Comprehensive Study Notes on Hormones, Enzymes, and Physiological Coordination

Distinguishing Features Between Hormones and Enzymes

Hormones and enzymes are both vital components of biological regulation and catalysis, yet they possess distinct characteristics regarding their origins, chemical compositions, and mechanisms of action. One of the primary differences lies in their source: hormones are synthesized and secreted by endocrine glands and specialized clusters of secretory cells, whereas enzymes are produced by exocrine glands and glandular epithelium cells.

Chemically, hormones exhibit a diverse range of compositions, being made up of proteins, polypeptides, glycoproteins, or steroids. In contrast, enzymes are almost exclusively made up of protein. Their target locations also vary significantly; hormones usually exert their effects on target organs located away from their source of origin, while enzymes may operate either at the site of origin or further away.

A key functional difference is their reusability. Once a hormone has performed its specific regulatory function, it is generally considered absent for reuse (it denatures), whereas enzymes remain present and can be reused to catalyze further reactions. The quantity required for biological activity is also a point of distinction: hormones are required in very little amounts to be effective, while enzymes are needed in comparatively larger quantities, and their rate of action increases proportionately with an increase in quantity, up to a certain limit.

In terms of function, hormones act by stimulating the secretion of other glands and controlling various biochemical reactions and physiological activities. Enzymes, on the other hand, function strictly as catalysts for all biochemical reactions, speeding up processes without being consumed in the reaction itself.

Salient Features and Characteristics of Phytohormones

Phytohormones, or plant hormones, possess several salient features that govern how they regulate plant growth and development. The source of these hormones is primarily the meristematic tissues located in the apical regions of stems and roots, as well as tender leaves, the plumule, the radical, and other actively growing tissues.

The nature of transportation for phytohormones is highly efficient. They can act either close to their source or at a distance, transported to various target tissues through intercellular diffusion or through the vascular tissues, namely the xylem and phloem. This movement allows the plant to coordinate growth across different organs.

Phytohormones perform a wide range of functions, including the regulation of apical and lateral buds, the blooming of flowers, and the formation of fruits and seeds. They are also essential for the germination of seeds, the process of budding, sensitivity to environmental stimuli, and the delay of senescence (the aging of plant parts).

The fate of phytohormones is to denature once their physiological functions are completed. They are broken down by specific enzymes or other environmental factors. For instance, auxin is denatured by exposure to bright light and the action of the indole acetic acid oxidase enzyme. Similarly, gibberellin and cytokinin are disintegrated by their respective enzymes, gibberellin oxidase and cytokinin oxidase.

Common Functions of Phytohormones in Plant Physiology

Phytohormones are instrumental in regulating several key physiological activities within a plant. One major function is the promotion of apical and lateral growth. Primary growth occurs at the apex of the stem and root, making the shoot taller and the roots longer. Lateral growth occurs through the lateral meristem, making the plant body wider. In both instances, phytohormones instigate cell division in these growing regions.

The blooming of flowers, which are the reproductive organs of the plant, is also controlled by hormones. Flowers develop from floral buds, and phytohormones play a vital role in both the development of these buds and the eventual blooming of the flowers. Furthermore, phytohormones are responsible for caulogenesis and rhizogenesis, which refer to the formation of the stem from the plumule and the root from the radical, respectively.

Seed germination is another process regulated by these chemicals. Seeds often remain dormant for a period after formation, but in the presence of specific external and internal factors, phytohormones activate enzymes and enhance the supply of food to the embryo, allowing the seed to break dormancy and germinate.

Lastly, phytohormones regulate tropic movements, which are growth-related movements of curvature. These include phototropic movements (growth in response to light) and geotropic movements (growth in response to gravity), ensuring the plant orientates itself correctly in its environment.

Coordination Systems: Endocrine Versus Nervous System

Animals possess two primary systems for internal coordination: the endocrine system and the nervous system. There are significant similarities between the two, as both act as mediums of coordination within the animal body, both help maintain homeostasis (stable internal conditions), and both are regulated via feedback mechanisms.

However, there are stark dissimilarities in their features. The speed of action in the endocrine system is relatively slow, while the nervous system is very fast. The durability of action also differs; the endocrine system provides long-lasting effects, whereas the nervous system's effects are momentary. In the endocrine system, the chemical substance (hormone) denatures as the function is completed, while in the nervous system, the tissue remains unchanged after the function is performed.

Furthermore, while the endocrine system occurs in both animals and plants, the nervous system is found only in animals. The nature of these systems is also fundamentally different: the endocrine system is composed of chemical substances, while the nervous system is a tissue made up of specialized types of cells.

Comparative Analysis of Adrenaline and Nor-adrenaline

Adrenaline and nor-adrenaline are two related hormones with specific physiological effects, particularly regarding the cardiovascular system and metabolism. Adrenaline increases the heart rate more significantly than nor-adrenaline. Regarding blood pressure, both hormones increase systolic pressure, but nor-adrenaline also increases diastolic pressure, whereas adrenaline has no visible effect on diastolic pressure. Adrenaline increases cardiac output, while nor-adrenaline shows no visible effect on this metric.

In terms of metabolism, both hormones increase blood sugar levels and the release of free fatty acids. However, their effects on blood vessels differ; adrenaline increases the contractibility of most arterial walls but decreases the contractibility of arterial walls in the heart, skeletal muscles, and liver. Nor-adrenaline, conversely, increases the contractibility of smooth muscles across blood vessels generally.

Both hormones act to quicken breathing. A final point of distinction is their effect on blood counts: adrenaline increases the eosinophil count, whereas nor-adrenaline has no effect on the eosinophil count.