Plant Growth and Development — Class 11 MCQs with Answers

Plant Growth and Development — important questions & MCQs with answers (Class 11 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Auxin promotes:

   ASenescenceBCell elongation and apical dominanceCStomatal closureDDormancy
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   Answer: Cell elongation and apical dominance

   Explanation: Auxin drives cell elongation via acid growth and enforces apical dominance by suppressing lateral buds; cytokinin does the opposite, releasing those buds to grow.

2. Q2 of 6Easy

   Growth in plants is best defined as:

   ACell division onlyBReversible swelling of cellsCIncrease in dry weight onlyDIrreversible permanent increase in size of an organ
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   Answer: Irreversible permanent increase in size of an organ

   Explanation: Growth is an irreversible, permanent increase in size of a cell, organ or organism, driven by cell division and cell enlargement, unlike reversible swelling, which is not true growth.

3. Q3 of 6Medium

   Sigmoid (S-shaped) growth curve has:

   ANo patternBOnly one phaseCTwo phasesDLag, log (exponential), stationary phases
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   Answer: Lag, log (exponential), stationary phases

   Explanation: The sigmoid curve traces lag phase (slow start), log phase (fastest exponential growth) and stationary phase (growth plateaus); arithmetic growth instead gives a straight line, not this curve.

4. Q4 of 6Medium

   Cytokinins promote:

   ACell elongation onlyBCell divisionCSenescenceDWilting
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   Answer: Cell division

   Explanation: Cytokinins, derived from adenine, drive cytokinesis and cell division, and also delay senescence, the opposite effect of ethylene, which accelerates leaf and fruit ageing.

5. Q5 of 6Hard

   Assertion: Plants exhibit indeterminate growth. Reason: Meristems are present at specific locations throughout life.

   ABoth falseBBoth true but Reason does not explainCAssertion true, Reason falseDBoth true and Reason explains Assertion
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   Answer: Both true and Reason explains Assertion

   Explanation: Both statements are true and the reason explains the assertion: persistent meristems at root and shoot apices are exactly what let plants keep adding new tissue and grow indeterminately throughout life.

6. Q6 of 6Hard

   Photoperiodism affects:

   AFlowering response to day lengthBPhotosynthesis rateCRoot colourDSoil pH
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   Answer: Flowering response to day length

   Explanation: Photoperiodism is the flowering response to relative day and night length: short-day plants flower once uninterrupted night exceeds a critical duration, long-day plants when it falls short.

Plant Growth and Development notes: key concepts (Class 11 Biology)

Plants grow throughout life at their meristems and develop through cell division, enlargement and differentiation. This chapter defines growth phases and rates, then examines five plant growth regulators — auxins, gibberellins, cytokinins, abscisic acid and ethylene — and the light and cold cues, photoperiodism and vernalisation, that trigger flowering.

Growth

An irreversible, permanent increase in size, mass or cell number by division and enlargement; plant growth is indeterminate as meristems keep it going lifelong.

Phases of growth

Three overlapping phases: meristematic (cells divide), elongation (cells enlarge and vacuolate) and maturation (cells differentiate to their final form and function).

Growth rate

Increase per unit time; arithmetic growth gives a linear rate, while geometric growth is exponential, producing an overall S-shaped sigmoid growth curve.

Differentiation

Cells from meristems mature and specialise, often losing protoplasm and thickening walls to perform set jobs, as tracheids do for water conduction.

Dedifferentiation & redifferentiation

Mature cells can regain the power to divide (dedifferentiation, e.g. cork cambium) and then mature again into new cell types (redifferentiation).

Development

The sum of all changes an organism passes through in its life cycle, from seed germination to senescence, governed by intrinsic and extrinsic factors.

Auxins

IAA promotes cell elongation, apical dominance and rooting; it is used to stop fruit and leaf drop, induce parthenocarpy, and 2,4-D acts as a herbicide.

Gibberellins

GA₃ causes stem and internode elongation and bolting in rosette plants, breaks seed and bud dormancy, and speeds malting in the brewing industry.

Cytokinins

Promote cell division (cytokinesis), help break apical dominance, delay leaf senescence (Richmond-Lang effect) and aid nutrient mobilisation to leaves.

Abscisic acid

The 'stress hormone' inhibits growth, closes stomata under water stress, promotes seed dormancy and abscission, and antagonises the gibberellins.

Ethylene

A gaseous regulator that ripens fruit, promotes senescence and abscission, breaks dormancy and triggers epinasty; used to hasten ripening in storage and transit.

Photoperiodism

Flowering response to day and night length; short-day, long-day and day-neutral plants exist, with the critical dark period sensed by leaves via phytochrome.

Vernalisation

The promotion of flowering by a spell of low temperature; it blocks premature flowering and lets plants like winter wheat flower after cold exposure.