Plant Growth & Mineral Nutrition
Shared 11/27/2025•82 views
1. Plant Growth Basics Growth: Increase in size & cell number. Plants exhibit open growth (continuous). Occurs at meristems . Phases of Growth Cell Division (Lag Phase): New cells form, slow growth. Cell Enlargement (Log Phase): Cells grow, rapid growth. Cell Maturation (Stationary Phase): Cells specialize, growth slows. The total duration is the Grand Period of Growth . Sigmoid Growth Curve Growth Rate Time Lag Log Stationary Types of Growth Arithmetic Growth: One daughter cell divides, constant rate (e.g., root elongation). Graph: Straight line. $L_t = L_0 + rt$ Geometric Growth: Both daughter cells divide, rapid rate (e.g., embryo development). Graph: S-shaped. $W_1 = W_0 e^{rt}$ Growth Processes Differentiation: Cells specialize. Dedifferentiation: Mature cells become meristematic again. Redifferentiation: Dedifferentiated cells mature again. 2. Plant Hormones (Growth Regulators) Hormone Functions Effect Auxin (IAA) Cell elongation, root growth, apical dominance Promotes Gibberellins (GA) Stem elongation, seed germination, flowering Promotes Cytokinins Cell division, delays aging Promotes Abscisic Acid (ABA) Leaf fall, seed dormancy, stomata closing Inhibits Ethylene Fruit ripening, leaf abscission Ripening 3. Photoperiodism Effect of day length on flowering. Short Day Plants (SDP): Need long night (e.g., Dahlia, Soybean). Flower in winter. Long Day Plants (LDP): Need short night (e.g., Wheat, Spinach). Flower in summer. Day Neutral Plants (DNP): Light period doesn't matter (e.g., Tomato, Sunflower). 4. Vernalization Cold treatment to induce early flowering. Benefits: Faster growth, extended cultivation areas, early harvest. 5. Mineral Nutrition Minerals are absorbed from soil for growth & development, making proteins, chlorophyll, enzymes. Macronutrients (Large Amount) Element Symbol Main Functions Carbon C Organic compounds Hydrogen H Water component Oxygen O Respiration Nitrogen N Proteins, DNA, chlorophyll Phosphorus P DNA, ATP, cell membrane Potassium K Stomata, enzyme activation Calcium Ca Cell wall formation Magnesium Mg Chlorophyll component Sulphur S Proteins Micronutrients (Small Amount) Element Symbol Main Functions Iron Fe Chlorophyll synthesis Manganese Mn Photosynthesis Zinc Zn IAA synthesis Copper Cu Enzyme activation Boron B Pollen germination Chlorine Cl Photosynthesis Deficiency Symptoms Nitrogen: Stunted growth, chlorosis (yellow leaves). Phosphorus: Poor growth, dull green leaves. Potassium: Yellow leaf edges, early death. Iron: Chlorosis (young leaves). 6. Nitrogen Cycle Nitrogen Fixation Converting atmospheric $N_2$ into usable forms ($NH_3$). Biological Fixation: Free-living bacteria: Azotobacter , Cyanobacteria ( Nostoc , Anabaena ). Symbiotic bacteria: Rhizobium (in legume root nodules). Process: $N_2 \rightarrow NH_3$. Requires 16 ATP per $N_2$. Steps in Nitrogen Cycle Nitrogen Fixation: $N_2 \rightarrow NH_3$ (by bacteria). Nitrification: $NH_3 \rightarrow NO_2^-$ ( Nitrosomonas ) $\rightarrow NO_3^-$ ( Nitrobacter ). Plant Absorption: Plants take up $NO_3^-$. Denitrification: $NO_3^- \rightarrow N_2$ (by denitrifying bacteria). Memory Tricks Hormones: AGCAE (Auxin, Gibberellin, Cytokinin, Abscisic acid, Ethylene) Photoperiodism: SLD (Short day-Soybean, Long day-legumes, Day neutral-Daily crops like tomato) Macronutrients: C HOPKNS CaFe Mg (Note: Fe is micronutrient, but included for mnemonic) Growth Phases: DEM (Division, Enlargement, Maturation) Important Points IAA: Indole Acetic Acid (Auxin). ABA: Stress hormone, closes stomata. Ethylene: Artificial fruit ripening. Gibberellins: Can replace vernalization. Critical period: Dark period (for SDP). Necrosis: Death of tissue. 16 ATP: Needed to fix one $N_2$ molecule. Rhizobium: Nitrogen-fixing bacteria in legume roots. Chlorosis: Yellowing of leaves. Denitrification: $NO_3^- \rightarrow N_2$ gas. Quick Revision Table Topic Key Point Growth type Arithmetic vs Geometric Growth curve S-shaped (Sigmoid) Auxin Root growth, cell elongation Gibberellin Stem elongation, breaks dormancy ABA Stress hormone, closes stomata Ethylene Fruit ripening SDP Short day, long night (winter) LDP Long day, short night (summer) Vernalization Cold treatment for flowering Nitrogen fixation $N_2 \rightarrow NH_3$ (by bacteria) Nitrification $NH_3 \rightarrow NO_3^-$ Rhizobium Legume root nodules