Questions and Answers
What carbon sources do aquatic photosynthetic organisms use?
Dissolved CO2, bicarbonates, and soluble carbonates
What is the atmospheric concentration of CO2?
0.03 - 0.04 percent
Stomata are responsible for the entry of CO2 into the leaves during photosynthesis.
True
What regulates the opening and closing of stomata?
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Which processes are part of photosynthesis?
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What molecules are produced during light-dependent reactions?
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Which type of molecule serves as the main energy carrier in cells?
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What is the primary function of the Calvin cycle in photosynthesis?
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Which of the following enzymes is involved in the Calvin cycle?
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The dark reactions of photosynthesis can only occur in the presence of light.
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Match the following photosynthetic pigments with their associated functions:
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The process of energy synthesis in both cyclic and non-cyclic photophosphorylation is called ______.
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What are the two main types of respiration in living organisms?
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What is the end product of glycolysis?
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What is bioenergetics?
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Which of the following is a product of photosynthesis?
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Photosynthesis occurs both day and night.
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What is the function of chlorophyll in photosynthesis?
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What is the overall equation for photosynthesis?
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Plants release oxygen during ______.
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What is the source of oxygen released during photosynthesis?
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What is the role of NADPH in photosynthesis?
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What are accessory pigments in chloroplasts used for?
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Chlorophyll a is the only pigment involved in the light-dependent reactions.
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Who proposed that water is the source of oxygen during photosynthesis?
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What does the absorption spectrum indicate?
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Photosynthesis contributes to the carbon dioxide concentration in the atmosphere.
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Chlorophyll is mainly located in the ______ of plant cells.
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Which of the following chlorophylls absorbs mainly in the blue-green range?
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Hydroponics are the plants grown in water culture.
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Calcium is an essential element for chlorophyll formation.
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Chlorosis means yellowing of leaves due to deficiency of certain essential elements of plant nutrition.
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List four features of a leaf which show that it is able to carry out photosynthesis effectively.
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Summarise the role of water in photosynthesis.
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What are T.W. Engelman and Melvin Calvin famous for?
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What is the difference between an action spectrum and an absorption spectrum?
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What is the role of accessory pigments in light absorption?
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When and why is there not a net exchange of CO2 and O2 between the leaves and the atmosphere?
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What is the net production of ATP during glycolysis?
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What is the main difference between photophosphorylation and oxidative phosphorylation?
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What is the location of the electron transport chain (ETC) and chemiosmosis in photosynthesis and cellular respiration?
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How did the evolution of photosynthesis affect the metabolic pathway?
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How does the absorption spectrum of chlorophyll a differ from that of chlorophyll b?
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Why are the carotenoids usually not obvious in the leaves?
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How is the formation of vitamin A linked with the eating of carrots?
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Explain the roles of NAD+ and FAD in aerobic respiration.
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Summarise how much energy (as ATP) is made available to the cell from a single glucose molecule by glycolysis, the formation of acetyl CoA, the citric acid cycle, and the electron transport chain.
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Trace the fate of hydrogen atoms removed from glucose during glycolysis when oxygen is present in muscle cells; compare this to the fate of hydrogen atoms removed from glucose when oxygen is insufficient to support aerobic respiration.
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Sketch Krebs cycle and discuss its energy yielding steps.
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Describe various steps involved in oxidative breakdown of glucose to pyruvate.
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Sketch respiratory electron transport chain. Discuss the significance of ETC.
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Compare photosynthesis with respiration in plants.
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Explain the difference between cyclic and non-cyclic photophosphorylation with the help of the Z scheme.
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Give an account of light-independent reactions of photosynthesis.
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Study Notes
Bioenergetics Overview
- Bioenergetics studies energy relationships and conversions in biological systems, adhering to thermodynamics.
- All living organisms require free energy for survival, sourced primarily from solar energy.
- While organisms can't use sunlight directly, they utilize chemical energy from food, like sugars.
Photosynthesis
- Photosynthesis converts low-energy inorganic carbon (CO2) and hydrogen (water) into high-energy carbohydrates (glucose) using light energy, primarily through chlorophyll.
- Overall photosynthesis equation:
6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O - Photosynthesis produces glucose and oxygen, while respiration uses products of photosynthesis.
- Photosynthesis occurs only during daylight, contra respiration which happens day and night.
Compensation Point
- At twilight, the rates of photosynthesis and respiration may equal, resulting in no net gas exchange; termed the compensation point.
- Increased light intensity boosts photosynthesis, leading to higher CO2 demand, and oxygen release surpasses cellular respiration needs.
Source of Atmospheric Oxygen
- Oxygen produced during photosynthesis derives from the splitting of water, confirmed through isotopic tracer experiments involving heavy oxygen (O18).
Chloroplasts
- Chloroplasts, located in the mesophyll cells of leaves, are the primary sites for photosynthesis.
- Each chloroplast contains thylakoids where light reactions occur and stroma for the dark reactions.
- Chlorophylls embedded in thylakoid membranes absorb sunlight, generating ATP and NADPH.
Photosynthetic Pigments
- Pigments absorb specific visible light wavelengths (380-750 nm); chlorophylls are the main pigments.
- Accessory pigments, like carotenoids, broaden light absorption spectrum, protecting chlorophyll from excess light.
- Absorption spectrum for chlorophyll peaks at blue (~430 nm) and red (~670 nm) wavelengths.
Light as Energy Source
- Light is electromagnetic energy crucial for photosynthesis, but only about 1% is absorbed by leaves.
- Action spectrum studies show that photosynthesis is most effective where chlorophyll absorbs light, though carotenoids enhance energy transfer.
Role of Carbon Dioxide
- CO2 is essential for photosynthesis; terrestrial plants utilize atmospheric CO2, while aquatic organisms use dissolved forms.
- Stomata regulate CO2 intake, opening during the day and closing at night, influenced by guard cells' structure and rhythm.
Reactions of Photosynthesis
- Photosynthesis is a redox process composed of light-dependent (light) and light-independent (dark) reactions.
- Light-dependent reactions harness sunlight directly, while dark reactions utilize products of the light phase (ATP and NADPH) to convert CO2 into sugars.### Photosynthesis Overview
- Photosynthesis consists of light-dependent reactions (energy conversion) and light-independent reactions (energy conservation) that convert light energy into chemical energy stored in glucose.
- Light-dependent reactions convert solar energy into ATP and NADPH, which provide power for the synthesis of sugars in the Calvin cycle.
Light-Dependent Reactions
- Occur in thylakoid membranes, where photosynthetic pigments absorb sunlight, organized into photosystems (PS I and PS II).
- PS II absorbs light at 680 nm (P680), while PS I absorbs at 700 nm (P700).
- Light energy excites electrons in chlorophyll at the reaction centers, initiating electron transport.
- The primary electron acceptor captures excited electrons from chlorophyll, leading to ATP production via chemiosmosis.
- Non-cyclic electron flow involves both photosystems, producing ATP and NADPH and releasing oxygen from photolysis of water.
- Cyclic electron flow involves only PS I and generates ATP but no oxygen or NADPH.
Photophosphorylation
- ATP synthesis occurs during the light-dependent reactions driven by light energy.
- Non-cyclic photophosphorylation produces ATP through a series of redox reactions involving electron transport chains and protons (H+) gradients in thylakoid membranes.
Light-Independent Reactions (Calvin Cycle)
- Occur in the stroma of chloroplasts, using ATP and NADPH from light reactions to convert carbon dioxide into sugars.
- The process consists of three stages: Carbon Fixation, Reduction, and Regeneration of RuBP.
- Carbon fixation incorporates CO2 into ribulose bisphosphate (RuBP) via Rubisco, forming a 6-carbon intermediate that splits into two 3-carbon molecules (3-PGA).
- Reduction converts PGA into glyceraldehyde 3-phosphate (G3P) using ATP and NADPH, yielding one net G3P for every six produced.
- Regeneration of RuBP occurs with the rearrangement of G3P molecules, allowing the cycle to continue.
Respiration
- Respiration is the metabolic process that provides energy to cells by breaking down carbon compounds.
- Involves both external respiration (gas exchange) and cellular respiration (energy production).
- Cellular respiration can be aerobic (with oxygen) or anaerobic (without oxygen).
- Glycolysis splits glucose into pyruvate in the cytosol; oxygen availability determines the next steps.
Anaerobic Respiration
- Alcoholic fermentation converts pyruvic acid into alcohol and CO2 in yeast.
- Lactic acid fermentation converts pyruvic acid into lactic acid in anaerobic conditions, such as intense muscle activity.
- Both fermentation pathways yield small energy amounts from glucose compared to aerobic respiration.
Role of Mitochondria
- Mitochondria serve as cellular powerhouses, responsible for ATP production through respiration processes.
- They have an outer membrane and an inner membrane organized into cristae, creating compartments that facilitate energy transfer via enzymes.
Adenosine Triphosphate (ATP)
- ATP is a key energy carrier in cells, composed of adenine, ribose, and three phosphate groups.
- The terminal phosphate bond releases energy (approximately 7.3 Kcal) upon hydrolysis, essential for various cellular processes like muscle contraction and active transport.
Biological Oxidation & Cellular Respiration
- Biological oxidation involves energy-releasing reactions, primarily through oxidation-reduction processes.
- Cellular respiration stages include glycolysis (anaerobic), pyruvic acid oxidation, Krebs cycle, and the respiratory chain (aerobic).
- Glycolysis occurs in the cytosol, while subsequent stages occur in mitochondria, requiring oxygen for efficiency.### Glycolysis
- Glycolysis breaks down glucose into pyruvic acid in both aerobic and anaerobic conditions.
- It occurs in the cytosol and involves a series of enzyme-catalyzed steps.
- ATP and NAD (nicotinamide adenine dinucleotide) are essential for glycolysis.
- Divided into two phases: preparatory phase and oxidative phase.
Preparatory Phase
- The first step involves transferring a phosphate from ATP to glucose creating glucose-6-phosphate.
- Glucose-6-phosphate is converted into fructose-6-phosphate.
- Another ATP adds a second phosphate, forming fructose 1,6-bisphosphate.
- Fructose 1,6-bisphosphate splits into two three-carbon molecules: G3P and dihydroxyacetone phosphate (DHAP).
Oxidative Phase
- PGAL (3-phosphoglyceraldehyde) is oxidized, transferring electrons to NAD, forming NADH.
- Inorganic phosphate adds to PGAL, producing 1,3-bisphosphoglycerate (BPG).
- A phosphate from BPG transfers to ADP, forming ATP and producing 3-phosphoglycerate (3-PG).
- 3-PG is further processed into 2-phosphoglycerate (2-PG), which transforms into phosphoenolpyruvate (PEP).
- PEP donates its phosphate to ADP, yielding ATP and resulting in pyruvate.
Pyruvic Acid Oxidation
- Pyruvate is converted into acetic acid (2-carbon) through decarboxylation, releasing CO2.
- Acetic acid binds with coenzyme-A to form acetyl CoA.
- Hydrogen atoms are transferred to NAD during this conversion.
Krebs Cycle (Citric Acid Cycle)
- Acetyl CoA enters the Krebs cycle, combining with oxaloacetate to produce citrate (6-carbon).
- The cycle involves a series of reactions, including the production of isocitrate and further oxidations.
- Decarboxylation occurs, yielding a-ketoglutarate.
- ATP is synthesized from the energy changes during the conversion of a-ketoglutarate to succinate.
- Succinate is oxidized to fumarate, with FAD reducing to FADH2.
Completion of the Krebs Cycle
- Fumarate converts to malate through hydration.
- Malate undergoes another oxidation to regenerate oxaloacetate, completing the cycle.
Respiratory Chain and Oxidative Phosphorylation
- NADH and H+ produced in the Krebs cycle transfer electrons to the respiratory chain.
- Coenzyme Q and cytochromes aid in electron transport and oxidation-reduction reactions.
- Electrons ultimately reduce oxygen, forming water and enabling ATP synthesis via oxidative phosphorylation.
Oxidative Phosphorylation Mechanism
- Occurs within the inner mitochondrial membrane through chemiosmosis.
- Proton movement across the membrane drives ATP synthesis.
- Each pair of H atoms entering the chain yields three ATP molecules.
Other Key Points
- Hydroponics refers to plants grown in nutrient-rich water solutions.
- Calcium is critical for chlorophyll formation and overall plant health.
- Chlorosis is a condition of yellowing leaves due to nutrient deficiency.
Energy Yield Summary
- Glycolysis, formation of acetyl CoA, Krebs cycle, and electron transport chain release total ATP from a single glucose molecule.
- Comparison of conditions with sufficient and insufficient oxygen availability influences hydrogen atom fate during respiration.
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Description
Explore the concepts of bioenergetics in this quiz, focusing on the quantitative study of energy relationships and conversions in biological systems. Understand how organisms rely on free energy to remain functional, all while adhering to the principles of thermodynamics.