Plant Growth and Development: NEET previous year questions

The elongation phase is characterised by increased vacuolation, cell enlargement and deposition of new cell wall material. A large, conspicuous nucleus with dense cytoplasm is a feature of the meristematic (dividing) phase, not the elongation phase, so it is the exception.

2,4-dichlorophenoxyacetic acid (2,4-D) is a synthetic auxin used as a selective herbicide against dicot weeds (P - III).
GA$_3$ is used in the malting/brewing industry to speed up the process (Q-I).
Kinetin, a cytokinin, promotes nutrient mobilisation and delays senescence (R-IV).
Abscisic acid (ABA),
the stress hormone, promotes stomatal closure during water stress (S-II).
Hence P-III, Q-I, R-IV, S-II.

Plasticity is the ability of plants to follow different developmental pathways and form different structures in response to environment or life phase; heterophylly in cotton, coriander and larkspur is a classic example. Dedifferentiation and redifferentiation describe changes in the meristematic state of cells, and elasticity is not the relevant developmental term.

2,4-dichlorophenoxyacetic acid is a synthetic auxin widely used to kill dicotyledonous weeds while leaving mature monocotyledonous crops such as wheat and rice largely unharmed. At herbicidal concentrations it forces uncontrolled, disorganised growth in susceptible plants. NCERT Class 11, Plant Growth and Development.

The dramatic elongation of the internodes just before flowering is called BOLTING, and it is the classic gibberellin response in rosette plants such as cabbage and beet. Applying gibberellin causes the compressed rosette to shoot upward into a tall flowering stalk. NCERT Class 11, Plant Growth and Development.

Arithmetic growth adds a CONSTANT amount per unit time, described by $L_t = L_0 + rt$. Substituting, $L_7 = 20 + (30 \times 7) = 230\ \text{cm}$. The contrast worth holding onto is with geometric growth, where the increment itself grows and the curve is exponential rather than a straight line. NCERT Class 11, Plant Growth and Development.

Gibberellic acid is a plant hormone that promotes seed germination, not dormancy. Abscisic acid, phenolic acid, and para-ascorbic acid are known to inhibit seed germination and maintain dormancy. Chapter: Plant Growth and Development.

Gibberellins, when sprayed on sugarcane, promote stem elongation and increase the yield. Chapter: Plant Growth and Development.

The process of growth is maximum during the log phase, when cells divide rapidly and the population increases exponentially. Chapter: Plant Growth and Development.