Control Of Plant Growth & Responses Outline Quiz

When a plant is laid on its side, the cells on the lower side of the stem will respond to gravity by elongating. This elongation causes the stem to turn and grow in an upward direction, allowing the plant to continue its growth towards the light source. This response is known as gravitropism, which is a plant's ability to sense and respond to gravity. Therefore, the statement is true.

Positive gravitropism is the correct answer because it refers to the growth or movement of a plant part in response to the force of gravity. In the case of roots, positive gravitropism causes them to grow downward, towards the gravitational pull. This allows the roots to anchor the plant in the soil and absorb water and nutrients effectively.

Thigmotropism is the growth or movement of a plant in response to touch or contact with a solid object. In the case of a pea vine, it twines around a wire support due to thigmotropism. When the vine comes into contact with the wire, it senses the touch and responds by growing and wrapping itself around the support. This allows the vine to climb and support itself as it grows.

Abscisic acid is known as the stress hormone because it induces dormancy in seeds and buds. It plays a crucial role in regulating plant responses to environmental stresses such as drought, cold, and salinity. Abscisic acid inhibits seed germination and promotes seed dormancy, allowing plants to survive unfavorable conditions. It also promotes the closure of stomata to reduce water loss in response to water stress. Overall, abscisic acid helps plants adapt and survive during periods of stress.

Ethylene is a plant hormone that stimulates the ripening of fruit and inhibits plant growth. It is responsible for processes such as fruit softening, color change, and aroma production during ripening. Ethylene also regulates various physiological processes in plants, including leaf and flower senescence, abscission (shedding of leaves and fruits), and response to stress. It acts as a signaling molecule, promoting the breakdown of cell walls and leading to the characteristic changes observed during fruit ripening.

Plant hormones are generally produced in meristem tissues. Meristems are regions of actively dividing cells in plants, responsible for growth and development. They are found at the tips of roots and shoots, as well as in the cambium, which is responsible for secondary growth. Since plant hormones play a crucial role in regulating various physiological processes, such as cell elongation, differentiation, and organ formation, it makes sense that they are produced in tissues that are actively undergoing growth and development, like meristems.

Cytokinins are a type of plant hormone that play a crucial role in preventing plant tissues from senescing or aging. They promote cell division and delay the aging process, allowing plants to maintain their vitality and prolong their lifespan. Cytokinins also regulate various physiological processes in plants, such as leaf expansion and chloroplast development. Therefore, the application of cytokinins can effectively prevent plant tissues from senescing and promote overall plant growth and development.

Gibberellin is a plant hormone that promotes growth and development. It is known to break dormancy in seeds and buds by stimulating germination and sprouting. When gibberellin is applied, it signals the seed or bud to activate metabolic processes and resume growth. This hormone is responsible for elongation of stems, cell division, and fruit development. Therefore, the application of gibberellin can effectively break dormancy in seeds and buds.

The statement "All known growth regulators of plant activities are chemicals produced naturally in plants" is not true. While many plant hormones are indeed produced naturally in plants, there are also synthetic growth regulators that are used in agriculture and horticulture to manipulate plant growth and development. These synthetic growth regulators are not naturally produced by plants.

Root branching is not a physiological change related to photoperiodism. Photoperiodism refers to the response of plants to the duration of light and darkness in a day, which triggers specific physiological changes. Seed germination, breaking bud dormancy, flowering, and onset of senescence are all examples of physiological changes that can be influenced by photoperiodism. However, root branching is not directly regulated by photoperiod and is more influenced by other factors such as soil conditions and nutrient availability.