Development — Plasticity

NCERT grounding

The primary source for this subtopic is NCERT Class XI Biology, Chapter 13 — Plant Growth and Development, Section 13.3 (Development). The text reads:

"Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence... Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity."

The NCERT summary reinforces the relationship: "Since differentiation in plants is open, the development could also be flexible, i.e., the development is the sum of growth and differentiation. Plant exhibit plasticity in development." This paragraph is the conceptual anchor that NEET questions are built around.

Development — defined

Development is the comprehensive term for all changes — structural, functional, and physiological — that a plant undergoes from the germination of the seed to the senescence and death of the organism. It is not a single event but a continuous, ordered succession of processes.

NCERT defines development as the sum of two component processes: growth (an irreversible, permanent increase in size) and differentiation (structural and functional specialisation of cells). Neither process alone constitutes development — it is their integration over the entire life of the plant.

Because differentiation in plants is open (cells/tissues arising from the same meristem may differentiate differently depending on position or external signals), development is inherently flexible. A cell positioned away from the root apical meristem differentiates as a root-cap cell; one pushed to the periphery matures as epidermis — same meristematic origin, different developmental fate.

Plasticity in development

Plasticity is the ability of plants to follow different developmental pathways in response to the environment or to the phase of life, resulting in structurally different organs from the same genetic blueprint. It is the visible consequence of open differentiation operating under variable intrinsic and extrinsic signals.

Plasticity is not random variation — it is a programmed, reversible or irreversible response to specific signals. The same genotype produces phenotypically distinct organs because gene expression is modulated by the developmental context. This is why plasticity is classified as a feature of open development rather than of genetic variability.

Heterophylly — two modes in detail

Phase-dependent heterophylly: cotton, coriander and larkspur

In plants such as cotton (Gossypium), coriander (Coriandrum sativum), and larkspur (Delphinium), the leaves produced during the juvenile phase of the plant's life are morphologically distinct from those produced in the adult phase. Juvenile leaves tend to be simpler, less-lobed, or differently shaped; adult leaves are more elaborately divided or compound. Both leaf types are generated by the same shoot apical meristem operating on identical genetic instructions — the difference arises from internal developmental cues tied to the plant's age and hormonal status.

This form of heterophylly is termed heterophyllous development due to phase of life in NCERT. It demonstrates that the developmental programme is not fixed at the cellular level but continues to be modulated by intracellular (genetic) and intercellular (hormonal) signals throughout the plant's life.

Environment-dependent heterophylly: Ranunculus (buttercup)

Ranunculus aquatilis (water buttercup) is the canonical NCERT example of environment-dependent plasticity. A single plant growing at the air–water interface produces two structurally distinct leaf types simultaneously:

The functional rationale is straightforward: in the aquatic medium, a broad lamina would create excessive drag and be torn apart by water currents. Dissected, ribbon-like leaves offer minimal resistance while maximising the surface area available for diffusion. The plant achieves this by deploying the same genome in two different transcriptional contexts — the physical properties of water versus air alter the hormonal and mechanical signals received by developing leaf primordia.

Tissue culture as experimental evidence for plasticity

Plant tissue culture provides an experimentally controlled demonstration of plasticity. When a callus — a mass of undifferentiated cells derived from a single explant — is placed on a nutrient medium supplemented with plant growth regulators, its developmental fate is determined by the ratio of auxin to cytokinin:

The same undifferentiated tissue, with the same genetic material, gives rise to morphologically and functionally opposite structures — roots versus shoots — purely as a function of the extrinsic hormonal signal in the medium. This is plasticity under controlled laboratory conditions, and it underscores that the genome contains the instructions for all developmental pathways simultaneously; which pathway is activated depends on the regulatory environment.

Controlling factors of development

NCERT states explicitly: "Development in plants (i.e., both growth and differentiation) is under the control of intrinsic and extrinsic factors." These two categories of control are complementary, not competing.

The interaction between intrinsic and extrinsic control is not incidental — it is the mechanistic basis for plasticity itself. The genome does not rigidly specify a single developmental outcome; it specifies a set of conditional responses. Environmental signals — mediated through PGRs and other signalling molecules — select among these conditional programmes. The result is a plant that can produce structurally distinct organs from a single genotype, optimised for the particular environmental context.

Worked examples

Common confusion & NEET traps