Questions and Answers
What is the primary role of abscisic acid (ABA) in relation to gibberellins (GAs) in plant growth?
Which of the following processes can be influenced by plant growth regulators (PGRs)?
In which context is ethylene primarily known to function in plants?
What type of plants require a light exposure longer than a critical duration to flower?
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Which term describes plants that do not have a correlation between light duration and flowering induction?
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How do extrinsic factors like temperature and light affect plant growth?
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Which of the following statements best explains the role of dormancy in seeds?
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Which of the following is NOT a role of plant growth regulators (PGRs)?
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What is the term for the response of plants to light and dark exposure durations?
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Which part of the plant is mainly responsible for perceiving photoperiods?
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Which phenomenon requires exposure to low temperatures for flowering to occur?
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What is the role of the hormonal substance that migrates from leaves during photoperiodism?
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What type of plant does not depend on the length of light or dark periods for flowering?
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Which statement about shoot apices is true regarding photoperiodism?
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How does vernalisation benefit a plant during the growing season?
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What balance is essential for flowering in certain plants?
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Which function is primarily associated with ethylene in plants?
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Which plant growth regulator is primarily used to encourage rooting in cuttings?
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What role does abscisic acid play during plant stress conditions?
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What is the primary effect of light on the flowering process in plants?
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Which term describes the physiological process that leads to the breaking of dormancy in seeds?
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In what scenario would cytokinin typically be omitted during tissue culture?
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What would likely happen if gibberellic acid (GA3) is applied to rice seedlings?
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How does abscisic acid influence seed germination?
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Study Notes
Plant Growth Regulators (PGRs)
- Abscisic acid (ABA) generally acts as an antagonist to gibberellins (GAs).
- PGRs play crucial roles in plant growth, differentiation, and development; these roles can be complementary, antagonistic, individualistic, or synergistic.
- Multiple PGRs often interact during events like seed/ bud dormancy, abscission, senescence, and apical dominance.
- PGRs are one aspect of intrinsic control, alongside genomic control and extrinsic factors affecting plant growth.
Extrinsic Factors Influencing Growth
- External factors like temperature and light regulate plant growth through their interaction with PGRs.
- Key processes influenced by these factors include flowering, seed germination, dormancy, and plant movements.
Photoperiodism
- Many plants require specific periods of light exposure to initiate flowering, categorized as:
- Long day plants: require exposure exceeding a critical duration.
- Short day plants: need exposure less than a critical duration.
- Day-neutral plants: show no correlation between light duration and flowering.
- Both light and dark period durations, and their ratios, are vital for the flowering response.
- Leaves are responsible for perceiving light/dark durations, sending hormonal signals to shoot apices for flowering.
Vernalisation
- Vernalisation is a process where flowering in some plants depends on exposure to low temperatures.
- This adaptation helps prevent premature reproductive development late in the growing season, allowing plants to mature properly.
Growth Patterns and Rates
- Arithmetic Growth: Increases in size at a constant amount.
- Geometric Growth: Increases in size at a constant ratio or percentage.
- Sigmoid Growth Curve: Characterized by a slow start, rapid increase, and plateau.
- Absolute Growth Rate: The total growth over a period.
- Relative Growth Rate: Growth relative to the size of the organism.
Key PGRs and Applications
- Main groups of natural plant growth regulators include auxins, gibberellins, cytokinins, ethylene, and abscisic acid.
- Specific applications for different PGRs:
- Inducing rooting in cuttings (Auxins).
- Accelerating fruit ripening (Ethylene).
- Delaying leaf senescence (Cytokinins).
- Promoting growth in axillary buds (Gibberellins).
- Initiating bolting in rosette plants (Gibberellins).
- Inducing rapid stomatal closure (Abscisic acid).
Miscellaneous Questions
- Defoliated plants do respond to photoperiodic cycles as they still possess the necessary leaf structures for perception.
- The application of GA3 to rice seedlings can promote growth and increase height.
- If dividing cells stop differentiating, growth will be stunted and the plant's development will be impaired.
- Mixing ripe fruit with unripe can trigger ripening in the unripe fruits due to ethylene production.
- Omitting cytokinin in culture mediums can halt cell division and tissue growth.
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Description
Explore the intricate roles of plant growth regulators (PGRs) like ABA and GAs in plant development. This quiz delves into how these regulators can act as antagonists or synergetic partners, influencing various growth phases. Test your understanding of plant physiology and the interplay of growth factors.
