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Plant Nutrition and Transport Notes

Plant Nutrition and Transport

Overview of Plant Nutrients

  • Plants acquire nutrients from air, water, and soil.
  • Sugars produced during photosynthesis utilize:
    • Carbon and oxygen from the atmosphere
    • Hydrogen from water
  • Sugars are utilized to construct organic materials, primarily carbohydrates.

Importance of Water and Nutrient Transport

  • Plants need to transport:
    • Water from roots to leaves.
    • Sugars to various parts of the plant.
  • Cellular respiration breaks down sugars for energy and consumes oxygen.

Mechanisms of Nutrient Uptake

  • Water and Mineral Movement:
    • Water and minerals move upward through the plant's xylem from roots to leaves, facilitated by transpiration.
    • Sugars can flow between shoots (leaves) and roots.
  • Root Hairs increase the absorptive surface of roots:
    • Cells absorb water and solutes via:
    • Transmembrane route: Transporting solutes across cell membranes.
    • Symplastic route: Through the interconnected cytoplasm of cells.
    • Apoplastic route: Through the cell walls and interstitial spaces.

The Role of the Endodermis

  • All absorbed nutrients must pass through the endodermis, which has selective permeability before entering the xylem.

Transpiration and Water Movement

  • Transpiration pulls water up xylem vessels:
    • Water evaporates from stomata, creating tension that draws water up from the roots.
    • This movement is facilitated by cohesion (water molecules stick together) and adhesion (water molecules stick to xylem walls).

Guard Cells and Stomatal Regulation

  • Guard Cells regulate water loss and gas exchange:
    • Generally open during the day for transpiration and closed at night to conserve water.

Phloem Transport: The Distribution of Sugars

  • Phloem transports sugars produced in photosynthesis:
    • Contains sieve-tube elements, which allow flow from source (leaves) to sink (roots or storage areas).
    • Pressure Flow Mechanism:
    • Sugar loading at the source creates high pressure.
    • Water enters from xylem, pushing the phloem sap towards the sink where sugars are unloaded.

Nutrient Definitions and Importance

  • Macronutrients (needed in larger quantities):
    • Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Potassium (K), Calcium (Ca), Magnesium (Mg), Phosphorus (P), Sulfur (S).
  • Micronutrients (needed in trace amounts):
    • Chlorine (Cl), Iron (Fe), Boron (B), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo), Nickel (Ni).

Soil Composition and Plant Health

  • Soil consists of varying sizes of particles (sand, silt, clay).
    • Cation Exchange: Cations are held onto soil particles but can be exchanged with other cations from plant roots, facilitating mineral absorption.
  • Humus is important for water retention, cation exchange, and nutrient supply.

Fertilizers and Nutrient Deficiencies

  • Healthy plants require balanced nutrients:
    • Inorganic and organic fertilizers can amend soil deficiencies.
  • Signs of nutrient deficiencies include stunted growth and discoloration.

Symbiotic Relationships in Nutrient Acquisition

  • Mycorrhizae increase nutrient and water absorption for plants; fungi benefit in return.
  • Nitrogen-fixing Bacteria convert atmospheric nitrogen into forms that are usable by plants.

Nutritional Adaptations of Certain Plants

  • Epiphytes: Grow on other plants, deriving water and nutrients from rain.
  • Parasitic Plants: Absorb sugars and minerals from host plants.
  • Carnivorous Plants: Obtain nitrogen by digesting insects.

Key Terms and Concepts

  • Cation Exchange: The process where certain cations are replaced by others in the soil, aiding in nutrient absorption.
  • Transpiration: The loss of water vapor from plant surfaces, essential for nutrient transport.
  • Phloem Transport Mechanism: The process by which sugars are actively moved from the source to the sink in plants through differences in pressure.

Conclusion

  • The interaction of soil nutrients, plant structures, and transportation mechanisms are crucial for plant health and productivity.