Plant Responses and Hormonal Regulation

Definition: Growth responses of plants to environmental stimuli.
Types:
- Phototropism: Growth towards light (positive) or away (negative).
- Gravitropism: Growth in response to gravity; roots exhibit positive gravitropism, while shoots exhibit negative gravitropism.
- Thigmotropism: Growth in response to touch; common in climbing plants.
- Hydrotropism: Growth towards moisture.

Definition: Plant response to the length of day and night.
Types:
- Short-day plants: Flower when days are shorter than a critical length (e.g., chrysanthemums).
- Long-day plants: Flower when days are longer than a critical length (e.g., spinach).
- Day-neutral plants: Flower regardless of day length (e.g., dandelions).
Key Mechanism: Involves phytochromes, pigments that detect light changes.

Plant Hormones:
- Auxins: Promote cell elongation and phototropism.
- Gibberellins: Stimulate seed germination and stem elongation.
- Cytokinins: Promote cell division and delay aging.
- Abscisic Acid: Induces dormancy and stress responses (e.g., drought).
- Ethylene: Regulates fruit ripening and leaf abscission.
Role of Hormones: Coordinate growth, development, and responses to environmental changes.

Definition: Actions organisms take to increase survival and reproduction.
Examples:
- Migration: Seasonal movement to exploit resources (e.g., birds migrating south for winter).
- Hibernation: Period of inactivity to conserve energy during harsh conditions.
- Mating behaviors: Rituals or displays to attract mates.
- Social behaviors: Group living for protection or resource sharing (e.g., herding in animals).

Types:
- Physical defenses: Thorns, spines, and tough leaves in plants; shells and armor in animals.
- Chemical defenses: Production of toxins or repellents (e.g., alkaloids in plants, venom in snakes).
- Behavioral defenses: Camouflage, mimicry, and flight responses in animals.
- Induced defenses: Responses triggered by herbivory or predation (e.g., increased toxin production after being eaten).

Growth responses of plants to environmental stimuli.
Phototropism: Movement towards light is positive, while movement away from light is negative.
Gravitropism: Roots demonstrate positive gravitropism (growth toward gravity), whereas shoots show negative gravitropism (growth away from gravity).
Thigmotropism: Response to touch, often observed in climbing plants as they wrap around supports.
Hydrotropism: Growth directed towards moisture sources, helping plants access water.

Plant response influenced by the duration of daylight and darkness.
Short-day plants: Flower when day length is shorter than a specific duration; examples include chrysanthemums.
Long-day plants: Bloom when day length exceeds a critical period; spinach is a notable example.
Day-neutral plants: Flower based on other factors, with no reliance on day length; dandelions are included in this category.
Phytochromes, which are light-detecting pigments, play a crucial role in this process.

Plant growth and responses are regulated by various hormones.
Auxins: Enhance cell elongation and are key to phototropic responses.
Gibberellins: Trigger processes like seed germination and stem growth.
Cytokinins: Encourage cell division and help delay aging in plants.
Abscisic Acid: Causes dormancy and mediates stress responses, such as drought conditions.
Ethylene: A hormone involved in the ripening of fruit and the shedding of leaves.
Hormones collectively assist in navigating growth, development, and environmental adaptations.

Actions taken by organisms to enhance survival and reproductive success are termed behavioral adaptations.
Migration: Seasonal relocations to maximize resource availability, exemplified by birds migrating south for winter.
Hibernation: A dormant state to conserve energy throughout unfavorable conditions.
Mating behaviors: Ritualistic displays or actions designed to attract potential mates.
Social behaviors: Group living strategies for increased protection or resource sharing, as seen in herding behaviors of certain animals.

Defense strategies utilized by organisms to protect against threats.
Physical defenses: Structural adaptations such as thorns and spines in plants or shells and armor in animals.
Chemical defenses: Synthesis of toxic substances or repellents, including plant alkaloids and animal venoms.
Behavioral defenses: Mechanisms like camouflage, mimicry, and evasive movements observed in various species.
Induced defenses: Defensive responses stimulated by predation or herbivory, leading to increased toxin production post-damage.