Hormones

Auxins are a class of plant hormones that play a crucial role in coordinating various growth and behavioral processes in the plant's life cycle. They are essential for the regulation of plant growth by influencing cell elongation, root growth, and differentiation.

The question asks us to identify which of the given substances are auxins. Let's evaluate each option:

• 1-Naphthaleneacetic acid (NAA): NAA is a synthetic auxin used predominantly as a growth regulator. It promotes root development and is often used in agriculture and horticulture to encourage plant growth.
• Indole-3-butyric acid (IBA): IBA is a naturally occurring auxin that is involved in root elongation and cell enlargement. It is widely used in plant propagation.
• 2,4-Dichlorophenoxyacetic acid (2,4-D): 2,4-D is a synthetic auxin commonly used as a herbicide. It mimics the natural auxin activity and causes uncontrolled growth, eventually leading to the death of unwanted plants.
• Indole-3-acetic acid (IAA): IAA is the most prominent and naturally predominant auxin in plants. It plays a significant role in virtually all developmental processes, including cell division, elongation, and differentiation.

All the substances listed are recognized as auxins. They either naturally occur in plants or are synthetic compounds that mimic the behavior of natural auxins by inducing similar physiological responses in plants.

Therefore, the correct answer is:

• 1-Naphthaleneacetic acid
• Indole-3-butyric acid
• 2,4-Dichlorophenoxyacetic acid
• Indole-3-acetic acid

Each of these fulfilling roles associated with auxins makes them integral in plant growth and development processes.

The question asks which hormones act as wound hormones in plants. Wound hormones are substances that respond to injury in plants and help in their repair. Let's analyze each given option:

1. Ethylene:
   Ethylene is a gaseous plant hormone known for its role in the ripening of fruits. Besides that, it also plays a critical role in the response to mechanical stress and is involved in wound healing. It helps coordinate the repair process by inducing rapid synthesis of related enzymes and compounds.
2. Cytokinins:
   Cytokinins are essential for cell division and shoot initiation. They are also involved in responses to plant injury, particularly by promoting cell division at wound sites, facilitating the formation of new cells to replace damaged ones.
3. Abscisic Acid (ABA):
   ABA is primarily known for its role in stress responses, especially drought and salinity. However, it also has a role in the plant's response to wounding. ABA can mediate the signal transduction pathways that lead to wound healing and the production of defensive compounds.
4. Dextrin:
   Dextrins are a group of carbohydrates, specifically polysaccharides, and they do not function as hormones in plants. They are not involved in the wound healing process in plants.

Based on the above explanations, the correct answer is: Ethylene, Cytokinins, and Abscisic Acid are the hormones that act as wound hormones in plants as they play a significant role in the repair and response to plant wounds.

To understand which hormone elicits the 'triple response' in a germinating seedling encountering an underground obstacle, we need to explore the characteristics of plant hormones.

The 'triple response' is a growth maneuver that helps a seedling navigate around obstacles in the soil. This response is characterized by three main changes in the plant's growth pattern:

1. Reduction in elongation: The elongation of the stem is reduced, which allows the plant to conserve its energy and resources when it faces resistance from the soil.
2. Radial swelling: The stem swells, or becomes thicker, which increases its mechanical strength and helps push through the soil.
3. Horizontal growth: The direction of the stem growth changes from vertical to horizontal, helping the seedling grow around the obstacle.

Among the given options, ethylene is the hormone known for inducing the 'triple response.' Ethylene is a gaseous plant hormone involved in various processes such as fruit ripening, leaf abscission, and responses to mechanical stress.

Let's rule out the other options provided:

• Auxin: Primarily involved in cell elongation and growth. It helps with the directional growth of the plant towards light (phototropism) or against gravity (gravitropism).
• Cytokinin: Promotes cell division and is involved in various growth and differentiation processes but does not induce a 'triple response.'
• Gibberellins: Primarily promote stem elongation, seed germination, and flowering, rather than inducing a restraining response like the 'triple response.'

Thus, the correct answer to the question is Ethylene.