
- 1804: Theodore de Saussure confirmed the importance of water in photosynthesis.
Photosynthesis: Light-Dependent Reactions Reexamined
- White light can be separated into different colors using a prism.
- Each pigment has a distinctive absorption spectrum.
- Shorter wavelengths carry more energy.
Photosynthesis: Light Absorption by Chlorophyll
- Chlorophyll absorbs light primarily in the violet-blue and red wavelengths.
Photosynthesis: Pigment Absorption of Light
- When a pigment absorbs light, electrons in the pigment are raised to higher energy levels, an excited state.
- Energy is released when an electron drops back to its ground state, which can occur through fluorescence, phosphorescence, or heat.
- In photosynthesis, energy is stored in chemical bonds.
Photosynthesis: The Light-Dependent Reactions Reexamined
- There are two types of photosynthetic units, photosystem I and photosystem II.
- Photosystem II occurs before photosystem I.
- Both produce ATP, but only organisms with both photosystems can produce NADPH and oxygen.
Photosynthesis: Photosystems I and II
- Photosystem I: contains chlorophyll a, small amounts of chlorophyll b, carotenoid pigments, and P700, the reaction-center molecule.
- Photosystem II: contains chlorophyll a, beta-carotene, small amounts of chlorophyll b, and the reaction-center molecule P680.
Photosynthesis: The Light-Dependent Reactions
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Photolysis: Water-splitting occurs in photosystem II. Photons excite electrons in P680, these electrons are passed through the electron transport system to photosystem I. Electrons extracted from water replace those lost by P680. Two water molecules yield one oxygen molecule, four protons, and four electrons.
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Electron transport systems: consist of cytochromes, other electron transfer molecules, and plastocyanin. Photons move across the thylakoid membrane by chemiosmosis. ATP is formed from ADP through phosphorylation.
Photosynthesis: The 4-Carbon Pathway
- Found in sugarcane, corn, sorghum, and other plants adapted to hot, dry environments.
- Instead of a 3-carbon compound (PGA), the 4-carbon pathway produces a 4-carbon compound in the initial steps of the light-independent reaction.
- These plants have Kranz anatomy, with mesophyll cells and bundle sheath cells.
Photosynthesis: Specifics of the 4-Carbon Pathway
- CO2 from the atmosphere is converted to organic acids in mesophyll cells.
- PEP (phosphoenolpyruvate) and CO2 combine to form oxaloacetic acid, instead of PGA.
- CO2 is transported as organic acids to bundle sheath cells, where it is released and enters the Calvin cycle.
Photosynthesis: C4 Plants
- Features: Kranz anatomy, high concentrations of PEP carboxylase, and the ability to efficiently utilize CO2 at lower concentrations than C3 plants.
- C4 plants thrive in conditions that are unfavorable for C3 plants.
Photosynthesis: C4 Photosynthesis Pathway
- The 4-carbon pathway is more energy-intensive than the C3 pathway, requiring 2 additional ATP molecules. C4 plants are more efficient at higher temperatures.
Photosynthesis: CAM Photosynthesis
- Crassulacean Acid Metabolism, found in succulents such as cacti, stonecrops, orchids, and bromeliads.
- Stomata open during the night, allowing CO2 to enter and be stored as organic acids.
- During the day, when stomata are closed to conserve water, the CO2 stored as organic acids is released and used in the Calvin cycle.
- This allows CAM plants to survive in arid conditions with limited water availability.
Photosynthesis: CAM and C4 Plants
- CAM photosynthesis shares similarities with C4 photosynthesis, both using the C4 pathway and producing 4-carbon compounds. However, CAM plants convert these compounds back to CO2 during the day for use in the Calvin cycle.
Photosynthesis: Significant Processes in Chloroplasts
- Sulfate to sulfide reduction: Sulfides are used to synthesize amino acids.
- Nitrate to ammonia conversion: Ammonia is used in amino acid synthesis and glutamine production.
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Description
This quiz covers the fundamental concepts of plant metabolism including photosynthesis, respiration, and the role of enzymes. Explore how energy is transferred within biochemical processes and the differences between aerobic and anaerobic respiration. Test your understanding of these essential biological mechanisms.
