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This chapter explores the importance of seeds in plant growth, including their role in agriculture, diets, and various purposes. It also discusses seed germination, growth after germination, plant growth hormones, effects of light and gravity, and plant nutrition.
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Chapter 9 Plant Growth
Importance of Seed • Most ag crops begin as seeds • Seeds compose ~70% of diets • Used for varied purposes • Cereals, oils, snacks • Beverages • Oils and dryers • Cosmetics, ointments, pharmas
Types of Seeds • Dicot • Leaf has two distinct halves • Stores energy in cotyledons • Monocot • One seed leaf • Stores energy in endosperm
Seed Germination • Water • Oxygen • Temperature • Light
Process of Germination • Moisture enters seed, seed swells • Coat ruptures, oxygen enters • Respiration provides energy • Cells multiply, growth bidirectional
Growth after Germination • Growth types • Increase in cell size • Increase in cell number • Cell differentiation • Mitosis occurs in meristem • Tips of stems and branches • Tips of roots
Plant Growth Hormones • Chemical substances that control or influence activities • Control growth in plants • Proper balance is essential • Stimulate or inhibit
Major Hormone Groups • Auxins • Cytokinins • Gibberellins
Effects of Light on Plant Growth • Phototropism (grow toward light) • Photoperiodism (respond to amount of daylight and darkness) • Blooming • Leaf shedding • Dormancy • Flowering intervals
Effect of Gravity on Plant Growth • Geotropism (grow toward gravity) • Plant grows in opposite directions • Stem: Negatively geotropic • Root: Positively geotropic
Plant Nutrition • All systems need nutrients • Nutrients provide energy • Come from air and soil • Proper balance is necessary • Macronutrients: In large amounts • Micronutrients: In small amounts
Nonmineral Nutrients • Carbon • Hydrogen • Oxygen
Primary Nutrients • Nitrogen • Phosphorus • Potassium
Secondary Nutrients • Calcium • Magnesium • Sulfur
Micronutrients • Iron • Chlorine • Copper • Zinc • Boron • Manganese • Molybdenum
Summary • Plants grow more efficiently due to human techniques • All use biology principles found in nature • Research uses these principles to grow food and fiber more efficiently