Questions and Answers
Phototropism is the growth of a plant in response to ______.
light
Plants conserve water by telling their stomata to ______ when they cannot obtain enough moisture.
close
Photosynthesis increases as light intensity ______.
increases
Auxins cause cell elongation by loosening hydrogen bonds between ______ fibres.
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Plant hormones such as Auxins, gibberellins, and cytokinins are all classified as ______.
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A tropism is the growth response of a plant to an external ______.
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Stems are positively ______ and negatively geotrophic.
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Auxins are widely used in ______ powders to promote root growth.
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Hydrotropism describes the growth response of a plant to ______.
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Cytokinins are used in micropropagation to promote cell ______.
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Increased auxin concentration can lead to ______ growth in shoots.
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Geotropism is the growth response of a plant to ______.
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Phototropism ensures that stems grow towards ______.
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Ethylene is used to ______ fruit.
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Chilies have oils that deter ______ from consuming them.
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Study Notes
Growth Regulation
- Plant growth involves interactions among various growth regulators, requiring coordination and sequence.
- Growth factors are categorized as external (environmental) and internal (physiological).
External Factors
- Temperature: Affects growth; extreme heat triggers heat shock proteins to protect against protein denaturation.
- Day Length: Longer days stimulate growth and reproduction; shorter days prompt deciduous trees to shed leaves to eliminate waste.
- Light Intensity: Increased light enhances photosynthesis, resulting in improved growth and productivity.
- Water Availability: Insufficient water leads to stomatal closure to conserve moisture.
Internal Factors
- Growth Regulators: Includes plant hormones like auxins, gibberellins, cytokinins, and ethylene.
- Injury and Disease: Trigger chemical responses, including the production of phytoalexins for defense.
Categories of Growth Regulators
- Promoters: Stimulate growth (e.g., Auxins).
- Inhibitors: Suppress growth (e.g., Abscisic acid).
Auxins
- Indole Acetic Acid (IAA) is the most prevalent auxin, primarily produced in the apical meristem.
- Auxins facilitate stem elongation and root/shoot development; they affect growth by loosening cellulose bonds and increasing water uptake.
- Lower auxin concentrations can promote growth in shoots while inhibiting growth in roots.
Uses of Growth Regulators
- Auxins: Commonly utilized in rooting powders to enhance adventitious root formation.
- Cytokinins: Aid in cell differentiation during micropropagation.
- Ethylene: Employed for ripening fruits.
Tropisms
- Definition: Tropisms are directional growth responses to stimuli that optimize plant positioning.
- Phototropism: Stems grow towards light; roots grow away from light.
- Chemotropism: Roots grow towards beneficial chemicals like minerals.
- Thigmotropism: Growth in response to touch (e.g., ivy).
- Geotropism: Roots grow downward in response to gravity, seeking water and minerals.
- Hydrotropism: Growth response to water availability.
Plant Adaptations for Protection
- Chilies: Contain oils causing a burning sensation to deter herbivores.
- Nettles: Have stings with formic acid to discourage feeding and handling.
- Hawthorn bush: Sharp thorns to prevent animals from feeding.
- Gorse: Hard, stiff leaves to deter browsers.
Auxins and Growth Responses
- Auxins play a crucial role in phototropism and apical dominance.
Phototropism Study
- Conducted by Charles Darwin, showed the growth tip regulates light response via chemical signals.
- The discovery of a mobile chemical signal that promotes bending towards light confirmed auxins’ role.
- Unilateral light exposure increases auxin concentration on the shaded side, resulting in differential growth.
Apical Dominance
- Auxin from the stem's apical meristem inhibits lateral bud growth, maintaining dormancy.
- As auxin levels decrease down the stem, lateral buds begin to develop once a threshold concentration is reached.
- Removal of the apical bud halts IAA production, allowing all lateral buds to grow, leading to bushier plants.
Concentration Effects
- Auxin concentrations have varying impacts on different plant regions, demonstrating complexity in hormonal responses.
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Description
Explore how plants respond to various stimuli through the interaction of growth regulators. This quiz covers both external and internal factors that influence plant growth and development, highlighting the importance of regulatory sequences. Test your knowledge on how temperature and other elements affect plant responses.
