Kundali IQ
Menu ☰
SSC Maths AcademyHomeSchool 6–12Free notesExplore allMy study planSearchExamsTeachers & parentsPricingFAQOpen appGet it on Google Play

Home › Free notes › Class 11 Biology › Plant Growth and Development

Plant Growth and Development – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 13. Notes, key terms, important questions with answers and MCQs.

हिंदी में पढ़ें

Chapter overview

Plant growth is permanent and indeterminate, controlled by plant growth regulators (hormones) and environmental signals like light and temperature.

Growth

  • Phases: meristematic, elongation, maturation; growth curve is sigmoid.
  • Differentiation, dedifferentiation and redifferentiation give plasticity.
  • Growth rates: arithmetic and geometric.

Plant growth regulators

  • Auxins (IAA): apical dominance, rooting, parthenocarpy; gibberellins: stem elongation (bolting), malting.
  • Cytokinins: cell division, delay senescence; ethylene: fruit ripening, abscission; abscisic acid: stress hormone, stomatal closure, dormancy.
  • Photoperiodism (short-day, long-day plants) and vernalisation (cold treatment for flowering).

Key terms

Apical dominance
suppression of lateral buds by the apical bud (auxin)
Vernalisation
low-temperature treatment that promotes flowering
Photoperiodism
response of plants to the relative lengths of day and night, especially for flowering

Important questions with answers

What are the three phases of growth?2 marks

Meristematic (cells divide), elongation (cells enlarge and vacuolate) and maturation (cells differentiate into permanent tissues).

How is a seed's dormancy broken? Give three methods.3 marks

Scarification (scratching or treating the seed coat to let in water and air), chilling or stratification, and treating with gibberellins or changing light and temperature conditions; also removing inhibitors like ABA by leaching.

Describe the discovery and physiological effects of auxins and gibberellins.5 marks

Auxin: Charles and Francis Darwin observed that canary grass coleoptiles bend towards light and that the tip senses light; F.W. Went isolated auxin from oat coleoptile tips using agar blocks. Effects: cell elongation, apical dominance, rooting of stem cuttings, prevention of early fruit and leaf drop, parthenocarpy (tomato), weed control (2,4-D), xylem differentiation. Gibberellins: Kurosawa found that the fungus Gibberella fujikuroi causes "foolish seedling" disease in rice (overgrowth); GA₃ was isolated from it. Effects: stem elongation and bolting in rosette plants, bigger grapes and apples, more sugarcane yield (longer stems), early seed production in conifers, speeding up malting in brewing, and breaking seed dormancy.

Quick revision

  • ABA = stress hormone.
  • Gibberellins cause bolting.
  • Cytokinins delay ageing.

Exam tips

  • Ethylene is the only gaseous plant hormone.
  • Link each hormone to one practical use: auxin – rooting cuttings, weed killer (2,4-D); GA – grape size, sugarcane yield, malting; cytokinin – keeping leaves green; ethylene – ripening fruits; ABA – seed dormancy.

Practice MCQs

  1. The gaseous plant hormone is

    1. auxin
    2. ethylene
    3. gibberellin
    4. cytokinin
    Show answer

    Answer: (b) ethylene. Ripening.

  2. Stress hormone in plants is

    1. IAA
    2. zeatin
    3. GA
    4. ABA
    Show answer

    Answer: (d) ABA. Abscisic acid.

  3. Apical dominance is due to

    1. cytokinins
    2. auxins
    3. ethylene
    4. ABA
    Show answer

    Answer: (b) auxins. IAA from apex.

  4. Bolting in rosette plants is caused by

    1. gibberellin
    2. auxin
    3. ethylene
    4. ABA
    Show answer

    Answer: (a) gibberellin. Gibberellin.

  5. 2,4-D is used as a

    1. fruit ripener
    2. weedicide for dicot weeds
    3. seed germinator
    4. dwarfing agent
    Show answer

    Answer: (b) weedicide for dicot weeds. Synthetic auxin.

  6. Cytokinins mainly

    1. promote cell division and delay senescence
    2. cause leaf fall
    3. ripen fruits
    4. close stomata
    Show answer

    Answer: (a) promote cell division and delay senescence. Cytokinesis.

  7. Low-temperature treatment to induce flowering is

    1. photoperiodism
    2. vernalisation
    3. stratification only
    4. abscission
    Show answer

    Answer: (b) vernalisation. Vernalisation.

  8. The site of perception of photoperiod in plants is the

    1. shoot apex
    2. flowers
    3. roots
    4. leaves
    Show answer

    Answer: (d) leaves. A stimulus then moves to the apex.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.