1. What are plant hormones, and how do they influence plant growth and development?
Answer: Plant hormones, also known as phytohormones, are chemical substances that regulate various aspects of plant growth and development. They influence processes such as germination, flowering, fruit ripening, response to light, and stress. These hormones are produced in specific parts of the plant and act in different locations, either enhancing or inhibiting specific growth processes.
2. Describe the role of Auxins in plant growth and development.
Answer: Auxins are a group of plant hormones that play a crucial role in cell elongation, phototropism, gravitropism, and root initiation. They are primarily produced in the tips of shoots and roots. Auxins promote the elongation of cells in the stem and are involved in the process of apical dominance, where the main stem grows more vigorously than the side shoots.
3. How do Auxins contribute to phototropism in plants?
Answer: Auxins are involved in phototropism, which is the directional growth of plants in response to light. When a plant is exposed to light from one direction, auxins accumulate on the shaded side of the plant stem. This accumulation causes the cells on the shaded side to elongate more than those on the light-exposed side, causing the plant to bend toward the light.
4. Explain the role of Gibberellins in seed germination.
Answer: Gibberellins are plant hormones that promote seed germination. They break seed dormancy by stimulating the synthesis of enzymes like amylases, which help in the conversion of stored starches into sugars. These sugars are then used as energy for the growth of the seedling. Gibberellins also promote elongation of the stem and flowering in some plants.
5. What is the effect of Gibberellins on plant height?
Answer: Gibberellins stimulate cell division and elongation, leading to an increase in plant height. This is especially evident in plants that exhibit excessive elongation or “bolting” when exposed to high levels of gibberellins. The hormone promotes stem growth, making the plant taller and stronger.
6. Discuss the role of Cytokinins in plant cell division and growth.
Answer: Cytokinins are hormones that promote cell division, or cytokinesis, in plants. They are often synthesized in the roots and then transported to other parts of the plant. Cytokinins stimulate the growth of lateral buds and help in delaying the aging of plant tissues by promoting the synthesis of proteins involved in cell division and growth.
7. How do Cytokinins influence leaf senescence?
Answer: Cytokinins delay leaf senescence, which is the process of aging and death of plant leaves. They do so by promoting protein synthesis and encouraging the maintenance of chlorophyll, which helps in photosynthesis. As a result, cytokinins help in extending the functional life of leaves and maintaining the plant’s overall health.
8. What is apical dominance, and how do Auxins play a role in it?
Answer: Apical dominance refers to the suppression of lateral bud growth in the presence of an actively growing apical bud (the tip of the plant shoot). Auxins produced in the apical bud inhibit the growth of lateral buds, ensuring that the plant grows upwards and not sideways. This helps the plant access more light and nutrients.
9. What are the differences between Auxins, Gibberellins, and Cytokinins in terms of their effects on plant growth?
Answer: Auxins primarily promote cell elongation and are involved in processes like phototropism and gravitropism. Gibberellins promote stem elongation and seed germination, and they are also involved in flowering and fruit development. Cytokinins, on the other hand, promote cell division, stimulate lateral bud growth, and delay leaf senescence. Each hormone plays a distinct yet complementary role in regulating plant growth.
10. Explain how Gibberellins are used in agricultural practices.
Answer: Gibberellins are used in agriculture to enhance plant growth and development. They are commonly applied to induce seed germination, especially in seeds that require breaking dormancy. Gibberellins are also used to increase the size of fruits like grapes, to promote flowering in certain crops, and to enhance the overall height and yield of plants such as rice and barley.
11. Describe how Auxins are used in the propagation of plants.
Answer: Auxins are used in plant propagation to encourage root formation in cuttings. When a stem or leaf cutting is treated with auxins, the hormone stimulates the formation of adventitious roots, aiding in the successful rooting of the cutting. This is widely used in horticulture to propagate plants without the need for seeds.
12. How does the balance of Auxins and Cytokinins affect plant tissue culture?
Answer: In plant tissue culture, the balance between auxins and cytokinins determines whether the cultured cells will develop into roots or shoots. A high concentration of auxins promotes root formation, while a high concentration of cytokinins promotes shoot development. By adjusting the levels of these hormones, scientists can manipulate the growth of plant tissues for various purposes.
13. What are some agricultural benefits of Cytokinins?
Answer: Cytokinins are used in agriculture to promote the growth of shoots and lateral buds. They can be applied to increase branching in plants, improve fruit setting, and delay leaf aging. Cytokinins also enhance the overall growth of crops by improving nutrient assimilation and prolonging the vitality of plant tissues.
14. Explain the concept of plant hormone interaction using Auxins, Gibberellins, and Cytokinins.
Answer: The growth and development of plants are regulated by a complex interplay between different hormones. For example, auxins and gibberellins often work together to promote stem elongation, while cytokinins balance their effects by encouraging cell division and branching. The interaction of these hormones ensures that the plant grows in a coordinated manner, with the right balance between elongation, division, and differentiation.
15. How do plant hormones affect the process of fruit ripening?
Answer: Auxins, gibberellins, and cytokinins all play a role in fruit ripening. Auxins delay the ripening process by inhibiting ethylene production, while gibberellins can stimulate fruit enlargement and soften the fruit, enhancing ripening. Cytokinins, in some cases, delay ripening by prolonging the activity of chlorophyll in fruits.
16. What is the significance of Auxin-Gibberellin interaction in fruit development?
Answer: The interaction between auxins and gibberellins is crucial for the proper development and growth of fruits. While auxins promote fruit setting by stimulating cell division, gibberellins help in enlarging the fruit by promoting cell elongation. Both hormones are essential for achieving optimal fruit size and quality.
17. Discuss the role of plant hormones in response to environmental stresses.
Answer: Plant hormones play a key role in helping plants respond to environmental stresses. For example, auxins help plants bend toward light in low-light conditions (phototropism) and allow them to respond to gravity (gravitropism). Gibberellins can promote growth when the plant is under stress, and cytokinins help maintain healthy tissues, delaying senescence under drought conditions.
18. What are the physiological effects of synthetic Auxins used in agriculture?
Answer: Synthetic auxins, like 2,4-D, are widely used in agriculture as herbicides. They mimic the action of natural auxins and cause uncontrolled growth in broadleaf plants, leading to their death. They are also used in rooting hormones to stimulate the development of roots in plant cuttings, aiding in plant propagation.
19. What is the relationship between Gibberellins and flowering in plants?
Answer: Gibberellins play a role in the flowering of certain plants by promoting the transition from vegetative growth to reproductive growth. In some plants, gibberellins are required for flower induction, especially in long-day plants that flower in response to environmental conditions. Gibberellins can also promote the elongation of floral organs, aiding in successful pollination and seed formation.
20. How can an imbalance in plant hormones like Auxins, Gibberellins, and Cytokinins affect plant growth?
Answer: An imbalance in the levels of plant hormones can lead to abnormal growth and development. Excessive auxins can cause overgrowth or abnormal cell elongation, while too little can inhibit root growth. High levels of gibberellins can lead to excessive stem elongation, while low levels may cause dwarfing. Similarly, an imbalance in cytokinins can lead to premature senescence or poor shoot development. Proper regulation of these hormones is essential for normal plant development and growth.
These questions and answers provide a thorough overview of the roles of auxins, gibberellins, and cytokinins in plant growth and development.
