Plant Physiology

Plants require mineral nutrients for growth and life processes.

• Macronutrients: Required in large quantities (e.g., Nitrogen, Magnesium, Potassium, Phosphorus).
  • Nitrogen: Essential for protein, enzyme, and nucleic acid synthesis. Deficiency causes Chlorosis (yellowing).
  • Magnesium: Central component of Chlorophyll; activates enzymes. Deficiency causes yellowing.
• Micronutrients: Required in small quantities (e.g., Iron, Boron, Zinc).

Movement of water, nutrients, and food within the plant.

• Xylem: Transports water and dissolved salts from roots to leaves (Unidirectional).
• Phloem: Transports food (sugar) from leaves to other parts (Bidirectional).

Root Structure: Epidermis with Root Hairs (increase surface area).
Mechanism:

• Root hairs absorb ions by Active Transport (creating high solute concentration).
• Water follows by Osmosis (Passive Transport).
• Path: Epidermis -> Cortex -> Endodermis -> Pericycle -> Xylem.

Loss of water as vapors from aerial parts.

• Stomatal Transpiration: Through Stomata (major type).
• Mechanism of Stomatal Opening:
  • Day: Guard cells uptake $K^+$ ions -> Water enters (Osmosis) -> Turgid -> Stoma Opens.
  • Night: $K^+$ ions leave -> Water leaves -> Flaccid -> Stoma Closes.
• Factors Affecting: Temp (Directly proportional), Wind (Directly), Humidity (Inversely), Surface Area (Directly).

Transpiration Pull: Pulling force created by transpiration that draws water up the xylem (Cohesion-Tension Theory).

Pressure Flow Mechanism:

• Source (Leaves): Sugar loaded into phloem actively -> Water enters by osmosis -> High Pressure.
• Sink (Roots/Fruits): Sugar unloaded -> Water leaves -> Low Pressure.
• Food flows from High Pressure (Source) to Low Pressure (Sink).

• Oxygen: Removed via stomata (daytime).
• Carbon Dioxide: Removed via stomata (nighttime).
• Water: Transpiration and Guttation (loss of liquid water drops from leaf tips at night).
• Metabolic Wastes: Stored in leaves (falling leaves remove waste), or secreted as Latex (Rubber plant), Gums (Keekar), Resins (Conifers), Mucilage (Ladyfinger).

• Hydrophytes (Aquatic): Broad leaves, stomata on upper surface to remove excess water (e.g., Water Lily).
• Xerophytes (Desert): Deep roots, thick cuticle, few stomata, succulent stems to store water (e.g., Cactus).
• Halophytes (Salty): Accumulate salts to keep cells hypertonic, preventing water loss (e.g., Sea grasses).