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Questions and Answers
Which phase of plant reproduction involves the maturation of fruits and seeds?
What process occurs during the light reactions of photosynthesis?
Which of the following is a requirement for seed germination?
What is the primary function of Photosystem II in the light reactions?
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Which pathway is associated with CO2 fixation in plants?
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In which part of the chloroplast do the light reactions take place?
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Which of the following describes quiescence in seeds?
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Which type of phosphorylation occurs in the light reactions during the transfer of electrons?
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Which phase of plant growth is characterized by the highest exponential growth rate?
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What is the role of thylakoids in photosynthesis?
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During which stage of plant life cycle does a plant transition from germination to having true leaves?
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What process occurs in the stroma during photosynthesis?
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Which part of photographs involves catalyzing the removal of electrons from water molecules?
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Which phase of growth is associated with the onset of flowering?
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What is the main product of the light reactions in photosynthesis?
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What is primarily developed during the vegetative stage of plant growth?
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Which statement best describes the senescence phase of plant growth?
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What transforms light energy into chemical energy during photosynthesis?
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What is the primary product of the C3 pathway during photosynthesis?
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Which enzyme is responsible for the carboxylation in the C4 pathway?
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How do CAM plants adapt to their environment regarding water usage?
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Which method for testing seed germination involves immersion in a diluted solution to determine viability?
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Which of the following correctly describes the structure referred to as Kranz anatomy?
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What is the main function of CO2 in photosynthesis?
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Which enzyme is primarily responsible for the photorespiration process in plants?
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Which statement about C4 plants is correct?
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What is produced during light reactions of photosynthesis?
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Which factor does NOT affect the efficiency of photosynthesis?
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Which of the following is NOT a product of the Calvin cycle?
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What role does Photosynthetically Active Radiation (PAR) play in photosynthesis?
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What is typically used as a raw material in the photosynthesis general reaction?
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In which part of the plant does the Calvin cycle occur?
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Which statement accurately describes the relationship between photosynthesis and respiration?
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What is the purpose of antenna pigments in photosynthesis?
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In which type of seed germination does the cotyledon not raise above ground?
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What occurs during noncyclic photophosphorylation?
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What environmental conditions must be met for proper seed germination?
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What is mainly generated during the light reactions of photosynthesis?
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What process involves soaking seeds in water to break dormancy?
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What is the primary role of photosystems in photosynthesis?
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What is the significance of the Z-scheme in photosynthesis?
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During which phase of photosynthesis is oxygen produced?
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Which of the following methods is NOT used to break seed dormancy?
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Study Notes
Seed Dormancy & Quiescence
- Dormancy: A seed's inability to germinate due to specific environmental factors.
- Quiescence: A seed's failure to germinate due to the absence of necessary germination requirements.
Germination
- The resumption of growth in an embryo, leading to the radicle (root) emerging from the seed coat or the shoot breaking through, forming a seedling.
Stages of Germination
- Activation: The initial stage where a seed's germination process begins.
- Epigeous: Germination pattern where the hypocotyl elongates, raising the cotyledons (seed leaves) above ground. Mostly observed in dicotyledonous plants.
- Hypogeous: Germination pattern where the hypocotyl does not raise the cotyledons above ground; only the epicotyl (the part of the stem above the cotyledons) emerges.
Germination Requisites
- Seed Viability: The seed must be viable for germination to occur.
- Internal Conditions: The seed itself must have favorable internal conditions for growth.
- Proper Temperature: The appropriate temperature range is critical for germination.
- Oxygen: Adequate oxygen supply is needed for cellular respiration during germination
- Environmental Conditions: The surrounding environment must be conducive to germination, such as humidity.
Methods of Breaking Dormancy
- Soaking In Water: Exposing seeds to cold or warm water can break dormancy.
- Scarification: Mechanical or chemical treatment to scarify the seed coat, facilitating germination.
- Stratification: Storing seeds in a high-moisture and low-temperature environment to induce germination.
- Chemical Treatments: The use of chemicals like potassium nitrate (KNO3), thiourea, hydrogen peroxide, and growth regulators to stimulate germination.
- Breaking the Seedcoat: Removing the hilum covering can sometimes resolve seed coat dormancy.
Methods of Testing Seed Germination
- Ragdoll: This method involves placing seeds on a piece of cloth, which is then rolled up and placed in a container with moisture. The germination percentage is then calculated.
- Seedbox Method: Seeds are sown in a box with a specific type of medium, and the germination percentage is calculated.
- Petri Dish Method: Seeds are placed on filter paper in a petri dish with a suitable solution, and germination is monitored.
- Tetrazolium Test: A solution of 2,3,5-triphenyltetrazolium chloride, a colorless solution, is used to assess seed viability. Seeds are placed in the solution, and the resulting color change (darker) indicates a sound, viable seed.
Photosynthesis (PS)
- General Equation: CO2 + H2O + Light → CH2O + O2
- Photosynthetically Active Radiation (PAR): Wavelengths from 380 nm (violet) to 760 nm (red) in the visible part of the electromagnetic spectrum.
- Processes, Products and Sites:
- Sucrose synthesis: Occurs in the cytosol
- Triose phosphate synthesis: Occurs in the chloroplast stroma
- Calvin Cycle: The cycle in which carbon dioxide is converted into sugars; occurs in the chloroplast stroma
- NADPH and ATP generation: Produced during the light reactions in the chloroplast thylakoids.
- Oxygen production: Released during the light reactions in the chloroplast thylakoids.
- Water uptake: Water is taken up from the soil for photosynthetic processes.
- CO2 uptake: Carbon dioxide enters the plant through stomata.
Crop Yield & Photosynthesis
- Crop yield is affected by the efficiency of the photosynthetic process.
Factors Affecting Photosynthesis
- Light: Quantity and quality of light are key factors.
- CO2 Concentration: Availability of CO2 in the atmosphere.
- Leaf Diffusive Resistance: The resistance of the leaf surface to gas movement.
- Temperature: Optimal temperature range for photosynthetic activity.
- Water: Sufficient water availability is crucial for photosynthesis.
- Leaf Age: Various age groups of leaves have different photosynthetic rates.
- Mineral Status: The presence of essential minerals in plants influence the efficiency of photosynthesis.
Photosynthetic Apparatus
- The chloroplast is the primary site of photosynthesis.
Respiration
- Importance: Generates NADH and ATP, which are essential energy carriers; provides the carbon skeletons needed for compound synthesis.
- Water: Comes from the soil.
- CO2 Movement: CO2 enters and exits through stomata.
Respiration Sites:
- Light Reaction: The thylakoid membrane of the chloroplast, where solar energy is transformed into chemical energy.
- Dark Reaction: The stroma of the chloroplast, where CO2 is reduced in the Calvin Cycle.
Reaction Centers
- Photosystem I and II: Play a crucial role in the light reactions of photosynthesis.
- Photosystem II: Catalyzes the removal of electrons from water molecules (photolysis, the process of splitting water).
- Photosystem I: Absorbs light energy independently, but its core component receives electrons from Photosystem II.
Z-Scheme and Hill Reaction (Non-cyclic Photophosphorylation):
- Light reactions occur across the thylakoid membrane.
- Electrons are transferred from water to NADP+ (nicotinamide adenine dinucleotide phosphate), accompanied by H+ ion transport.
- The energy in the electron transport chain is used to generate ATP by ATP synthase.
Cyclic Photophosphorylation:
- Electrons from Photosystem I cycle back through ferredoxin and some components of the electron transport system, causing ATP production.
Light and Dark Phases
- Non-cyclic photophosphorylation and cyclic photophosphorylation generate NADPH and ATP in the light phase and are utilized in the dark phase (Calvin Cycle) for CO2 fixation and sugar synthesis.
CO2 Fixation
- C3 Pathway: The first stable product of the Calvin Cycle is 3-phosphoglyceric acid (3-PGA). The first step is the carboxylation of RuBP (ribulose bisphosphate) to form two molecules of 3-PGA by the enzyme RuBP carboxylase (rubisco).
- C4 Pathway: The first product is oxaloacetic acid, formed by the carboxylation of PEP (phosphoenolpyruvate) catalyzed by the enzyme PEP carboxylase.
- Kranz Anatomy: A specialized cell organization seen in C4 plants:
- Bundle Sheath Cells: Surround the vascular bundles.
- Mesophyll Cells: Surrounding the bundle sheath cells.
- Crassulacean Acid Metabolism (CAM): Used by plants that grow in areas with minimal water availability.
- Stomata: Close during the day and open at night.
- Malic Acid: CO2 is fixed at night to form malic acid, which is stored in the vacuole.
- Decarboxylation: Malic acid is decarboxylated during the day, releasing CO2 for the Calvin cycle.
C3 vs C4 Pathways
- C4 plants have a higher ratio of CO2 to O2 within their photosynthetic cells, effectively minimizing photorespiration.
- C4 plants maintain higher photosynthetic efficiency, as they can fix CO2 more efficiently.
Photorespiration
- A process in plant metabolism where the enzyme RuBisCO (found in C3 plants) oxygenates RuBP, causing some of the energy produced by photosynthesis to be wasted.
Phases of Plant Growth:
- Lag Phase: Early vegetative growth.
- Log Phase: Grand period of growth where growth rate is exponential.
- Declining Phase: Flowering onset is offset by leaf fall
- Steady Phase: Grain filling and ripening continue steadily.
- Senescence: Characterized by death of the plant and its parts.
Stages of Plant Development
- Seedling Stage: Begins with germination and ends when true leaves develop.
- Vegetative Stage: Juvenile stage between seedling and flowering, characterized by the growth of the root system and foliage.
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Description
Test your knowledge on the various aspects of seed dormancy, quiescence, and the stages of germination. This quiz covers essential concepts such as activation, epigeous and hypogeous germination patterns, and the requisites for successful germination. Perfect for students studying plant biology.
