Plant Growth and Development: questions with answers

A lateral cambium adds cells in a radial pattern for secondary growth. Plant growth is open because particular meristems retain division capacity; this does not mean that every differentiated organ grows indefinitely.

Root and shoot apical meristems chiefly add primary length along an axis, whereas vascular and cork cambia add secondary girth. Open growth refers to persistent division in selected meristems, while many daughter cells differentiate and lose division capacity.

The greatest increase in spacing identifies the elongation zone immediately behind the apical meristem. The meristem supplies new cells by division; elongation produces greatest extension, and maturation farther away brings wall thickening and specialisation.

From the growing root tip toward the older root, the meristematic region supplies new cells by division, the elongation region increases length mainly through cell enlargement, and the maturation region develops specialised cells. The region with the most active division is therefore not the same as the region with the greatest extension.

Only one daughter retains division capacity at each arithmetic division; the other differentiates. This division rule links daughter-cell fate with additive or multiplicative growth.

Natural resource limitation changes the trajectory from lag through a steep exponential region to a stationary plateau. Curve shape reflects whether increase remains constant, accelerates under ideal conditions, or slows as resources become limiting.

The first claim confuses a rate with a size and omits both starting value and elapsed time. The second drops the required multiplier $W_0$; the exponential factor must be applied to the initial size.

Use the stated position, rather than shared meristematic origin alone.

Tip-facing displacement toward the cap can direct root-cap fate; peripheral displacement can direct epidermal fate.

Its peripheral position can direct it toward an epidermal fate. This positional dependence is called open differentiation.

Differentiation is maturation into a specialised state, commonly after the cell loses division capacity. In tracheary elements, loss of protoplasm and lignocellulosic wall development are directly suited to water conduction under tension.

The difference is phase-dependent heterophylly. This illustrates plasticity: a plant can follow different developmental pathways in response to its life phase or its environment. PGRs are intrinsic intercellular chemical controls, even though extrinsic conditions may act through them.

Genetic factors and intercellular chemicals such as PGRs are intrinsic controls. Light, temperature, water, oxygen, nutrition and gravity are extrinsic controls; an extrinsic factor may act through a PGR without turning the PGR itself into an external factor. Plasticity may reflect life phase or environment.

The coleoptile tip senses unilateral light and supplies a transmissible influence that causes bending below; the bending region is not the source. The Darwins located this influence, while Went later isolated auxin. Kinetin was obtained from autoclaved herring-sperm DNA and is not naturally present in plants; zeatin is a natural cytokinin.

IAA is an indole compound, kinetin an adenine derivative, ABA a carotenoid derivative, GA3 a terpene and ethylene a gas. Auxins, gibberellins and cytokinins are chiefly promoters, ABA is chiefly inhibitory, and ethylene can fit either group but is largely inhibitory; these are not rigid chemical or functional equivalences.

Removing the apical bud releases lateral buds because the growing apex normally suppresses their growth. Auxin prevents early fruit drop but promotes abscission of an older mature fruit. Gibberellins promote stem elongation and bolting.

Ethylene breaks seed and bud dormancy, whereas ABA induces dormancy and inhibits germination. ABA promotes stomatal closure under stress. PGR effects can overlap or interact: for example, more than one regulator can influence dormancy, senescence, abscission or apical dominance.