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Plant growth and development are fundamental processes regulated by internal and external factors. Understanding these processes is critical for NEET Biology as questions frequently cover plant hormones, tropisms, photoperiodism, vernalization, and stages of growth.
Plant growth refers to irreversible increase in size and mass, whereas development includes maturation, differentiation, and flowering.
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Definition:
Growth is the permanent increase in size and mass of plant organs or cells, usually measured quantitatively.
Types of Growth:
Primary growth → Increase in length (apical meristems: shoot and root tips)
Secondary growth → Increase in girth (lateral meristems: vascular cambium, cork cambium)
NEET Tip:
Apical meristem → elongation; Lateral meristem → thickening
Growth Patterns:
Sigmoid growth curve (S-shaped) is common in plants
Phases: Lag → Log/Exponential → Steady/Plateau
Definition:
Development is the process of growth, differentiation, and maturation leading to functional plant organs.
Stages:
Cell division → Mitotic activity in meristems
Cell elongation → Increase in cell length and volume
Cell differentiation → Formation of specialized tissues
Morphogenesis → Development of shape and form
Organogenesis → Formation of leaves, flowers, roots
Reproduction → Flowering, fruiting, and seed formation
NEET Tip:
Development is regulated by plant hormones and environmental cues
a. Auxins
Promote cell elongation, apical dominance, root initiation
Example: Indole-3-acetic acid (IAA)
NEET Shortcut: “Auxins = Apical dominance & Elongation”
b. Gibberellins (GAs)
Stimulate stem elongation, seed germination, bolting
Example: GA₃ promotes flowering in long-day plants
c. Cytokinins
Promote cell division, delay senescence, stimulate lateral bud growth
Example: Zeatin
d. Abscisic Acid (ABA)
Inhibits growth, induces dormancy, closes stomata under stress
NEET Tip: “ABA = Anti-growth / Stress hormone”
e. Ethylene
Promotes fruit ripening, leaf abscission
Gas hormone
NEET Important Formulas:
Auxin gradient → Tropic responses
GA₃ → Breaks seed dormancy → Germination
Definition:
Directional growth in response to stimuli
Types:
a. Phototropism → Light
Positive → Shoots grow towards light
Negative → Roots grow away
b. Geotropism / Gravitropism → Gravity
Positive → Roots grow downward
Negative → Shoots grow upward
c. Hydrotropism → Water
Roots grow towards moisture
d. Thigmotropism → Touch
Climbing plants, tendrils
NEET Tip:
Auxins redistribute → Causes bending
Definition:
Process by which a dormant seed resumes growth to form a seedling
Steps:
Imbibition → Water absorption, seed swells
Activation of metabolism → Enzyme synthesis, starch → sugar
Radicle emergence → First root
Shoot emergence → Plumule grows upward
NEET Tip:
Gibberellins → Activate α-amylase → Starch hydrolysis → Energy for growth
Photoperiodism:
Response of plants to day length for flowering
Types:
Short-day plants (SDP) → Flower when day < critical length (e.g., Chrysanthemum)
Long-day plants (LDP) → Flower when day > critical length (e.g., Wheat)
Day-neutral plants → Flowering independent of day length
Vernalization:
Promotion of flowering by exposure to cold (winter treatment)
Example: Wheat, Barley
NEET Tip:
Photoperiod + Vernalization → Key in flowering regulation
Senescence: Aging of plant organs
Abscission: Shedding of leaves, flowers, or fruits
Regulated by ethylene (promotes) and auxins (inhibits)
NEET Tip:
Leaf fall in autumn → Ethylene induced abscission
Auxin → Apical dominance, cell elongation, root initiation
GA → Stem elongation, seed germination, flowering
Cytokinin → Cell division, delay senescence
ABA → Dormancy, stomatal closure
Ethylene → Fruit ripening, leaf abscission
Mnemonic for Hormones:
“A Good Cool Apple Ever” → Auxin, Gibberellin, Cytokinin, ABA, Ethylene
Draw diagrams of growth curve, tropism responses, and seed germination
Memorize hormone functions and interactions
Use mnemonics for quick recall of phytohormones
Focus on environmental influences like photoperiodism and vernalization
Plant Growth and Development is a high-yield topic in NEET Biology. Mastery of hormones, tropisms, germination, photoperiodism, and vernalization is essential for scoring in MCQs and diagram-based questions.
With this StudentBro.in guide, students can efficiently revise plant growth formulas, hormonal regulation, and developmental stages, enhancing speed and accuracy during NEET exams.
Remember: Linking stimulus → hormone → response → developmental outcome is the key to mastering Plant Growth and Development for NEET.
