How do Auxin and Cytokinin dynamically interact to regulate apical dominance?

Apical dominance is enforced by high concentrations of auxin synthesized at the shoot apical meristem, which migrates basipetally to inhibit lateral bud growth. Cytokinin synthesized in root tips travels acropetally to promote lateral shoot growth. Decapitation of the shoot apex reduces auxin levels, enabling cytokinin to override inhibition and induce lateral branching.

Why is Abscisic Acid ($\text{ABA}$) categorized as a stress hormone during water deficit conditions?

When water potential drops ($\Psi_w \ll 0$), roots signal rapid synthesis of $\text{ABA}$ in vascular tissues. $\text{ABA}$ binds to receptors on guard cells, activating plasma membrane channel efflux of $\text{K}^+$ and anions $\text{Cl}^-$. Loss of osmotic solutes lowers intracellular turgor pressure ($\Psi_p \rightarrow 0$), causing guard cell flaccidity and instantaneous stomatal closure to limit transpirational loss.

What is the most effective approach to memorize Plant Growth Regulator (PGR) functions for NEET?

Map each hormone directly to its primary physiological trigger: Auxin $\rightarrow$ apical dominance and cell elongation; Gibberellins $\rightarrow$ bolting and $\alpha$-amylase induction; Cytokinins $\rightarrow$ cytokinesis and delaying leaf senescence; Ethylene $\rightarrow$ fruit ripening and triple response; $\text{ABA}$ $\rightarrow$ stomatal closure and seed dormancy.

Plant Growth and Development Notes, Formulas, Traps & PYQs | ExamiFly

Beta

Please wait while we prepare everything for you

Plant Growth and Development Notes, Formulas, Traps & PYQs | ExamiFly | Examifly

Solved High-Yield Sample Questions

Practice Mode

Question #1NEET 2024

A plant organ undergoes geometric growth where initial biomass $W_0 = 10\text{ g}$ expands to $W_1 = 10 e^{2}\text{ g}$ over a duration of $t = 4\text{ days}$ . Calculate the relative growth rate $r$ in $\text{day}^{-1}$ .

Solution Locked

Step-by-Step Solution & Concept

Step 1

Write down the governing exponential growth equation $W_1 = W_0 e^{rt}$ .

Step 2

Substitute given parameters $W_1 = 10 e^{2}\text{ g}$ , $W_0 = 10\text{ g}$ , and $t = 4\text{ days}$ to obtain $10 e^{2} = 10 e^{4r}$ .

Step 3

Simplify by canceling $10$ and equating exponents $4r = 2$ , yielding $r = \frac{2}{4} = 0.50\text{ day}^{-1}$ .

Select an option & click Check Answer to reveal solution

Question #2NEET 2023

Two leaves $A$ and $B$ with initial surface areas $A_0 = 5\text{ cm}^2$ and $B_0 = 50\text{ cm}^2$ expand to $10\text{ cm}^2$ and $55\text{ cm}^2$ respectively in time interval $\Delta t$ . Compare their Absolute Growth Rates ( $AGR$ ) and Relative Growth Rates ( $RGR$ ).

Solution Locked

Step-by-Step Solution & Concept

Step 1

Calculate $AGR = \frac{\Delta A}{\Delta t}$ . For leaf $A$ , $\Delta A = 10 - 5 = 5\text{ cm}^2$ . For leaf $B$ , $\Delta A = 55 - 50 = 5\text{ cm}^2$ . Hence, $AGR_A = AGR_B = \frac{5}{\Delta t}$ .

Step 2

Calculate $RGR = \frac{\Delta A}{A_0 \cdot \Delta t}$ . For leaf $A$ , $RGR_A = \frac{5}{5 \cdot \Delta t} = \frac{1}{\Delta t}$ . For leaf $B$ , $RGR_B = \frac{5}{50 \cdot \Delta t} = \frac{0.1}{\Delta t}$ .

Step 3

Compare values: $AGR_A = AGR_B$ and $RGR_A > RGR_B$ because $\frac{1}{\Delta t} > \frac{0.1}{\Delta t}$ .

Select an option & click Check Answer to reveal solution

If you want to explore more chapters of Biology then:

Click Here

Mastering Plant Growth and Development: Formulas, Traps & Exam Strategy | ExamiFly

Chapter Overview

Core Subtopics & Syllabus Breakdown

Key Formulas & High-Yield Equations

Arithmetic Growth Kinetics

Geometric Growth Rate

Absolute Growth Rate (AGR)

Relative Growth Rate (RGR)

Cell Turgor Expansion Model

Common Mistakes & Traps to Avoid

Past Year Question (PYQ) Trends

Solved High-Yield Sample Questions

Frequently Asked Questions

Master Plant Growth and Development with 250+ Curated NEET Drills & AI Error-Correction