Revision: 12th Std >> Plant Growth and Mineral Nutrition MAH-MHT CET (PCM/PCB) Plant Growth and Mineral Nutrition

Growth rate can be defined as increased plant growth per unit time.

Plant hormones are known as phytohormones. These are organic molecules that serve as mediators, similar to animal hormones, to facilitate the coordination of a variety of cellular activities within a plant.

A hormone is a chemical messenger produced in one part of an organism and transported to other parts, where it regulates growth, development, and responses.

Stimuli are the changes in the external or internal environment of an organism that trigger a response or movement.

Responses are the actions or movements shown by an organism as a result of the stimuli.

Parthenocarpy is the process by which fruits develop naturally or artificially without the necessity of fertilizing ovules, resulting in seedless fruits.

Parthenocarpic fruits are those that develop without fertilization. Auxins can induce such fruit formation in plants like apples, tomatoes, and bananas.

Parthenocarpy is the process of fruit development without fertilization.

In the majority of vascular plants, apical buds dominate over lateral buds. The growth of lateral buds occurs only after the removal of the apical buds. This phenomenon of the suppression of the growth of lateral buds by apical buds is called apical dominance.

Apical dominance is the phenomenon where the apical (terminal) bud of a plant suppresses the growth of lateral buds. This is mainly due to the action of auxins produced in the apical bud.

Gibberellin is a plant growth hormone found mainly in meristematic tissues like stem apex, root apex, buds, and seeds. It promotes internode elongation, breaks seed dormancy, and supports fruit development. Gibberellic acid (GA₃) is the most studied form of gibberellin.

Cytokinin is a plant hormone discovered in the 1950s by Skoog and Miller. It is primarily produced in root tips and transported via xylem. Cytokinin promotes plant growth by stimulating cell division, especially in germinating seeds, developing fruits, and embryos.

Abscisic acid is a plant hormone found in chloroplasts of leaves and in high amounts in fruits and seeds. It acts as a growth inhibitor and is present in angiosperms, gymnosperms, pteridophytes, and some mosses.

Abscission is the process by which plants shed or detach various portions that are no longer necessary for them, such as leaves, fruits, flowers, and seeds.

The response of plants to the relative length of light and dark periods with reference to the initiation of flowering is called photoperiodism.

The low-temperature treatment or chilling treatment of germinating seeds or seedlings to promote early flowering in plants is called vernalization. It was evidenced by Klippart (1918).

Chemoautotrophs are those who make their own food by deriving the energy from chemical reactions. e.g., Nitrifying bacteria, Iron bacteria etc.

1. Cytokinins promote plant growth by stimulating cell division, even in non-meristematic tissues.
2. They help expand cotyledons during seed development.
3. Cytokinins break seed dormancy and encourage germination.
4. They enhance chlorophyll synthesis and delay leaf senescence.
5. Cytokinins inhibit apical dominance, promoting lateral bud growth.

1. ABA is a growth-inhibiting hormone that slows down plant metabolism.
2. It induces seed dormancy and prevents germination under unfavorable conditions.
3. ABA promotes senescence and abscission of leaves, flowers, buds, and fruits.
4. It causes stomatal closure, helping the plant conserve water.
5. ABA enhances stress tolerance in plants, earning it the name "stress hormone."