What is the primary difference between plant growth and plant development?

Plant growth refers specifically to an irreversible increase in the size, mass, or volume of a plant or its parts, typically due to cell division, enlargement, and differentiation. It's a quantitative aspect. Plant development, however, is a much broader, qualitative term encompassing all the changes a plant undergoes throughout its life cycle, from germination to senescence. This includes growth, differentiation, organ formation, flowering, fruiting, and aging. So, growth is a component of development, but development includes many other complex processes beyond just an increase in size.

How do plant growth regulators (PGRs) differ from animal hormones?

While both PGRs and animal hormones are chemical messengers, they have key differences. PGRs are generally simpler molecules, often acting at their site of production or transported over short distances, and their effects are often pleiotropic (multiple effects) and concentration-dependent. Animal hormones are typically more complex, produced in specialized endocrine glands, transported via the bloodstream, and usually have more specific target organs and effects. Plants also lack a dedicated endocrine system like animals.

Explain the concept of developmental plasticity with an example.

Developmental plasticity is the ability of a plant to alter its developmental pathway in response to environmental cues. This means the same plant can show different forms or structures depending on the conditions it experiences. A classic example is heterophylly, seen in plants like cotton, coriander, and larkspur. Their juvenile leaves have a different shape compared to their mature leaves. Another example is the buttercup (*Ranunculus fluitans*), where submerged leaves are highly dissected, while emergent leaves are broad and lobed, adapting to different aquatic and aerial environments.

What is the 'stress hormone' in plants and why is it called so?

Abscisic Acid (ABA) is often referred to as the 'stress hormone' in plants. It earns this name because its production increases significantly under various environmental stresses, particularly water stress (drought). ABA plays a crucial role in helping the plant cope with these adverse conditions, primarily by inducing stomatal closure to reduce water loss through transpiration and by promoting dormancy in seeds and buds, allowing the plant to survive unfavorable periods.

What is the critical photoperiod in the context of photoperiodism?

The critical photoperiod is a specific duration of light (or darkness) that must be exceeded or fallen short of for a plant to flower. It's not necessarily 12 hours. For short-day plants (SDPs), flowering occurs when the photoperiod is *shorter* than their critical photoperiod. For long-day plants (LDPs), flowering occurs when the photoperiod is *longer* than their critical photoperiod. It's a threshold, not a fixed duration, and the actual length varies greatly among different plant species.

How does ethylene promote fruit ripening, and what kind of fruits are most affected?

Ethylene is a gaseous plant hormone that plays a crucial role in fruit ripening, particularly in 'climacteric' fruits. It promotes ripening by stimulating the synthesis of enzymes that break down cell walls (softening), convert starches to sugars (sweetening), and produce volatile compounds (aroma). It also increases the respiration rate, a phenomenon known as the climacteric rise. Climacteric fruits, such as apples, bananas, mangoes, and tomatoes, show a sharp increase in respiration and ethylene production during ripening, and can ripen after being harvested.

Plant Growth and Development

Biology

NEET UG

Version 1Updated 21 Mar 2026

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Plant growth and development encompass all the progressive, irreversible changes that a plant undergoes throughout its life cycle, from seed germination to senescence and death. Growth is fundamentally an irreversible increase in size, mass, or volume, resulting from cell division, cell enlargement, and cell differentiation. Development, a broader term, includes growth, differentiation, and all ot…

Quick Summary

Plant growth is an irreversible increase in size or mass, driven by cell division, enlargement, and differentiation, primarily occurring in meristematic regions. Development encompasses the entire life cycle, including growth, organ formation, flowering, and senescence.

Growth can follow arithmetic (linear) or geometric (sigmoid) patterns, influenced by water, oxygen, nutrients, temperature, and light. Plants exhibit plasticity, adapting their development to environmental cues.

Key regulators are Plant Growth Regulators (PGRs): Auxins, Gibberellins, and Cytokinins promote growth, while Abscisic Acid (ABA) and Ethylene generally inhibit growth or promote senescence/ripening. Auxins promote cell elongation and root initiation; Gibberellins cause stem elongation and break dormancy; Cytokinins promote cell division and delay aging.

ABA induces dormancy and stomatal closure; Ethylene promotes fruit ripening and abscission. Photoperiodism (response to day/night length) and vernalization (cold requirement for flowering) are crucial environmental controls over flowering.

Seed dormancy, a state of suspended growth, can be overcome by various physical or chemical treatments.

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Key Concepts

Auxins: Roles and Applications

Auxins are a class of plant hormones primarily known for promoting cell elongation in stems and coleoptiles.…

Gibberellins: Stem Elongation and Dormancy Breaking

Gibberellins are a large group of PGRs, with GA3 being the most studied. Their most striking effect is…

Photoperiodism: Classification and Mechanism

Photoperiodism is the physiological response of plants to the relative lengths of day and night, primarily…

Growth: — Irreversible increase in size/mass.

Development: — Entire life cycle changes.

PGRs: — Auxins, Gibberellins, Cytokinins (Promoters); ABA, Ethylene (Inhibitors).

Auxin: — Apical dominance, rooting, parthenocarpy, 2,4-D (herbicide).

Gibberellin: — Stem elongation (bolting), breaks dormancy, fruit size (

GA_3

Cytokinin: — Cell division, lateral bud growth, delays senescence.

ABA: — Stress hormone, stomatal closure, seed dormancy, abscission.

Ethylene: — Gaseous, fruit ripening, senescence, abscission.

Photoperiodism: — Response to day/night length (SDP, LDP, DNP).

Vernalization: — Cold treatment for flowering.

Growth Curves: — Arithmetic (linear), Geometric (sigmoid).

Plasticity: — Developmental changes due to environment (e.g., heterophylly).

All Good Crops Always Emerge:

Auxins: Apical dominance, Allongation, Adventitious roots.

Gibberellins: Giant growth (stem elongation), Germination, Grape enlargement.

Cytokinins: Cell division, Cytokinesis, Counteract apical dominance.

Abscisic Acid (ABA): Absent growth (dormancy), Absolute stress (stomatal closure), Abscission.

Ethylene: Excellent ripening, Early senescence, Elongation (deep water rice).