Plant Hormones Overview

Study Notes

Plant Hormones

Plant hormones, also known as phytohormones, are signaling molecules produced within plants, controlling various physiological processes.
They are produced in very small amounts but have profound effects on growth, development, and responses to environmental stresses.
Several major classes of plant hormones exist, each with diverse roles:
- Auxins: Promote cell elongation, involved in apical dominance, phototropism, and gravitropism. They are often produced in the shoot tips and transported downwards.
- Gibberellins: Stimulate stem elongation, flowering, and fruit development. They also play a crucial role in mobilization of food reserves during seed germination.
- Cytokinins: Promote cell division and differentiation, delay senescence (aging) in leaves and flowers, and are involved in apical dominance regulation. They are often produced in roots and transported upwards.
- Abscisic acid (ABA): Inhibits growth, regulates stomatal closure during water stress, and promotes seed dormancy. It's also involved in responses to various environmental stresses.
- Ethylene: Promotes fruit ripening, leaf abscission (falling), and senescence. It also plays a role in stress responses.
Plant hormones often interact in complex ways, modulating each other's effects. For instance, auxins and cytokinins are often antagonistic, influencing the balance between cell division and elongation.
Environmental factors significantly affect hormone production and actions, influencing plant growth and development in response to light, temperature, water availability, and nutrient levels.

Animal Hormones

Animal hormones are chemical messengers produced by endocrine glands, traveling through the bloodstream to target tissues to produce specific responses.
These hormones regulate a vast array of functions including metabolism, growth, reproduction, and homeostasis.
The major classes of animal hormones include:
- Steroid hormones: Derived from cholesterol, typically hydrophobic and can cross cell membranes. Examples include cortisol, estrogen, progesterone, and testosterone. They affect gene expression in target cells.
- Peptide hormones: Short chains of amino acids, typically hydrophilic and cannot cross cell membranes. They bind to receptors on cell surfaces, triggering intracellular signaling cascades. Examples are insulin, glucagon, and growth hormone.
- Amine hormones: Derived from amino acids like tyrosine. They can be either hydrophilic or lipophilic, depending on the specific hormone. Examples include epinephrine (adrenaline), norepinephrine, and thyroid hormones.
Hormone production is highly regulated, usually by negative feedback mechanisms. When a hormone's level rises, it triggers a response that reduces further production, ensuring homeostasis.
Endocrine glands like the pituitary, thyroid, adrenal, and gonads are crucial for hormone production and regulation.
Hormone receptors on target cells are highly specific, ensuring that only certain cells respond to particular hormones. Specific receptors determine the targets for hormone action.
Hormones are involved in complex interactions throughout the body, mediating communication between different organs and systems.
The actions of some hormones can be affected by other hormones in a synergistic or antagonistic manner; multiple hormones may work together for a full developmental response.
Hormonal imbalances can lead to various disorders, from metabolic problems to reproductive issues, highlighting the importance of precise hormonal regulation in animals.

Description

This quiz covers the essential roles and functions of plant hormones, also known as phytohormones. It delves into various classes such as auxins, gibberellins, cytokinins, and abscisic acid, highlighting their impact on plant growth and development. Test your knowledge on how these hormones affect physiological processes in plants.